Bug 1291821 - Track incomplete stages and re-sync them r=rnewman

Stage re-sync is requested if:
- We hit a 412 either during batching download or batching upload
- We hit a sync deadline either during batching download or when merging records from the buffer

SessionStoreDelegate interface was expanded with onStoreFailed,
indicating that not just a particular record failed, but the whole operation did.

onFetchFailed is used to inform delegates of 412/deadline failures during downloads.
Three new exception types were added, to facilitated messaging between different layers.

MozReview-Commit-ID: Ltdi5noEvdV

--HG--
extra : rebase_source : 9d4af039198b9bc92fbbf25cf8e3d32375a2ab26

mobile/android/base/android-services.mozbuild

@@ -866,6 +866,7 @@ sync_java_files = [TOPSRCDIR + '/mobile/android/services/src/main/java/org/mozil
     'sync/AlreadySyncingException.java',
     'sync/BackoffHandler.java',
     'sync/BadRequiredFieldJSONException.java',
+    'sync/CollectionConcurrentModificationException.java',
     'sync/CollectionKeys.java',
     'sync/CommandProcessor.java',
     'sync/CommandRunner.java',
@@ -944,6 +945,7 @@ sync_java_files = [TOPSRCDIR + '/mobile/android/services/src/main/java/org/mozil
     'sync/NullClusterURLException.java',
     'sync/PersistedMetaGlobal.java',
     'sync/PrefsBackoffHandler.java',
+    'sync/ReflowIsNecessaryException.java',
     'sync/repositories/android/AndroidBrowserBookmarksDataAccessor.java',
     'sync/repositories/android/AndroidBrowserBookmarksRepository.java',
     'sync/repositories/android/AndroidBrowserBookmarksRepositorySession.java',
@@ -1060,6 +1062,7 @@ sync_java_files = [TOPSRCDIR + '/mobile/android/services/src/main/java/org/mozil
     'sync/SyncConfiguration.java',
     'sync/SyncConfigurationException.java',
     'sync/SyncConstants.java',
+    'sync/SyncDeadlineReachedException.java',
     'sync/SyncException.java',
     'sync/synchronizer/ConcurrentRecordConsumer.java',
     'sync/synchronizer/RecordConsumer.java',

mobile/android/services/src/main/java/org/mozilla/gecko/fxa/sync/FxAccountSyncAdapter.java

@@ -53,9 +53,10 @@ import org.mozilla.gecko.tokenserver.TokenServerToken;
 
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.EnumSet;
+import java.util.List;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -123,8 +124,15 @@ public class FxAccountSyncAdapter extends AbstractThreadedSyncAdapter {
       super.rejectSync();
     }
 
+    /* package-local */ void requestFollowUpSync(String stage) {
+      this.stageNamesForFollowUpSync.add(stage);
+    }
+
     protected final Collection<String> stageNamesToSync;
 
+    // Keeps track of incomplete stages during this sync that need to be re-synced once we're done.
+    private final List<String> stageNamesForFollowUpSync = Collections.synchronizedList(new ArrayList<String>());
+
     public SyncDelegate(BlockingQueue<Result> latch, SyncResult syncResult, AndroidFxAccount fxAccount, Collection<String> stageNamesToSync) {
       super(latch, syncResult);
       this.stageNamesToSync = Collections.unmodifiableCollection(stageNamesToSync);
@@ -183,6 +191,15 @@ public class FxAccountSyncAdapter extends AbstractThreadedSyncAdapter {
     public void handleStageCompleted(Stage currentState, GlobalSession globalSession) {
     }
 
+    /**
+     * Schedule an incomplete stage for a follow-up sync.
+     */
+    @Override
+    public void handleIncompleteStage(Stage currentState,
+                                      GlobalSession globalSession) {
+      syncDelegate.requestFollowUpSync(currentState.getRepositoryName());
+    }
+
     @Override
     public void handleSuccess(GlobalSession globalSession) {
       Logger.info(LOG_TAG, "Global session succeeded.");
@@ -574,7 +591,24 @@ public class FxAccountSyncAdapter extends AbstractThreadedSyncAdapter {
       fxAccount.releaseSharedAccountStateLock();
     }
 
-    Logger.info(LOG_TAG, "Syncing done.");
+    // If there are any incomplete stages, request a follow-up sync. Otherwise, we're done.
+    // Incomplete stage is:
+    // - one that hit a 412 error during either upload or download of data, indicating that
+    //   its collection has been modified remotely, or
+    // - one that hit a sync deadline
+    final String[] stagesToSyncAgain;
+    synchronized (syncDelegate.stageNamesForFollowUpSync) {
+      stagesToSyncAgain = syncDelegate.stageNamesForFollowUpSync.toArray(
+              new String[syncDelegate.stageNamesForFollowUpSync.size()]
+      );
+    }
+
+    if (stagesToSyncAgain.length > 0) {
+      Logger.info(LOG_TAG, "Syncing done. Requesting an immediate follow-up sync.");
+      fxAccount.requestImmediateSync(stagesToSyncAgain, null);
+    } else {
+      Logger.info(LOG_TAG, "Syncing done.");
+    }
     lastSyncRealtimeMillis = SystemClock.elapsedRealtime();
   }
 }

mobile/android/services/src/main/java/org/mozilla/gecko/sync/CollectionConcurrentModificationException.java

@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.sync;
+
+/**
+ * Thrown when a collection has been modified by another client while we were either
+ * downloading from it or uploading to it.
+ *
+ * @author grisha
+ */
+public class CollectionConcurrentModificationException extends ReflowIsNecessaryException {
+    private static final long serialVersionUID = 2701457832508838524L;
+}

mobile/android/services/src/main/java/org/mozilla/gecko/sync/GlobalSession.java

@@ -479,6 +479,11 @@ public class GlobalSession implements HttpResponseObserver {
     this.callback.handleError(this, e);
   }
 
+  public void handleIncompleteStage() {
+    // Let our delegate know that current stage is incomplete and needs to be synced again.
+    callback.handleIncompleteStage(this.currentState, this);
+  }
+
   public void handleHTTPError(SyncStorageResponse response, String reason) {
     // TODO: handling of 50x (backoff), 401 (node reassignment or auth error).
     // Fall back to aborting.

mobile/android/services/src/main/java/org/mozilla/gecko/sync/ReflowIsNecessaryException.java

@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.sync;
+
+/**
+ * Used by SynchronizerSession to indicate that reflow of a stage is necessary.
+ * To reflow a stage is to request that it is synced again. Depending on the stage and its current
+ * state (last-synced timestamp, resume context, high-water-mark) we might resume, or sync from a
+ * high-water-mark if allowed, or sync regularly from last-synced timestamp.
+ * A re-sync of a stage is no different from a regular sync of the same stage.
+ *
+ * Stages which complete only partially due to hitting a concurrent collection modification error or
+ * hitting a sync deadline should be re-synced as soon as possible.
+ *
+ * @author grisha
+ */
+public class ReflowIsNecessaryException extends Exception {
+    private static final long serialVersionUID = -2614772437814638768L;
+}

mobile/android/services/src/main/java/org/mozilla/gecko/sync/SyncDeadlineReachedException.java

@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.sync;
+
+/**
+ * Thrown when we've hit a self-imposed sync deadline, and decided not to proceed.
+ *
+ * @author grisha
+ */
+public class SyncDeadlineReachedException extends ReflowIsNecessaryException {
+    private static final long serialVersionUID = 2305367921350245484L;
+}

mobile/android/services/src/main/java/org/mozilla/gecko/sync/delegates/GlobalSessionCallback.java

@@ -38,6 +38,7 @@ public interface GlobalSessionCallback {
   void handleError(GlobalSession globalSession, Exception ex);
   void handleSuccess(GlobalSession globalSession);
   void handleStageCompleted(Stage currentState, GlobalSession globalSession);
+  void handleIncompleteStage(Stage currentState, GlobalSession globalSession);
 
   /**
    * Called when a {@link GlobalSession} wants to know if it should continue

mobile/android/services/src/main/java/org/mozilla/gecko/sync/middleware/BufferingMiddlewareRepositorySession.java

@@ -7,6 +7,7 @@ package org.mozilla.gecko.sync.middleware;
 import android.os.SystemClock;
 import android.support.annotation.VisibleForTesting;
 
+import org.mozilla.gecko.sync.SyncDeadlineReachedException;
 import org.mozilla.gecko.sync.middleware.storage.BufferStorage;
 import org.mozilla.gecko.sync.repositories.InactiveSessionException;
 import org.mozilla.gecko.sync.repositories.NoStoreDelegateException;
@@ -35,8 +36,6 @@ import java.util.concurrent.Executors;
 
     private ExecutorService storeDelegateExecutor = Executors.newSingleThreadExecutor();
 
-    private volatile boolean storeMarkedIncomplete = false;
-
     /* package-local */ BufferingMiddlewareRepositorySession(
             RepositorySession repositorySession, MiddlewareRepository repository,
             long syncDeadlineMillis, BufferStorage bufferStorage) {
@@ -75,9 +74,23 @@ import java.util.concurrent.Executors;
         bufferStorage.addOrReplace(record);
     }
 
+    /**
+     * When source fails to provide all records, we need to decide what to do with the buffer.
+     * We might fail because of a network partition, or because of a concurrent modification of a
+     * collection, or because we ran out of time fetching records, or some other reason.
+     *
+     * Either way we do not clear the buffer in any error scenario, but rather
+     * allow it to be re-filled, replacing existing records with their newer versions if necessary.
+     *
+     * If a collection has been modified, affected records' last-modified timestamps will be bumped,
+     * and we will receive those records during the next sync. If we already have them in our buffer,
+     * we replace our now-old copy. Otherwise, they are new records and we just append them.
+     *
+     * Incoming records are mapped to existing ones via GUIDs.
+     */
     @Override
     public void storeIncomplete() {
-        storeMarkedIncomplete = true;
+        bufferStorage.flush();
     }
 
     @Override
@@ -92,69 +105,43 @@ import java.util.concurrent.Executors;
 
     @Override
     public void storeDone(final long end) {
-        doStoreDonePrepare();
+        bufferStorage.flush();
 
-        // Determine if we have enough time to perform consistency checks on the buffered data and
+        // Determine if we have enough time to merge the buffer data.
-        // then store it. If we don't have enough time now, we keep our buffer and try again later.
+        // If we don't have enough time now, we keep our buffer and try again later.
-        // We don't store results of a buffer consistency check anywhere, so we can't treat it
+        if (!mayProceedToMergeBuffer()) {
-        // separately from storage.
-        if (storeMarkedIncomplete || !mayProceedToMergeBuffer()) {
             super.abort();
-            storeDelegate.deferredStoreDelegate(storeDelegateExecutor).onStoreCompleted(end);
+            storeDelegate.deferredStoreDelegate(storeDelegateExecutor).onStoreFailed(new SyncDeadlineReachedException());
             return;
         }
 
-        // Separate actual merge, so that it may be tested without involving system clock.
+        doMergeBuffer(end);
-        doStoreDone(end);
     }
 
     @VisibleForTesting
-    public void doStoreDonePrepare() {
+    /* package-local */ void doMergeBuffer(long end) {
-        // Now that records stopped flowing, persist them.
+        final Collection<Record> bufferData = bufferStorage.all();
-        bufferStorage.flush();
-    }
-
-    @VisibleForTesting
-    public void doStoreDone(final long end) {
-        final Collection<Record> buffer = bufferStorage.all();
 
         // Trivial case of an empty buffer.
-        if (buffer.isEmpty()) {
+        if (bufferData.isEmpty()) {
             super.storeDone(end);
             return;
         }
 
-        // Flush our buffer to the wrapped local repository. Data goes live!
+        // Let session handle actual storing of records as it pleases.
+        // See Bug 1332094 which is concerned with allowing merge to proceed transactionally.
         try {
-            for (Record record : buffer) {
+            for (Record record : bufferData) {
                 this.inner.store(record);
             }
         } catch (NoStoreDelegateException e) {
-            // At this point we should have a delegate, so this won't happen.
+            // At this point we should have a store delegate set on the session, so this won't happen.
         }
 
-        // And, we're done!
+        // Let session know that there are no more records to store.
         super.storeDone(end);
     }
 
-    /**
-     * When source fails to provide more records, we need to decide what to do with the buffer.
-     * We might fail because of a network partition, or because of a concurrent modification of a
-     * collection. Either way we do not clear the buffer in a general case. If a collection has been
-     * modified, affected records' last-modified timestamps will be bumped, and we will receive those
-     * records during the next sync. If we already have them in our buffer, we replace our now-old
-     * copy. Otherwise, they are new records and we just append them.
-     *
-     * We depend on GUIDs to be a primary key for incoming records.
-     *
-     * @param e indicates reason of failure.
-     */
-    @Override
-    public void sourceFailed(Exception e) {
-        bufferStorage.flush();
-        super.sourceFailed(e);
-    }
-
     /**
      * Session abnormally aborted. This doesn't mean our so-far buffered data is invalid.
      * Clean up after ourselves, if there's anything to clean up.

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/RepositorySession.java

@@ -24,7 +24,7 @@ import org.mozilla.gecko.sync.repositories.domain.Record;
  *
  *<ul>
  * <li>Construct, with a reference to its parent {@link Repository}, by calling
- *   {@link Repository#createSession(RepositorySessionCreationDelegate, android.content.Context)}.</li>
+ *   {@link Repository#createSession(org.mozilla.gecko.sync.repositories.delegates.RepositorySessionCreationDelegate, android.content.Context)}.</li>
  * <li>Populate with saved information by calling {@link #unbundle(RepositorySessionBundle)}.</li>
  * <li>Begin a sync by calling {@link #begin(RepositorySessionBeginDelegate)}. <code>begin()</code>
  *   is an appropriate place to initialize expensive resources.</li>
@@ -158,14 +158,6 @@ public abstract class RepositorySession {
   public void storeFlush() {
   }
 
-  /**
-   * During flow of records, indicates that source failed.
-   *
-   * @param e indicates reason of failure.
-     */
-  public void sourceFailed(Exception e) {
-  }
-
   /**
    * Indicates that a flow of records have been completed.
    */

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/delegates/DeferredRepositorySessionStoreDelegate.java

@@ -54,4 +54,14 @@ public class DeferredRepositorySessionStoreDelegate implements
       }
     });
   }
+
+  @Override
+  public void onStoreFailed(final Exception e) {
+    executor.execute(new Runnable() {
+      @Override
+      public void run() {
+        inner.onStoreFailed(e);
+      }
+    });
+  }
 }

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/delegates/RepositorySessionStoreDelegate.java

@@ -14,10 +14,11 @@ import java.util.concurrent.ExecutorService;
  *
  */
 public interface RepositorySessionStoreDelegate {
-  public void onRecordStoreFailed(Exception ex, String recordGuid);
+  void onRecordStoreFailed(Exception ex, String recordGuid);
 
   // Called with a GUID when store has succeeded.
-  public void onRecordStoreSucceeded(String guid);
+  void onRecordStoreSucceeded(String guid);
-  public void onStoreCompleted(long storeEnd);
+  void onStoreCompleted(long storeEnd);
-  public RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService executor);
+  void onStoreFailed(Exception e);
+  RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService executor);
 }

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/downloaders/BatchingDownloader.java

@@ -10,8 +10,10 @@ import android.support.annotation.Nullable;
 import android.support.annotation.VisibleForTesting;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.CryptoRecord;
 import org.mozilla.gecko.sync.DelayedWorkTracker;
+import org.mozilla.gecko.sync.SyncDeadlineReachedException;
 import org.mozilla.gecko.sync.Utils;
 import org.mozilla.gecko.sync.net.AuthHeaderProvider;
 import org.mozilla.gecko.sync.net.SyncResponse;
@@ -24,7 +26,6 @@ import java.io.UnsupportedEncodingException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.Collections;
-import java.util.ConcurrentModificationException;
 import java.util.HashSet;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -185,9 +186,9 @@ public class BatchingDownloader {
         // We expected server to fail our request with 412 in case of concurrent modifications, so
         // this is unexpected. However, let's treat this case just as if we received a 412.
         if (lastModifiedChanged) {
-            this.abort(
+            this.handleFetchFailed(
                     fetchRecordsDelegate,
-                    new ConcurrentModificationException("Last-modified timestamp has changed unexpectedly")
+                    new CollectionConcurrentModificationException()
             );
             return;
         }
@@ -222,7 +223,7 @@ public class BatchingDownloader {
 
         // Should we proceed, however? Do we have enough time?
         if (!mayProceedWithBatching(fetchDeadline)) {
-            this.abort(fetchRecordsDelegate, new Exception("Not enough time to complete next batch"));
+            this.handleFetchFailed(fetchRecordsDelegate, new SyncDeadlineReachedException());
             return;
         }
 
@@ -242,10 +243,16 @@ public class BatchingDownloader {
         }
     }
 
-    public void onFetchFailed(final Exception ex,
+    private void handleFetchFailed(final RepositorySessionFetchRecordsDelegate fetchRecordsDelegate,
-                              final RepositorySessionFetchRecordsDelegate fetchRecordsDelegate,
+                                  final Exception ex) {
-                              final SyncStorageCollectionRequest request) {
+        handleFetchFailed(fetchRecordsDelegate, ex, null);
-        removeRequestFromPending(request);
+    }
+
+    /* package-local */ void handleFetchFailed(final RepositorySessionFetchRecordsDelegate fetchRecordsDelegate,
+                              final Exception ex,
+                              @Nullable final SyncStorageCollectionRequest request) {
+        this.removeRequestFromPending(request);
+        this.abortRequests();
         this.workTracker.delayWorkItem(new Runnable() {
             @Override
             public void run() {
@@ -291,18 +298,6 @@ public class BatchingDownloader {
         return this.lastModified;
     }
 
-    private void abort(final RepositorySessionFetchRecordsDelegate delegate, final Exception exception) {
-        Logger.error(LOG_TAG, exception.getMessage());
-        this.abortRequests();
-        this.workTracker.delayWorkItem(new Runnable() {
-            @Override
-            public void run() {
-                Logger.debug(LOG_TAG, "Delayed onFetchCompleted running.");
-                delegate.onFetchFailed(exception);
-            }
-        });
-    }
-
     private static boolean mayProceedWithBatching(long deadline) {
         // For simplicity, allow batching to proceed if there's at least a minute left for the sync.
         // This should be enough to fetch and process records in the batch.

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/downloaders/BatchingDownloaderDelegate.java

@@ -5,6 +5,7 @@
 package org.mozilla.gecko.sync.repositories.downloaders;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.CryptoRecord;
 import org.mozilla.gecko.sync.HTTPFailureException;
 import org.mozilla.gecko.sync.crypto.KeyBundle;
@@ -15,8 +16,6 @@ import org.mozilla.gecko.sync.net.WBOCollectionRequestDelegate;
 import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionFetchRecordsDelegate;
 
 
-import java.util.ConcurrentModificationException;
-
 /**
  * Delegate that gets passed into fetch methods to handle server response from fetch.
  */
@@ -60,37 +59,38 @@ public class BatchingDownloaderDelegate extends WBOCollectionRequestDelegate {
     @Override
     public void handleRequestSuccess(SyncStorageResponse response) {
         Logger.debug(LOG_TAG, "Fetch done.");
-        if (response.lastModified() != null) {
+
-            this.downloader.onFetchCompleted(response, this.fetchRecordsDelegate, this.request,
+        // Sanity check.
-                    this.newer, this.batchLimit, this.full, this.sort, this.ids);
+        if (response.lastModified() == null) {
+            this.downloader.handleFetchFailed(
+                    this.fetchRecordsDelegate,
+                    new IllegalStateException("Missing last modified header from response"),
+                    this.request
+            );
             return;
         }
-        this.downloader.onFetchFailed(
+
-                new IllegalStateException("Missing last modified header from response"),
+        this.downloader.onFetchCompleted(response, this.fetchRecordsDelegate, this.request,
-                this.fetchRecordsDelegate,
+                this.newer, this.batchLimit, this.full, this.sort, this.ids);
-                this.request);
     }
 
     @Override
     public void handleRequestFailure(SyncStorageResponse response) {
         Logger.warn(LOG_TAG, "Got a non-success response.");
-        // Handle concurrent modification errors separately. We will need to signal upwards that
+        // Handle concurrent modification errors separately.
-        // this happened, in case stage buffer will want to clean up.
+        final Exception ex;
         if (response.getStatusCode() == 412) {
-            this.downloader.onFetchFailed(
+            ex = new CollectionConcurrentModificationException();
-                    new ConcurrentModificationException(),
-                    this.fetchRecordsDelegate,
-                    this.request
-            );
         } else {
-            this.handleRequestError(new HTTPFailureException(response));
+            ex = new HTTPFailureException(response);
         }
+        this.handleRequestError(ex);
     }
 
     @Override
     public void handleRequestError(final Exception ex) {
         Logger.warn(LOG_TAG, "Got request error.", ex);
-        this.downloader.onFetchFailed(ex, this.fetchRecordsDelegate, this.request);
+        this.downloader.handleFetchFailed(this.fetchRecordsDelegate, ex, this.request);
     }
 
     @Override

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/uploaders/BatchingUploader.java

@@ -8,7 +8,9 @@ import android.net.Uri;
 import android.support.annotation.VisibleForTesting;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.InfoConfiguration;
+import org.mozilla.gecko.sync.Server15PreviousPostFailedException;
 import org.mozilla.gecko.sync.net.AuthHeaderProvider;
 import org.mozilla.gecko.sync.repositories.RepositorySession;
 import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionStoreDelegate;
@@ -16,6 +18,7 @@ import org.mozilla.gecko.sync.repositories.domain.Record;
 
 import java.util.ArrayList;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.atomic.AtomicLong;
 
 /**
@@ -70,6 +73,7 @@ public class BatchingUploader {
     }
 
     // Accessed by the record consumer thread pool.
+    private final ExecutorService executor;
     // Will be re-created, so mark it as volatile.
     private volatile Payload payload;
 
@@ -88,7 +92,7 @@ public class BatchingUploader {
     private final Object payloadLock = new Object();
 
     public BatchingUploader(
-            final RepositorySession repositorySession, final Executor workQueue,
+            final RepositorySession repositorySession, final ExecutorService workQueue,
             final RepositorySessionStoreDelegate sessionStoreDelegate, final Uri baseCollectionUri,
             final Long localCollectionLastModified, final InfoConfiguration infoConfiguration,
             final AuthHeaderProvider authHeaderProvider) {
@@ -102,12 +106,29 @@ public class BatchingUploader {
         this.payload = new Payload(
                 payloadLock, infoConfiguration.maxPostBytes, infoConfiguration.maxPostRecords);
 
-        this.payloadDispatcher = new PayloadDispatcher(workQueue, this, localCollectionLastModified);
+        this.payloadDispatcher = createPayloadDispatcher(workQueue, localCollectionLastModified);
+
+        this.executor = workQueue;
     }
 
     // Called concurrently from the threads running off of a record consumer thread pool.
     public void process(final Record record) {
         final String guid = record.guid;
+
+        // If store failed entirely, just bail out. We've already told our delegate that we failed.
+        if (payloadDispatcher.storeFailed) {
+            return;
+        }
+
+        // If a record or a payload failed, we won't let subsequent requests proceed.'
+        // This means that we may bail much earlier.
+        if (payloadDispatcher.recordUploadFailed) {
+            sessionStoreDelegate.deferredStoreDelegate(executor).onRecordStoreFailed(
+                    new Server15PreviousPostFailedException(), guid
+            );
+            return;
+        }
+
         final byte[] recordBytes = record.toJSONBytes();
         final long recordDeltaByteCount = recordBytes.length + PER_RECORD_OVERHEAD_BYTE_COUNT;
 
@@ -218,7 +239,15 @@ public class BatchingUploader {
         }
     }
 
-    /* package-local */ static class BatchingUploaderException extends Exception {
+    /**
+     * Allows tests to define their own PayloadDispatcher.
+     */
+    @VisibleForTesting
+    PayloadDispatcher createPayloadDispatcher(ExecutorService workQueue, Long localCollectionLastModified) {
+        return new PayloadDispatcher(workQueue, this, localCollectionLastModified);
+    }
+
+    public static class BatchingUploaderException extends Exception {
         private static final long serialVersionUID = 1L;
     }
     /* package-local */ static class LastModifiedDidNotChange extends BatchingUploaderException {

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/uploaders/PayloadDispatcher.java

@@ -8,6 +8,7 @@ import android.support.annotation.Nullable;
 import android.support.annotation.VisibleForTesting;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.Server15RecordPostFailedException;
 import org.mozilla.gecko.sync.net.SyncResponse;
 import org.mozilla.gecko.sync.net.SyncStorageResponse;
@@ -30,12 +31,15 @@ class PayloadDispatcher {
     volatile BatchMeta batchWhiteboard;
     private final AtomicLong uploadTimestamp = new AtomicLong(0);
 
-    // Accessed from different threads sequentially running on the 'executor'.
-    private volatile boolean recordUploadFailed = false;
-
     private final Executor executor;
     private final BatchingUploader uploader;
 
+    // For both of these flags:
+    // Written from sequentially running thread(s) on the SingleThreadExecutor `executor`.
+    // Read by many threads running concurrently on the records consumer thread pool.
+    volatile boolean recordUploadFailed = false;
+    volatile boolean storeFailed = false;
+
     PayloadDispatcher(Executor executor, BatchingUploader uploader, @Nullable Long initialLastModified) {
         // Initially we don't know if we're in a batching mode.
         this.batchWhiteboard = new BatchMeta(initialLastModified, null);
@@ -53,21 +57,7 @@ class PayloadDispatcher {
         executor.execute(new BatchContextRunnable(isCommit) {
             @Override
             public void run() {
-                new RecordUploadRunnable(
+                createRecordUploadRunnable(outgoing, outgoingGuids, byteCount, isCommit, isLastPayload).run();
-                        new BatchingAtomicUploaderMayUploadProvider(),
-                        uploader.collectionUri,
-                        batchWhiteboard.getToken(),
-                        new PayloadUploadDelegate(
-                                uploader.getRepositorySession().getServerRepository().getAuthHeaderProvider(),
-                                PayloadDispatcher.this,
-                                outgoingGuids,
-                                isCommit,
-                                isLastPayload
-                        ),
-                        outgoing,
-                        byteCount,
-                        isCommit
-                ).run();
             }
         });
     }
@@ -142,6 +132,12 @@ class PayloadDispatcher {
         uploader.sessionStoreDelegate.onRecordStoreFailed(e, recordGuid);
     }
 
+    void concurrentModificationDetected() {
+        recordUploadFailed = true;
+        storeFailed = true;
+        uploader.sessionStoreDelegate.onStoreFailed(new CollectionConcurrentModificationException());
+    }
+
     void prepareForNextBatch() {
         batchWhiteboard = batchWhiteboard.nextBatchMeta();
     }
@@ -158,6 +154,31 @@ class PayloadDispatcher {
         }
     }
 
+    /**
+     * Allows tests to define their own RecordUploadRunnable.
+     */
+    @VisibleForTesting
+    Runnable createRecordUploadRunnable(final ArrayList<byte[]> outgoing,
+                                                  final ArrayList<String> outgoingGuids,
+                                                  final long byteCount,
+                                                  final boolean isCommit, final boolean isLastPayload) {
+        return new RecordUploadRunnable(
+                new BatchingAtomicUploaderMayUploadProvider(),
+                uploader.collectionUri,
+                batchWhiteboard.getToken(),
+                new PayloadUploadDelegate(
+                        uploader.authHeaderProvider,
+                        PayloadDispatcher.this,
+                        outgoingGuids,
+                        isCommit,
+                        isLastPayload
+                ),
+                outgoing,
+                byteCount,
+                isCommit
+        );
+    }
+
     /**
      * Allows tests to easily peek into the flow of upload tasks.
      */
@@ -176,6 +197,7 @@ class PayloadDispatcher {
     @VisibleForTesting
     abstract static class NonPayloadContextRunnable implements Runnable {}
 
+    // Instances of this class must be accessed from threads running on the `executor`.
     private class BatchingAtomicUploaderMayUploadProvider implements MayUploadProvider {
         public boolean mayUpload() {
             return !recordUploadFailed;

mobile/android/services/src/main/java/org/mozilla/gecko/sync/repositories/uploaders/PayloadUploadDelegate.java

@@ -184,7 +184,11 @@ class PayloadUploadDelegate implements SyncStorageRequestDelegate {
 
     @Override
     public void handleRequestFailure(final SyncStorageResponse response) {
-        this.handleRequestError(new HTTPFailureException(response));
+        if (response.getStatusCode() == 412) {
+            dispatcher.concurrentModificationDetected();
+        } else {
+            this.handleRequestError(new HTTPFailureException(response));
+        }
     }
 
     @Override

mobile/android/services/src/main/java/org/mozilla/gecko/sync/stage/ServerSyncStage.java

@@ -14,6 +14,7 @@ import org.mozilla.gecko.sync.HTTPFailureException;
 import org.mozilla.gecko.sync.MetaGlobalException;
 import org.mozilla.gecko.sync.NoCollectionKeysSetException;
 import org.mozilla.gecko.sync.NonObjectJSONException;
+import org.mozilla.gecko.sync.ReflowIsNecessaryException;
 import org.mozilla.gecko.sync.SynchronizerConfiguration;
 import org.mozilla.gecko.sync.Utils;
 import org.mozilla.gecko.sync.crypto.KeyBundle;
@@ -622,6 +623,12 @@ public abstract class ServerSyncStage extends AbstractSessionManagingSyncStage i
       }
     }
 
+    // Let global session know that this stage is not complete (due to a 412 or hitting a deadline).
+    // This stage will be re-synced once current sync is complete.
+    if (lastException instanceof ReflowIsNecessaryException) {
+      session.handleIncompleteStage();
+    }
+
     Logger.info(LOG_TAG, "Advancing session even though stage failed (took " + getStageDurationString() +
         "). Timestamps not persisted.");
     session.advance();

mobile/android/services/src/main/java/org/mozilla/gecko/sync/synchronizer/ConcurrentRecordConsumer.java

@@ -65,7 +65,11 @@ class ConcurrentRecordConsumer extends RecordConsumer {
 
   private void consumerIsDone() {
     Logger.debug(LOG_TAG, "Consumer is done. Processed " + counter + ((counter == 1) ? " record." : " records."));
-    delegate.consumerIsDone(allRecordsQueued);
+    if (allRecordsQueued) {
+      delegate.consumerIsDoneFull();
+    } else {
+      delegate.consumerIsDonePartial();
+    }
   }
 
   @Override

mobile/android/services/src/main/java/org/mozilla/gecko/sync/synchronizer/RecordsChannel.java

@@ -4,11 +4,15 @@
 
 package org.mozilla.gecko.sync.synchronizer;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.ReflowIsNecessaryException;
 import org.mozilla.gecko.sync.ThreadPool;
 import org.mozilla.gecko.sync.repositories.InvalidSessionTransitionException;
 import org.mozilla.gecko.sync.repositories.NoStoreDelegateException;
@@ -72,6 +76,8 @@ public class RecordsChannel implements
   private final RecordsChannelDelegate delegate;
   private long fetchEnd = -1;
 
+  private volatile ReflowIsNecessaryException reflowException;
+
   protected final AtomicInteger numFetched = new AtomicInteger();
   protected final AtomicInteger numFetchFailed = new AtomicInteger();
   protected final AtomicInteger numStored = new AtomicInteger();
@@ -93,7 +99,7 @@ public class RecordsChannel implements
    * Then we notify our delegate of completion.
    */
   private RecordConsumer consumer;
-  private boolean waitingForQueueDone = false;
+  private volatile boolean waitingForQueueDone = false;
   private final ConcurrentLinkedQueue<Record> toProcess = new ConcurrentLinkedQueue<Record>();
 
   @Override
@@ -204,9 +210,12 @@ public class RecordsChannel implements
 
   @Override
   public void onFetchFailed(Exception ex) {
-    Logger.warn(LOG_TAG, "onFetchFailed. Informing sink, calling for immediate stop.", ex);
+    Logger.warn(LOG_TAG, "onFetchFailed. Calling for immediate stop.", ex);
-    sink.sourceFailed(ex);
     numFetchFailed.incrementAndGet();
+    if (ex instanceof ReflowIsNecessaryException) {
+      setReflowException((ReflowIsNecessaryException) ex);
+    }
+    // Sink will be informed once consumer finishes.
     this.consumer.halt();
     delegate.onFlowFetchFailed(this, ex);
   }
@@ -246,16 +255,27 @@ public class RecordsChannel implements
     this.consumer.stored();
   }
 
-
   @Override
-  public void consumerIsDone(boolean allRecordsQueued) {
+  public void consumerIsDoneFull() {
-    Logger.trace(LOG_TAG, "Consumer is done. Are we waiting for it? " + waitingForQueueDone);
+    Logger.trace(LOG_TAG, "Consumer is done, processed all records. Are we waiting for it? " + waitingForQueueDone);
     if (waitingForQueueDone) {
       waitingForQueueDone = false;
-      if (!allRecordsQueued) {
+
-        this.sink.storeIncomplete();
+      // Now we'll be waiting for sink to call its delegate's onStoreCompleted or onStoreFailed.
-      }
+      this.sink.storeDone();
-      this.sink.storeDone(); // Now we'll be waiting for onStoreCompleted.
+    }
+  }
+
+  @Override
+  public void consumerIsDonePartial() {
+    Logger.trace(LOG_TAG, "Consumer is done, processed some records. Are we waiting for it? " + waitingForQueueDone);
+    if (waitingForQueueDone) {
+      waitingForQueueDone = false;
+
+      // Let sink clean up or flush records if necessary.
+      this.sink.storeIncomplete();
+
+      delegate.onFlowCompleted(this, fetchEnd, System.currentTimeMillis());
     }
   }
 
@@ -265,9 +285,40 @@ public class RecordsChannel implements
                           "Fetch end is " + fetchEnd + ", store end is " + storeEnd);
     // Source might have used caches used to facilitate flow of records, so now is a good
     // time to clean up. Particularly pertinent for buffered sources.
+    // Rephrasing this in a more concrete way, buffers are cleared only once records have been merged
+    // locally and results of the merge have been uploaded to the server successfully.
     this.source.performCleanup();
-    // TODO: synchronize on consumer callback?
     delegate.onFlowCompleted(this, fetchEnd, storeEnd);
+
+  }
+
+  @Override
+  public void onStoreFailed(Exception ex) {
+    Logger.warn(LOG_TAG, "onStoreFailed. Calling for immediate stop.", ex);
+    if (ex instanceof ReflowIsNecessaryException) {
+      setReflowException((ReflowIsNecessaryException) ex);
+    }
+
+    // NB: consumer might or might not be running at this point. There are two cases here:
+    // 1) If we're storing records remotely, we might fail due to a 412.
+    // -- we might hit 412 at any point, so consumer might be in either state.
+    // Action: ignore consumer state, we have nothing else to do other to inform our delegate
+    // that we're done with this flow. Based on the reflow exception, it'll determine what to do.
+
+    // 2) If we're storing (merging) records locally, we might fail due to a sync deadline.
+    // -- we might hit a deadline only prior to attempting to merge records,
+    // -- at which point consumer would have finished already, and storeDone was called.
+    // Action: consumer state is known (done), so we can ignore it safely and inform our delegate
+    // that we're done.
+
+    // Prevent "once consumer is done..." actions from taking place. They already have (case 2), or
+    // we don't need them (case 1).
+    waitingForQueueDone = false;
+
+    // If consumer is still going at it, tell it to stop.
+    this.consumer.halt();
+
+    delegate.onFlowCompleted(this, fetchEnd, System.currentTimeMillis());
   }
 
   @Override
@@ -310,4 +361,17 @@ public class RecordsChannel implements
     // Lie outright. We know that all of our fetch methods are safe.
     return this;
   }
+
+  @Nullable
+  /* package-local */ synchronized ReflowIsNecessaryException getReflowException() {
+    return reflowException;
+  }
+
+  private synchronized void setReflowException(@NonNull ReflowIsNecessaryException e) {
+    // It is a mistake to set reflow exception multiple times.
+    if (reflowException != null) {
+      throw new IllegalStateException("Reflow exception already set: " + reflowException);
+    }
+    reflowException = e;
+  }
 }

mobile/android/services/src/main/java/org/mozilla/gecko/sync/synchronizer/RecordsConsumerDelegate.java

@@ -9,15 +9,19 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 import org.mozilla.gecko.sync.repositories.domain.Record;
 
 interface RecordsConsumerDelegate {
-  public abstract ConcurrentLinkedQueue<Record> getQueue();
+  ConcurrentLinkedQueue<Record> getQueue();
 
   /**
    * Called when no more items will be processed.
-   * If forced is true, the consumer is terminating because it was told to halt;
+   * Indicates that all items have been processed.
-   * not all items will necessarily have been processed.
-   * If forced is false, the consumer has invoked store and received an onStoreCompleted callback.
-   * @param forced
    */
-  public abstract void consumerIsDone(boolean forced);
+  void consumerIsDoneFull();
-  public abstract void store(Record record);
+
+  /**
+   * Called when no more items will be processed.
+   * Indicates that only some of the items have been processed.
+   */
+  void consumerIsDonePartial();
+
+  void store(Record record);
 }

mobile/android/services/src/main/java/org/mozilla/gecko/sync/synchronizer/ServerLocalSynchronizerSession.java

@@ -5,6 +5,7 @@
 package org.mozilla.gecko.sync.synchronizer;
 
 import org.mozilla.gecko.background.common.log.Logger;
+import org.mozilla.gecko.sync.ReflowIsNecessaryException;
 import org.mozilla.gecko.sync.repositories.FetchFailedException;
 import org.mozilla.gecko.sync.repositories.StoreFailedException;
 
@@ -29,6 +30,15 @@ public class ServerLocalSynchronizerSession extends SynchronizerSession {
 
   @Override
   public void onFirstFlowCompleted(RecordsChannel recordsChannel, long fetchEnd, long storeEnd) {
+    // If a "reflow exception" was thrown, consider this synchronization failed.
+    final ReflowIsNecessaryException reflowException = recordsChannel.getReflowException();
+    if (reflowException != null) {
+      final String message = "Reflow is necessary: " + reflowException;
+      Logger.warn(LOG_TAG, message + " Aborting session.");
+      delegate.onSynchronizeFailed(this, reflowException, message);
+      return;
+    }
+
     // Fetch failures always abort.
     int numRemoteFetchFailed = recordsChannel.getFetchFailureCount();
     if (numRemoteFetchFailed > 0) {
@@ -53,6 +63,15 @@ public class ServerLocalSynchronizerSession extends SynchronizerSession {
 
   @Override
   public void onSecondFlowCompleted(RecordsChannel recordsChannel, long fetchEnd, long storeEnd) {
+    // If a "reflow exception" was thrown, consider this synchronization failed.
+    final ReflowIsNecessaryException reflowException = recordsChannel.getReflowException();
+    if (reflowException != null) {
+      final String message = "Reflow is necessary: " + reflowException;
+      Logger.warn(LOG_TAG, message + " Aborting session.");
+      delegate.onSynchronizeFailed(this, reflowException, message);
+      return;
+    }
+
     // Fetch failures always abort.
     int numLocalFetchFailed = recordsChannel.getFetchFailureCount();
     if (numLocalFetchFailed > 0) {

mobile/android/tests/background/junit3/src/org/mozilla/gecko/background/db/TestBookmarks.java

@@ -746,6 +746,11 @@ public class TestBookmarks extends AndroidSyncTestCase {
           @Override
           public void onRecordStoreSucceeded(String guid) {
           }
+
+          @Override
+          public void onStoreFailed(Exception e) {
+
+          }
         };
         session.setStoreDelegate(storeDelegate);
         for (BookmarkRecord record : records) {

mobile/android/tests/background/junit3/src/org/mozilla/gecko/background/sync/TestStoreTracking.java

@@ -121,6 +121,11 @@ public class TestStoreTracking extends AndroidSyncTestCase {
           performNotify(e);
         }
       }
+
+      @Override
+      public void onStoreFailed(Exception e) {
+
+      }
     };
 
     session.setStoreDelegate(storeDelegate);

mobile/android/tests/background/junit3/src/org/mozilla/gecko/background/sync/helpers/DefaultStoreDelegate.java

@@ -11,7 +11,7 @@ public class DefaultStoreDelegate extends DefaultDelegate implements RepositoryS
 
   @Override
   public void onRecordStoreFailed(Exception ex, String guid) {
-    performNotify("Store failed", ex);
+    performNotify("Record store failed", ex);
   }
 
   @Override
@@ -24,6 +24,11 @@ public class DefaultStoreDelegate extends DefaultDelegate implements RepositoryS
     performNotify("DefaultStoreDelegate used", null);
   }
 
+  @Override
+  public void onStoreFailed(Exception ex) {
+    performNotify("Store failed", ex);
+  }
+
   @Override
   public RepositorySessionStoreDelegate deferredStoreDelegate(final ExecutorService executor) {
     final RepositorySessionStoreDelegate self = this;
@@ -59,6 +64,11 @@ public class DefaultStoreDelegate extends DefaultDelegate implements RepositoryS
         });
       }
 
+      @Override
+      public void onStoreFailed(Exception e) {
+
+      }
+
       @Override
       public RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService newExecutor) {
         if (newExecutor == executor) {

mobile/android/tests/background/junit3/src/org/mozilla/gecko/background/testhelpers/DefaultGlobalSessionCallback.java

@@ -28,6 +28,12 @@ public class DefaultGlobalSessionCallback implements GlobalSessionCallback {
   public void informMigrated(GlobalSession globalSession) {
   }
 
+  @Override
+  public void handleIncompleteStage(Stage currentState,
+                                    GlobalSession globalSession) {
+
+  }
+
   @Override
   public void handleAborted(GlobalSession globalSession, String reason) {
   }

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/SynchronizerHelpers.java

@@ -6,6 +6,8 @@ package org.mozilla.android.sync.test;
 import android.content.Context;
 import org.mozilla.gecko.background.common.log.Logger;
 import org.mozilla.gecko.background.testhelpers.WBORepository;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
+import org.mozilla.gecko.sync.SyncDeadlineReachedException;
 import org.mozilla.gecko.sync.repositories.FetchFailedException;
 import org.mozilla.gecko.sync.repositories.InactiveSessionException;
 import org.mozilla.gecko.sync.repositories.InvalidSessionTransitionException;
@@ -23,10 +25,38 @@ import java.util.concurrent.ExecutorService;
 public class SynchronizerHelpers {
   public static final String FAIL_SENTINEL = "Fail";
 
+  enum FailMode {
+    COLLECTION_MODIFIED,
+    DEADLINE_REACHED,
+    FETCH,
+    STORE
+  }
+
+  private static Exception getFailException(FailMode failMode) {
+    switch (failMode) {
+      case COLLECTION_MODIFIED:
+        return new CollectionConcurrentModificationException();
+      case DEADLINE_REACHED:
+        return new SyncDeadlineReachedException();
+      case FETCH:
+        return new FetchFailedException();
+      case STORE:
+        return new StoreFailedException();
+      default:
+        throw new IllegalStateException();
+    }
+  }
+
   /**
    * Store one at a time, failing if the guid contains FAIL_SENTINEL.
    */
   public static class FailFetchWBORepository extends WBORepository {
+    private final FailMode failMode;
+
+    public FailFetchWBORepository(FailMode failMode) {
+      this.failMode = failMode;
+    }
+
     @Override
     public void createSession(RepositorySessionCreationDelegate delegate,
                               Context context) {
@@ -38,7 +68,7 @@ public class SynchronizerHelpers {
             @Override
             public void onFetchedRecord(Record record) {
               if (record.guid.contains(FAIL_SENTINEL)) {
-                delegate.onFetchFailed(new FetchFailedException());
+                delegate.onFetchFailed(getFailException(failMode));
               } else {
                 delegate.onFetchedRecord(record);
               }
@@ -73,6 +103,12 @@ public class SynchronizerHelpers {
    * Store one at a time, failing if the guid contains FAIL_SENTINEL.
    */
   public static class SerialFailStoreWBORepository extends WBORepository {
+    private final FailMode failMode;
+
+    public SerialFailStoreWBORepository(FailMode failMode) {
+      this.failMode = failMode;
+    }
+
     @Override
     public void createSession(RepositorySessionCreationDelegate delegate,
                               Context context) {
@@ -83,7 +119,12 @@ public class SynchronizerHelpers {
             throw new NoStoreDelegateException();
           }
           if (record.guid.contains(FAIL_SENTINEL)) {
-            storeDelegate.onRecordStoreFailed(new StoreFailedException(), record.guid);
+            Exception ex = getFailException(failMode);
+            if (ex instanceof CollectionConcurrentModificationException) {
+              storeDelegate.onStoreFailed(ex);
+            } else {
+              storeDelegate.onRecordStoreFailed(ex, record.guid);
+            }
           } else {
             super.store(record);
           }

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/TestRecordsChannel.java

@@ -3,6 +3,7 @@
 
 package org.mozilla.android.sync.test;
 
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mozilla.android.sync.test.SynchronizerHelpers.FailFetchWBORepository;
@@ -11,9 +12,10 @@ import org.mozilla.android.sync.test.helpers.ExpectSuccessRepositorySessionFinis
 import org.mozilla.gecko.background.testhelpers.TestRunner;
 import org.mozilla.gecko.background.testhelpers.WBORepository;
 import org.mozilla.gecko.background.testhelpers.WaitHelper;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
+import org.mozilla.gecko.sync.SyncDeadlineReachedException;
 import org.mozilla.gecko.sync.repositories.InactiveSessionException;
 import org.mozilla.gecko.sync.repositories.InvalidSessionTransitionException;
-import org.mozilla.gecko.sync.repositories.Repository;
 import org.mozilla.gecko.sync.repositories.RepositorySession;
 import org.mozilla.gecko.sync.repositories.RepositorySessionBundle;
 import org.mozilla.gecko.sync.repositories.domain.BookmarkRecord;
@@ -30,57 +32,48 @@ import static org.junit.Assert.assertTrue;
 @RunWith(TestRunner.class)
 public class TestRecordsChannel {
 
-  protected WBORepository remote;
+  private WBORepository sourceRepository;
-  protected WBORepository local;
+  private RepositorySession sourceSession;
+  private WBORepository sinkRepository;
+  private RepositorySession sinkSession;
 
-  protected RepositorySession source;
+  private RecordsChannelDelegate rcDelegate;
-  protected RepositorySession sink;
-  protected RecordsChannelDelegate rcDelegate;
 
-  protected AtomicInteger numFlowFetchFailed;
+  private AtomicInteger numFlowFetchFailed;
-  protected AtomicInteger numFlowStoreFailed;
+  private AtomicInteger numFlowStoreFailed;
-  protected AtomicInteger numFlowCompleted;
+  private AtomicInteger numFlowCompleted;
-  protected AtomicBoolean flowBeginFailed;
+  private AtomicBoolean flowBeginFailed;
-  protected AtomicBoolean flowFinishFailed;
+  private AtomicBoolean flowFinishFailed;
 
-  public void doFlow(final Repository remote, final Repository local) throws Exception {
+  private volatile RecordsChannel recordsChannel;
-    WaitHelper.getTestWaiter().performWait(new Runnable() {
+  private volatile Exception fetchException;
-      @Override
+  private volatile Exception storeException;
-      public void run() {
-        remote.createSession(new ExpectSuccessRepositorySessionCreationDelegate(WaitHelper.getTestWaiter()) {
-          @Override
-          public void onSessionCreated(RepositorySession session) {
-            source = session;
-            local.createSession(new ExpectSuccessRepositorySessionCreationDelegate(WaitHelper.getTestWaiter()) {
-              @Override
-              public void onSessionCreated(RepositorySession session) {
-                sink = session;
-                WaitHelper.getTestWaiter().performNotify();
-              }
-            }, null);
-          }
-        }, null);
-      }
-    });
-
-    assertNotNull(source);
-    assertNotNull(sink);
 
+  @Before
+  public void setUp() throws Exception {
     numFlowFetchFailed = new AtomicInteger(0);
     numFlowStoreFailed = new AtomicInteger(0);
     numFlowCompleted = new AtomicInteger(0);
     flowBeginFailed = new AtomicBoolean(false);
     flowFinishFailed = new AtomicBoolean(false);
 
+    // Repositories and sessions will be set/created by tests.
+    sourceRepository = null;
+    sourceSession = null;
+    sinkRepository = null;
+    sinkSession = null;
+
     rcDelegate = new RecordsChannelDelegate() {
       @Override
       public void onFlowFetchFailed(RecordsChannel recordsChannel, Exception ex) {
         numFlowFetchFailed.incrementAndGet();
+        fetchException = ex;
       }
 
       @Override
       public void onFlowStoreFailed(RecordsChannel recordsChannel, Exception ex, String recordGuid) {
         numFlowStoreFailed.incrementAndGet();
+        storeException = ex;
       }
 
       @Override
@@ -93,11 +86,11 @@ public class TestRecordsChannel {
       public void onFlowCompleted(RecordsChannel recordsChannel, long fetchEnd, long storeEnd) {
         numFlowCompleted.incrementAndGet();
         try {
-          sink.finish(new ExpectSuccessRepositorySessionFinishDelegate(WaitHelper.getTestWaiter()) {
+          sinkSession.finish(new ExpectSuccessRepositorySessionFinishDelegate(WaitHelper.getTestWaiter()) {
             @Override
             public void onFinishSucceeded(RepositorySession session, RepositorySessionBundle bundle) {
               try {
-                source.finish(new ExpectSuccessRepositorySessionFinishDelegate(WaitHelper.getTestWaiter()) {
+                sourceSession.finish(new ExpectSuccessRepositorySessionFinishDelegate(WaitHelper.getTestWaiter()) {
                   @Override
                   public void onFinishSucceeded(RepositorySession session, RepositorySessionBundle bundle) {
                     performNotify();
@@ -119,13 +112,39 @@ public class TestRecordsChannel {
         WaitHelper.getTestWaiter().performNotify();
       }
     };
+  }
 
-    final RecordsChannel rc = new RecordsChannel(source,  sink, rcDelegate);
+  private void createSessions() {
+    WaitHelper.getTestWaiter().performWait(new Runnable() {
+      @Override
+      public void run() {
+        sourceRepository.createSession(new ExpectSuccessRepositorySessionCreationDelegate(WaitHelper.getTestWaiter()) {
+          @Override
+          public void onSessionCreated(RepositorySession session) {
+            sourceSession = session;
+            sinkRepository.createSession(new ExpectSuccessRepositorySessionCreationDelegate(WaitHelper.getTestWaiter()) {
+              @Override
+              public void onSessionCreated(RepositorySession session) {
+                sinkSession = session;
+                WaitHelper.getTestWaiter().performNotify();
+              }
+            }, null);
+          }
+        }, null);
+      }
+    });
+  }
+
+  public void doFlow() throws Exception {
+    createSessions();
+    assertNotNull(sourceSession);
+    assertNotNull(sinkSession);
+    recordsChannel = new RecordsChannel(sourceSession,  sinkSession, rcDelegate);
     WaitHelper.getTestWaiter().performWait(new Runnable() {
       @Override
       public void run() {
         try {
-          rc.beginAndFlow();
+          recordsChannel.beginAndFlow();
         } catch (InvalidSessionTransitionException e) {
           WaitHelper.getTestWaiter().performNotify(e);
         }
@@ -133,6 +152,7 @@ public class TestRecordsChannel {
     });
   }
 
+  // NB: records in WBORepository are stored in a HashMap, so don't assume an order.
   public static final BookmarkRecord[] inbounds = new BookmarkRecord[] {
     new BookmarkRecord("inboundSucc1", "bookmarks", 1, false),
     new BookmarkRecord("inboundSucc2", "bookmarks", 1, false),
@@ -145,9 +165,9 @@ public class TestRecordsChannel {
       new BookmarkRecord("outboundSucc1", "bookmarks", 1, false),
       new BookmarkRecord("outboundSucc2", "bookmarks", 1, false),
       new BookmarkRecord("outboundSucc3", "bookmarks", 1, false),
+      new BookmarkRecord("outboundFail6", "bookmarks", 1, false),
       new BookmarkRecord("outboundSucc4", "bookmarks", 1, false),
       new BookmarkRecord("outboundSucc5", "bookmarks", 1, false),
-      new BookmarkRecord("outboundFail6", "bookmarks", 1, false),
   };
 
   protected WBORepository empty() {
@@ -163,8 +183,9 @@ public class TestRecordsChannel {
     return repo;
   }
 
-  protected WBORepository failingFetch() {
+  protected WBORepository failingFetch(SynchronizerHelpers.FailMode failMode) {
-    WBORepository repo = new FailFetchWBORepository();
+    WBORepository repo = new FailFetchWBORepository(failMode);
+
     for (BookmarkRecord outbound : outbounds) {
       repo.wbos.put(outbound.guid, outbound);
     }
@@ -173,57 +194,143 @@ public class TestRecordsChannel {
 
   @Test
   public void testSuccess() throws Exception {
-    WBORepository source = full();
+    sourceRepository = full();
-    WBORepository sink = empty();
+    sinkRepository = empty();
-    doFlow(source, sink);
+    doFlow();
     assertEquals(1, numFlowCompleted.get());
     assertEquals(0, numFlowFetchFailed.get());
     assertEquals(0, numFlowStoreFailed.get());
-    assertEquals(source.wbos, sink.wbos);
+    assertEquals(sourceRepository.wbos, sinkRepository.wbos);
+    assertEquals(0, recordsChannel.getFetchFailureCount());
+    assertEquals(0, recordsChannel.getStoreFailureCount());
+    assertEquals(6, recordsChannel.getStoreCount());
   }
 
   @Test
   public void testFetchFail() throws Exception {
-    WBORepository source = failingFetch();
+    sourceRepository = failingFetch(SynchronizerHelpers.FailMode.FETCH);
-    WBORepository sink = empty();
+    sinkRepository = empty();
-    doFlow(source, sink);
+    doFlow();
     assertEquals(1, numFlowCompleted.get());
     assertTrue(numFlowFetchFailed.get() > 0);
     assertEquals(0, numFlowStoreFailed.get());
-    assertTrue(sink.wbos.size() < 6);
+    assertTrue(sinkRepository.wbos.size() < 6);
+    assertTrue(recordsChannel.getFetchFailureCount() > 0);
+    assertEquals(0, recordsChannel.getStoreFailureCount());
+    assertTrue(recordsChannel.getStoreCount() < 6);
+  }
+
+  @Test
+  public void testStoreFetchFailedCollectionModified() throws Exception {
+    sourceRepository = failingFetch(SynchronizerHelpers.FailMode.COLLECTION_MODIFIED);
+    sinkRepository = empty();
+    doFlow();
+    assertEquals(1, numFlowCompleted.get());
+    assertTrue(numFlowFetchFailed.get() > 0);
+    assertEquals(0, numFlowStoreFailed.get());
+    assertTrue(sinkRepository.wbos.size() < 6);
+
+    assertTrue(recordsChannel.getFetchFailureCount() > 0);
+    assertEquals(0, recordsChannel.getStoreFailureCount());
+    assertTrue(recordsChannel.getStoreCount() < sourceRepository.wbos.size());
+
+    assertEquals(CollectionConcurrentModificationException.class, fetchException.getClass());
+    final Exception ex = recordsChannel.getReflowException();
+    assertNotNull(ex);
+    assertEquals(CollectionConcurrentModificationException.class, ex.getClass());
+  }
+
+  @Test
+  public void testStoreFetchFailedDeadline() throws Exception {
+    sourceRepository = failingFetch(SynchronizerHelpers.FailMode.DEADLINE_REACHED);
+    sinkRepository = empty();
+    doFlow();
+    assertEquals(1, numFlowCompleted.get());
+    assertTrue(numFlowFetchFailed.get() > 0);
+    assertEquals(0, numFlowStoreFailed.get());
+    assertTrue(sinkRepository.wbos.size() < 6);
+
+    assertTrue(recordsChannel.getFetchFailureCount() > 0);
+    assertEquals(0, recordsChannel.getStoreFailureCount());
+    assertTrue(recordsChannel.getStoreCount() < sourceRepository.wbos.size());
+
+    assertEquals(SyncDeadlineReachedException.class, fetchException.getClass());
+    final Exception ex = recordsChannel.getReflowException();
+    assertNotNull(ex);
+    assertEquals(SyncDeadlineReachedException.class, ex.getClass());
   }
 
   @Test
   public void testStoreSerialFail() throws Exception {
-    WBORepository source = full();
+    sourceRepository = full();
-    WBORepository sink = new SynchronizerHelpers.SerialFailStoreWBORepository();
+    sinkRepository = new SynchronizerHelpers.SerialFailStoreWBORepository(
-    doFlow(source, sink);
+            SynchronizerHelpers.FailMode.STORE);
+    doFlow();
     assertEquals(1, numFlowCompleted.get());
     assertEquals(0, numFlowFetchFailed.get());
     assertEquals(1, numFlowStoreFailed.get());
-    assertEquals(5, sink.wbos.size());
+    // We will fail to store one of the records but expect flow to continue.
+    assertEquals(5, sinkRepository.wbos.size());
+
+    assertEquals(0, recordsChannel.getFetchFailureCount());
+    assertEquals(1, recordsChannel.getStoreFailureCount());
+    // Number of store attempts.
+    assertEquals(sourceRepository.wbos.size(), recordsChannel.getStoreCount());
+  }
+
+  @Test
+  public void testStoreSerialFailCollectionModified() throws Exception {
+    sourceRepository = full();
+    sinkRepository = new SynchronizerHelpers.SerialFailStoreWBORepository(
+            SynchronizerHelpers.FailMode.COLLECTION_MODIFIED);
+    doFlow();
+    assertEquals(1, numFlowCompleted.get());
+    assertEquals(0, numFlowFetchFailed.get());
+    assertEquals(1, numFlowStoreFailed.get());
+    // One of the records will fail, at which point we'll stop flowing them.
+    final int sunkenRecords = sinkRepository.wbos.size();
+    assertTrue(sunkenRecords > 0 && sunkenRecords < 6);
+
+    assertEquals(0, recordsChannel.getFetchFailureCount());
+    // RecordChannel's storeFail count is only incremented for failures of individual records.
+    assertEquals(0, recordsChannel.getStoreFailureCount());
+
+    assertEquals(CollectionConcurrentModificationException.class, storeException.getClass());
+    final Exception ex = recordsChannel.getReflowException();
+    assertNotNull(ex);
+    assertEquals(CollectionConcurrentModificationException.class, ex.getClass());
   }
 
   @Test
   public void testStoreBatchesFail() throws Exception {
-    WBORepository source = full();
+    sourceRepository = full();
-    WBORepository sink = new SynchronizerHelpers.BatchFailStoreWBORepository(3);
+    sinkRepository = new SynchronizerHelpers.BatchFailStoreWBORepository(3);
-    doFlow(source, sink);
+    doFlow();
     assertEquals(1, numFlowCompleted.get());
     assertEquals(0, numFlowFetchFailed.get());
     assertEquals(3, numFlowStoreFailed.get()); // One batch fails.
-    assertEquals(3, sink.wbos.size()); // One batch succeeds.
+    assertEquals(3, sinkRepository.wbos.size()); // One batch succeeds.
+
+    assertEquals(0, recordsChannel.getFetchFailureCount());
+    assertEquals(3, recordsChannel.getStoreFailureCount());
+    // Number of store attempts.
+    assertEquals(sourceRepository.wbos.size(), recordsChannel.getStoreCount());
   }
 
 
   @Test
   public void testStoreOneBigBatchFail() throws Exception {
-    WBORepository source = full();
+    sourceRepository = full();
-    WBORepository sink = new SynchronizerHelpers.BatchFailStoreWBORepository(50);
+    sinkRepository = new SynchronizerHelpers.BatchFailStoreWBORepository(50);
-    doFlow(source, sink);
+    doFlow();
     assertEquals(1, numFlowCompleted.get());
     assertEquals(0, numFlowFetchFailed.get());
     assertEquals(6, numFlowStoreFailed.get()); // One (big) batch fails.
-    assertEquals(0, sink.wbos.size()); // No batches succeed.
+    assertEquals(0, sinkRepository.wbos.size()); // No batches succeed.
+
+    assertEquals(0, recordsChannel.getFetchFailureCount());
+    assertEquals(6, recordsChannel.getStoreFailureCount());
+    // Number of store attempts.
+    assertEquals(sourceRepository.wbos.size(), recordsChannel.getStoreCount());
   }
 }

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/TestServer15RepositorySession.java

@@ -12,6 +12,7 @@ import org.mozilla.android.sync.test.helpers.BaseTestStorageRequestDelegate;
 import org.mozilla.android.sync.test.helpers.HTTPServerTestHelper;
 import org.mozilla.android.sync.test.helpers.MockServer;
 import org.mozilla.gecko.background.testhelpers.TestRunner;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.InfoCollections;
 import org.mozilla.gecko.sync.InfoConfiguration;
 import org.mozilla.gecko.sync.Utils;
@@ -22,6 +23,7 @@ import org.mozilla.gecko.sync.net.BaseResource;
 import org.mozilla.gecko.sync.net.BasicAuthHeaderProvider;
 import org.mozilla.gecko.sync.net.SyncStorageResponse;
 import org.mozilla.gecko.sync.repositories.FetchFailedException;
+import org.mozilla.gecko.sync.repositories.NonPersistentRepositoryStateProvider;
 import org.mozilla.gecko.sync.repositories.Server15Repository;
 import org.mozilla.gecko.sync.repositories.StoreFailedException;
 import org.mozilla.gecko.sync.repositories.domain.BookmarkRecord;
@@ -112,7 +114,8 @@ public class TestServer15RepositorySession {
     final TrackingWBORepository local = getLocal(100);
     final Server15Repository remote = new Server15Repository(
             COLLECTION, SystemClock.elapsedRealtime() + TimeUnit.MINUTES.toMillis(30),
-            getCollectionURL(COLLECTION), authHeaderProvider, infoCollections, infoConfiguration);
+            getCollectionURL(COLLECTION), authHeaderProvider, infoCollections, infoConfiguration,
+            new NonPersistentRepositoryStateProvider());
     KeyBundle collectionKey = new KeyBundle(TEST_USERNAME, SYNC_KEY);
     Crypto5MiddlewareRepository cryptoRepo = new Crypto5MiddlewareRepository(remote, collectionKey);
     cryptoRepo.recordFactory = new BookmarkRecordFactory();
@@ -142,6 +145,14 @@ public class TestServer15RepositorySession {
     assertEquals(FetchFailedException.class, e.getClass());
   }
 
+  @Test
+  public void testFetch412Failure() throws Exception {
+    MockServer server = new MockServer(412, "error");
+    Exception e = doSynchronize(server);
+    assertNotNull(e);
+    assertEquals(CollectionConcurrentModificationException.class, e.getClass());
+  }
+
   @Test
   public void testStorePostSuccessWithFailingRecords() throws Exception {
     MockServer server = new MockServer(200, "{ modified: \" + " + Utils.millisecondsToDecimalSeconds(System.currentTimeMillis()) + ", " +

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/TestServerLocalSynchronizer.java

@@ -107,7 +107,7 @@ public class TestServerLocalSynchronizer {
   @Test
   public void testLocalFetchErrors() {
     WBORepository remote = new TrackingWBORepository();
-    WBORepository local  = new FailFetchWBORepository();
+    WBORepository local  = new FailFetchWBORepository(SynchronizerHelpers.FailMode.FETCH);
 
     Synchronizer synchronizer = getSynchronizer(remote, local);
     Exception e = doSynchronize(synchronizer);
@@ -121,7 +121,7 @@ public class TestServerLocalSynchronizer {
 
   @Test
   public void testRemoteFetchErrors() {
-    WBORepository remote = new FailFetchWBORepository();
+    WBORepository remote = new FailFetchWBORepository(SynchronizerHelpers.FailMode.FETCH);
     WBORepository local  = new TrackingWBORepository();
 
     Synchronizer synchronizer = getSynchronizer(remote, local);
@@ -137,7 +137,7 @@ public class TestServerLocalSynchronizer {
   @Test
   public void testLocalSerialStoreErrorsAreIgnored() {
     WBORepository remote = new TrackingWBORepository();
-    WBORepository local  = new SerialFailStoreWBORepository();
+    WBORepository local  = new SerialFailStoreWBORepository(SynchronizerHelpers.FailMode.FETCH);
 
     Synchronizer synchronizer = getSynchronizer(remote, local);
     assertNull(doSynchronize(synchronizer));
@@ -158,7 +158,7 @@ public class TestServerLocalSynchronizer {
 
   @Test
   public void testRemoteSerialStoreErrorsAreNotIgnored() throws Exception {
-    Synchronizer synchronizer = getSynchronizer(new SerialFailStoreWBORepository(), new TrackingWBORepository()); // Tracking so we don't send incoming records back.
+    Synchronizer synchronizer = getSynchronizer(new SerialFailStoreWBORepository(SynchronizerHelpers.FailMode.STORE), new TrackingWBORepository()); // Tracking so we don't send incoming records back.
 
     Exception e = doSynchronize(synchronizer);
     assertNotNull(e);

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/helpers/ExpectSuccessRepositorySessionStoreDelegate.java

@@ -32,6 +32,12 @@ public class ExpectSuccessRepositorySessionStoreDelegate extends
     log("Record store completed at " + storeEnd);
   }
 
+  @Override
+  public void onStoreFailed(Exception e) {
+    log("Store failed.", e);
+    performNotify(new AssertionFailedError("onStoreFailed: store should not have failed."));
+  }
+
   @Override
   public RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService executor) {
     return this;

mobile/android/tests/background/junit4/src/org/mozilla/android/sync/test/helpers/MockGlobalSessionCallback.java

@@ -56,6 +56,12 @@ public class MockGlobalSessionCallback implements GlobalSessionCallback {
     this.testWaiter().performNotify();
   }
 
+  @Override
+  public void handleIncompleteStage(Stage currentState,
+                                    GlobalSession globalSession) {
+
+  }
+
   @Override
   public void handleStageCompleted(Stage currentState,
            GlobalSession globalSession) {

mobile/android/tests/background/junit4/src/org/mozilla/gecko/background/testhelpers/DefaultGlobalSessionCallback.java

@@ -44,6 +44,12 @@ public class DefaultGlobalSessionCallback implements GlobalSessionCallback {
                                    GlobalSession globalSession) {
   }
 
+  @Override
+  public void handleIncompleteStage(Stage currentState,
+                                    GlobalSession globalSession) {
+
+  }
+
   @Override
   public boolean shouldBackOffStorage() {
     return false;

mobile/android/tests/background/junit4/src/org/mozilla/gecko/sync/middleware/BufferingMiddlewareRepositorySessionTest.java

@@ -81,13 +81,8 @@ public class BufferingMiddlewareRepositorySessionTest {
 
     @Test
     public void storeDone() throws Exception {
-        // Verify that storage's flush is called.
-        verify(bufferStorageMocked, times(0)).flush();
-        bufferingSessionMocked.doStoreDonePrepare();
-        verify(bufferStorageMocked, times(1)).flush();
-
         // Trivial case, no records to merge.
-        bufferingSession.doStoreDone(123L);
+        bufferingSession.doMergeBuffer(123L);
         verify(innerRepositorySession, times(1)).storeDone(123L);
         verify(innerRepositorySession, never()).store(any(Record.class));
 
@@ -109,7 +104,7 @@ public class BufferingMiddlewareRepositorySessionTest {
         bufferingSession.store(record4);
 
         // Done storing.
-        bufferingSession.doStoreDone(123L);
+        bufferingSession.doMergeBuffer(123L);
 
         // Ensure all records where stored in the wrapped session.
         verify(innerRepositorySession, times(1)).store(record);
@@ -154,32 +149,6 @@ public class BufferingMiddlewareRepositorySessionTest {
         assertEquals(0, bufferStorage.all().size());
     }
 
-    @Test
-    public void sourceFailed() throws Exception {
-        // Source failes before any records have been stored.
-        bufferingSession.sourceFailed(new Exception());
-        assertEquals(0, bufferStorage.all().size());
-
-        // Store some records now.
-        MockRecord record = new MockRecord("guid1", null, 1, false);
-        bufferingSession.store(record);
-
-        MockRecord record2 = new MockRecord("guid2", null, 13, false);
-        bufferingSession.store(record2);
-
-        MockRecord record3 = new MockRecord("guid3", null, 5, false);
-        bufferingSession.store(record3);
-
-        // Verify that buffer is intact after source fails.
-        bufferingSession.sourceFailed(new Exception());
-        assertEquals(3, bufferStorage.all().size());
-
-        // Verify that buffer is flushed after source fails.
-        verify(bufferStorageMocked, times(0)).flush();
-        bufferingSessionMocked.sourceFailed(new Exception());
-        verify(bufferStorageMocked, times(1)).flush();
-    }
-
     @Test
     public void abort() throws Exception {
         MockRecord record = new MockRecord("guid1", null, 1, false);

mobile/android/tests/background/junit4/src/org/mozilla/gecko/sync/repositories/downloaders/BatchingDownloaderDelegateTest.java

@@ -11,6 +11,7 @@ import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mozilla.gecko.background.testhelpers.TestRunner;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.CryptoRecord;
 import org.mozilla.gecko.sync.HTTPFailureException;
 import org.mozilla.gecko.sync.InfoCollections;
@@ -66,8 +67,8 @@ public class BatchingDownloaderDelegateTest {
         }
 
         @Override
-        public void onFetchFailed(final Exception ex,
+        public void handleFetchFailed(final RepositorySessionFetchRecordsDelegate fetchRecordsDelegate,
-                                  final RepositorySessionFetchRecordsDelegate fetchRecordsDelegate,
+                                  final Exception ex,
                                   final SyncStorageCollectionRequest request) {
             this.isFailure = true;
             this.ex = ex;
@@ -173,6 +174,18 @@ public class BatchingDownloaderDelegateTest {
         assertFalse(mockDownloader.isFetched);
     }
 
+    @Test
+    public void testFailure412() throws Exception {
+        BatchingDownloaderDelegate downloaderDelegate = new BatchingDownloaderDelegate(mockDownloader, null,
+                new SyncStorageCollectionRequest(new URI(DEFAULT_COLLECTION_URL)), 0, 0, true, null, null);
+        SyncStorageResponse response = makeSyncStorageResponse(412, null);
+        downloaderDelegate.handleRequestFailure(response);
+        assertTrue(mockDownloader.isFailure);
+        assertEquals(CollectionConcurrentModificationException.class, mockDownloader.ex.getClass());
+        assertFalse(mockDownloader.isSuccess);
+        assertFalse(mockDownloader.isFetched);
+    }
+
     @Test
     public void testFailureRequestError() throws Exception {
         BatchingDownloaderDelegate downloaderDelegate = new BatchingDownloaderDelegate(mockDownloader, null,

mobile/android/tests/background/junit4/src/org/mozilla/gecko/sync/repositories/downloaders/BatchingDownloaderTest.java

@@ -353,7 +353,7 @@ public class BatchingDownloaderTest {
     public void testFailureException() throws Exception {
         Exception ex = new IllegalStateException();
         SyncStorageCollectionRequest request = new SyncStorageCollectionRequest(new URI("http://dummy.url"));
-        mockDownloader.onFetchFailed(ex, sessionFetchRecordsDelegate, request);
+        mockDownloader.handleFetchFailed(sessionFetchRecordsDelegate, ex, request);
 
         assertFalse(sessionFetchRecordsDelegate.isSuccess);
         assertFalse(sessionFetchRecordsDelegate.isFetched);

mobile/android/tests/background/junit4/src/org/mozilla/gecko/sync/repositories/uploaders/BatchingUploaderTest.java

@@ -18,19 +18,28 @@ import org.mozilla.gecko.sync.ExtendedJSONObject;
 import org.mozilla.gecko.sync.InfoCollections;
 import org.mozilla.gecko.sync.InfoConfiguration;
 import org.mozilla.gecko.sync.Utils;
+import org.mozilla.gecko.sync.net.AuthHeaderProvider;
+import org.mozilla.gecko.sync.repositories.RepositorySession;
 import org.mozilla.gecko.sync.repositories.Server15Repository;
 import org.mozilla.gecko.sync.repositories.Server15RepositorySession;
 import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionStoreDelegate;
 
 import java.net.URISyntaxException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 import java.util.Random;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 
 @RunWith(TestRunner.class)
 public class BatchingUploaderTest {
-    class MockExecutorService implements Executor {
+    class MockExecutorService implements ExecutorService {
         int totalPayloads = 0;
         int commitPayloads = 0;
 
@@ -47,6 +56,71 @@ public class BatchingUploaderTest {
             }
             command.run();
         }
+
+        @Override
+        public void shutdown() {}
+
+        @NonNull
+        @Override
+        public List<Runnable> shutdownNow() {
+            return null;
+        }
+
+        @Override
+        public boolean isShutdown() {
+            return false;
+        }
+
+        @Override
+        public boolean isTerminated() {
+            return false;
+        }
+
+        @Override
+        public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
+            return false;
+        }
+
+        @NonNull
+        @Override
+        public <T> Future<T> submit(Callable<T> task) {
+            return null;
+        }
+
+        @NonNull
+        @Override
+        public <T> Future<T> submit(Runnable task, T result) {
+            return null;
+        }
+
+        @NonNull
+        @Override
+        public Future<?> submit(Runnable task) {
+            return null;
+        }
+
+        @NonNull
+        @Override
+        public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException {
+            return null;
+        }
+
+        @NonNull
+        @Override
+        public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException {
+            return null;
+        }
+
+        @NonNull
+        @Override
+        public <T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, ExecutionException {
+            return null;
+        }
+
+        @Override
+        public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
+            return null;
+        }
     }
 
     class MockStoreDelegate implements RepositorySessionStoreDelegate {
@@ -69,13 +143,18 @@ public class BatchingUploaderTest {
             ++storeCompleted;
         }
 
+        @Override
+        public void onStoreFailed(Exception e) {
+
+        }
+
         @Override
         public RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService executor) {
             return null;
         }
     }
 
-    private Executor workQueue;
+    private ExecutorService workQueue;
     private RepositorySessionStoreDelegate storeDelegate;
 
     @Before
@@ -442,11 +521,41 @@ public class BatchingUploaderTest {
                 makeCountConstrainedRepository(maxPostRecords, maxTotalRecords, firstSync)
         );
         server15RepositorySession.setStoreDelegate(storeDelegate);
-        return new BatchingUploader(
+        return new MockUploader(
-                server15RepositorySession, workQueue, storeDelegate, Uri.EMPTY, null,
+                server15RepositorySession, workQueue, storeDelegate, Uri.EMPTY, 0L,
                 new InfoConfiguration(infoConfigurationJSON), null);
     }
 
+    class MockPayloadDispatcher extends PayloadDispatcher {
+        MockPayloadDispatcher(final Executor workQueue, final BatchingUploader uploader, Long lastModified) {
+            super(workQueue, uploader, lastModified);
+        }
+
+        @Override
+        Runnable createRecordUploadRunnable(ArrayList<byte[]> outgoing, ArrayList<String> outgoingGuids, long byteCount, boolean isCommit, boolean isLastPayload) {
+            // No-op runnable. We don't want this to actually do any work for these tests.
+            return new Runnable() {
+                @Override
+                public void run() {}
+            };
+        }
+    }
+
+    class MockUploader extends BatchingUploader {
+        MockUploader(final RepositorySession repositorySession, final ExecutorService workQueue,
+                     final RepositorySessionStoreDelegate sessionStoreDelegate, final Uri baseCollectionUri,
+                     final Long localCollectionLastModified, final InfoConfiguration infoConfiguration,
+                     final AuthHeaderProvider authHeaderProvider) {
+            super(repositorySession, workQueue, sessionStoreDelegate, baseCollectionUri,
+                    localCollectionLastModified, infoConfiguration, authHeaderProvider);
+        }
+
+        @Override
+        PayloadDispatcher createPayloadDispatcher(ExecutorService workQueue, Long localCollectionLastModified) {
+            return new MockPayloadDispatcher(workQueue, this, localCollectionLastModified);
+        }
+    }
+
     private Server15Repository makeCountConstrainedRepository(long maxPostRecords, long maxTotalRecords, boolean firstSync) {
         return makeConstrainedRepository(1024, 1024, maxPostRecords, 4096, maxTotalRecords, firstSync);
     }

mobile/android/tests/background/junit4/src/org/mozilla/gecko/sync/repositories/uploaders/PayloadUploadDelegateTest.java

@@ -3,15 +3,22 @@
 
 package org.mozilla.gecko.sync.repositories.uploaders;
 
+import android.net.Uri;
+
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mozilla.gecko.background.testhelpers.TestRunner;
+import org.mozilla.gecko.sync.CollectionConcurrentModificationException;
 import org.mozilla.gecko.sync.HTTPFailureException;
+import org.mozilla.gecko.sync.InfoConfiguration;
 import org.mozilla.gecko.sync.NonObjectJSONException;
 import org.mozilla.gecko.sync.net.AuthHeaderProvider;
 import org.mozilla.gecko.sync.net.SyncResponse;
 import org.mozilla.gecko.sync.net.SyncStorageResponse;
+import org.mozilla.gecko.sync.repositories.RepositorySession;
+import org.mozilla.gecko.sync.repositories.RepositoryStateProvider;
+import org.mozilla.gecko.sync.repositories.delegates.RepositorySessionStoreDelegate;
 
 import static org.mockito.Mockito.mock;
 
@@ -19,6 +26,7 @@ import java.io.ByteArrayInputStream;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 
 import ch.boye.httpclientandroidlib.HttpResponse;
 import ch.boye.httpclientandroidlib.ProtocolVersion;
@@ -33,6 +41,8 @@ public class PayloadUploadDelegateTest {
     private PayloadDispatcher payloadDispatcher;
     private AuthHeaderProvider authHeaderProvider;
 
+    private RepositorySessionStoreDelegate sessionStoreDelegate;
+
     class MockPayloadDispatcher extends PayloadDispatcher {
         public final HashMap<String, Exception> failedRecords = new HashMap<>();
         public boolean didLastPayloadFail = false;
@@ -66,6 +76,7 @@ public class PayloadUploadDelegateTest {
 
         @Override
         public void recordFailed(final Exception e, final String recordGuid) {
+            recordUploadFailed = true;
             failedRecords.put(recordGuid, e);
         }
 
@@ -75,11 +86,44 @@ public class PayloadUploadDelegateTest {
         }
     }
 
+    class MockRepositorySessionStoreDelegate implements RepositorySessionStoreDelegate {
+        Exception storeFailedException;
+        ArrayList<String> succeededGuids = new ArrayList<>();
+        HashMap<String, Exception> failedGuids = new HashMap<>();
+
+        @Override
+        public void onRecordStoreFailed(Exception ex, String recordGuid) {
+            failedGuids.put(recordGuid, ex);
+        }
+
+        @Override
+        public void onRecordStoreSucceeded(String guid) {
+            succeededGuids.add(guid);
+        }
+
+        @Override
+        public void onStoreCompleted(long storeEnd) {
+
+        }
+
+        @Override
+        public void onStoreFailed(Exception e) {
+            storeFailedException = e;
+        }
+
+        @Override
+        public RepositorySessionStoreDelegate deferredStoreDelegate(ExecutorService executor) {
+            return null;
+        }
+    }
+
     @Before
     public void setUp() throws Exception {
+        sessionStoreDelegate = new MockRepositorySessionStoreDelegate();
+
         payloadDispatcher = new MockPayloadDispatcher(
                 null,
-                mock(BatchingUploader.class)
+                new BatchingUploader(mock(RepositorySession.class), null, sessionStoreDelegate, Uri.parse("https://example.com"), 0L, mock(InfoConfiguration.class), mock(AuthHeaderProvider.class))
         );
 
         authHeaderProvider = mock(AuthHeaderProvider.class);
@@ -368,6 +412,26 @@ public class PayloadUploadDelegateTest {
         payloadUploadDelegate.handleRequestFailure(new SyncStorageResponse(response));
         assertEquals(3, ((MockPayloadDispatcher) payloadDispatcher).failedRecords.size());
         assertTrue(((MockPayloadDispatcher) payloadDispatcher).didLastPayloadFail);
+        assertTrue(payloadDispatcher.recordUploadFailed);
+    }
+
+    @Test
+    public void testHandleRequestFailure412() {
+        ArrayList<String> postedGuids = new ArrayList<>(3);
+        postedGuids.add("testGuid1");
+        postedGuids.add("testGuid2");
+        postedGuids.add("testGuid3");
+        PayloadUploadDelegate payloadUploadDelegate = new PayloadUploadDelegate(authHeaderProvider, payloadDispatcher, postedGuids, false, false);
+
+        final HttpResponse response = new BasicHttpResponse(
+                new BasicStatusLine(new ProtocolVersion("HTTP", 1, 1), 412, "Precondition failed"));
+        payloadUploadDelegate.handleRequestFailure(new SyncStorageResponse(response));
+
+        assertEquals(0, ((MockPayloadDispatcher) payloadDispatcher).failedRecords.size());
+        assertTrue(payloadDispatcher.recordUploadFailed);
+        assertTrue(payloadDispatcher.storeFailed);
+
+        assertTrue(((MockRepositorySessionStoreDelegate) sessionStoreDelegate).storeFailedException instanceof CollectionConcurrentModificationException);
     }
 
     @Test