Bug 1563180 - Prevent synchronization to be ran in parallel multiple times r=glasserc

Differential Revision: https://phabricator.services.mozilla.com/D36921

--HG--
extra : moz-landing-system : lando

services/settings/RemoteSettingsClient.jsm

@@ -193,6 +193,7 @@ class RemoteSettingsClient extends EventEmitter {
     this.localFields = localFields;
     this._lastCheckTimePref = lastCheckTimePref;
     this._verifier = null;
+    this._syncRunning = false;
 
     // This attribute allows signature verification to be disabled, when running tests
     // or when pulling data from a dev server.
@@ -362,6 +363,14 @@ class RemoteSettingsClient extends EventEmitter {
   async maybeSync(expectedTimestamp, options = {}) {
     const { loadDump = true, trigger = "manual" } = options;
 
+    // Make sure we don't run several synchronizations in parallel, mainly
+    // in order to avoid race conditions in "sync" events listeners.
+    if (this._syncRunning) {
+      console.warn(`${this.identifier} sync already running`);
+      return;
+    }
+    this._syncRunning = true;
+
     let importedFromDump = [];
     const startedAt = new Date();
     let reportStatus = null;
@@ -588,6 +597,7 @@ class RemoteSettingsClient extends EventEmitter {
         duration: durationMilliseconds,
       });
       console.debug(`${this.identifier} sync status is ${reportStatus}`);
+      this._syncRunning = false;
     }
   }
 

services/settings/test/unit/test_remote_settings.js

@@ -351,6 +351,20 @@ add_task(async function test_get_does_not_verify_signature_if_load_dump() {
 });
 add_task(clear_state);
 
+add_task(async function test_sync_runs_once_only() {
+  const backup = Utils.log.warn;
+  const messages = [];
+  Utils.log.warn = (m) => {
+    messages.push(m);
+  };
+
+  await Promise.all([client.maybeSync(2000), client.maybeSync(2000)]);
+
+  ok(messages.includes("main/password-fields sync already running"), "warning is shown about sync already running");
+  Utils.log.warn = backup;
+});
+add_task(clear_state);
+
 add_task(
   async function test_sync_pulls_metadata_if_missing_with_dump_is_up_to_date() {
     if (IS_ANDROID) {