Bug 1612283 - Enforce max staleness of 60s in GV Streaming Telemetry r=janerik

Differential Revision: https://phabricator.services.mozilla.com/D61838

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

modules/libpref/init/StaticPrefList.yaml

@@ -7958,6 +7958,11 @@
   value: 5000
   mirror: always
 
+- name: toolkit.telemetry.geckoview.maxBatchStalenessMS
+  type: RelaxedAtomicUint32
+  value: 60000
+  mirror: always
+
 - name: toolkit.telemetry.geckoview.streaming
   type: RelaxedAtomicBool
   value: false

toolkit/components/telemetry/docs/internals/preferences.rst

@@ -246,9 +246,16 @@ GeckoView
 
 ``toolkit.telemetry.geckoview.batchDurationMS``
 
-   The duration in milliseconds over which `GeckoView Streaming Telemetry <../internals/geckoview-streaming>` will batch accumulations before passing it on to its delegate.
+   The duration in milliseconds over which :doc:`GeckoView Streaming Telemetry <../internals/geckoview-streaming>` will batch accumulations before passing it on to its delegate.
    Defaults to 5000.
 
+``toolkit.telemetry.geckoview.maxBatchStalenessMS``
+
+   The maximum time (in milliseconds) between flushes of the
+   :doc:`GeckoView Streaming Telemetry <../internals/geckoview-streaming>`
+   batch to its delegate.
+   Defaults to 60000.
+
 Testing
 -------
 

toolkit/components/telemetry/geckoview/streaming/GeckoViewStreamingTelemetry.cpp

@@ -10,9 +10,11 @@
 #include "mozilla/Services.h"
 #include "mozilla/StaticMutex.h"
 #include "mozilla/StaticPrefs_toolkit.h"
+#include "mozilla/SystemGroup.h"
 #include "mozilla/TimeStamp.h"
 #include "nsDataHashtable.h"
 #include "nsIObserverService.h"
+#include "nsITimer.h"
 #include "nsTArray.h"
 #include "nsThreadUtils.h"
 
@@ -20,6 +22,8 @@ using mozilla::Runnable;
 using mozilla::StaticMutexAutoLock;
 using mozilla::StaticMutexNotRecorded;
 using mozilla::StaticRefPtr;
+using mozilla::SystemGroup;
+using mozilla::TaskCategory;
 using mozilla::TimeStamp;
 
 // Batches and streams Telemetry samples to a JNI delegate which will
@@ -58,6 +62,10 @@ StaticRefPtr<LifecycleObserver> gObserver;
 
 // -- End of gMutex-protected thread-unsafe-accessed data
 
+// Timer that ensures data in the batch never gets too stale.
+// This timer may only be manipulated on the Main Thread.
+StaticRefPtr<nsITimer> gJICTimer;
+
 class LifecycleObserver final : public nsIObserver {
  public:
   NS_DECL_ISUPPORTS
@@ -106,6 +114,10 @@ class SendBatchRunnable : public Runnable {
     MOZ_ASSERT(NS_IsMainThread());
     MOZ_ASSERT(mDelegate);
 
+    if (gJICTimer) {
+      gJICTimer->Cancel();
+    }
+
     for (auto iter = mBatch.Iter(); !iter.Done(); iter.Next()) {
       const nsCString& histogramName = PromiseFlatCString(iter.Key());
       const nsTArray<uint32_t>& samples = iter.Data();
@@ -195,7 +207,29 @@ void BatchCheck(const StaticMutexAutoLock& aLock) {
     }
   }
   if (gBatchBegan.IsNull()) {
+    // Time to begin a new batch.
     gBatchBegan = TimeStamp::Now();
+    // Set a just-in-case timer to enforce an upper-bound on batch staleness.
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        "GeckoviewStreamingTelemetry::ArmTimer", []() -> void {
+          if (!gJICTimer) {
+            gJICTimer =
+                NS_NewTimer(SystemGroup::EventTargetFor(TaskCategory::Other))
+                    .take();
+          }
+          if (gJICTimer) {
+            gJICTimer->InitWithNamedFuncCallback(
+                [](nsITimer*, void*) -> void {
+                  StaticMutexAutoLock locker(gMutex);
+                  SendBatch(locker);
+                },
+                nullptr,
+                mozilla::StaticPrefs::
+                    toolkit_telemetry_geckoview_maxBatchStalenessMS(),
+                nsITimer::TYPE_ONE_SHOT_LOW_PRIORITY,
+                "GeckoviewStreamingTelemetry::SendBatch");
+          }
+        }));
   }
   double batchDurationMs = (TimeStamp::Now() - gBatchBegan).ToMilliseconds();
   if (batchDurationMs >