Bug 1860954 don't store the graph lookup key in the graphs hashtable r=padenot,pehrsons

The necessary values for the lookup are now all in the graph itself.

I suspect this would also be possible with nsTHashtable but HashSet is
designed for a lookup class that differs from the stored class and requires
less boilerplate.

Depends on D191831

Differential Revision: https://phabricator.services.mozilla.com/D191832

dom/media/MediaTrackGraph.cpp

@@ -120,29 +120,34 @@ namespace {
  * A hash table containing the graph instances, one per Window ID,
  * sample rate, and device ID combination.
  */
-class GraphKey final {
- public:
-  GraphKey(uint64_t aWindowID, TrackRate aSampleRate,
-           CubebUtils::AudioDeviceID aOutputDeviceID)
-      : mWindowID(aWindowID),
-        mSampleRate(aSampleRate),
-        mOutputDeviceID(aOutputDeviceID) {}
-  GraphKey(const GraphKey&) = default;
-  ~GraphKey() = default;
-  bool operator==(const GraphKey& b) const {
-    return mWindowID == b.mWindowID && mSampleRate == b.mSampleRate &&
-           mOutputDeviceID == b.mOutputDeviceID;
-  }
-  PLDHashNumber Hash() const {
+struct GraphLookup final {
+  HashNumber Hash() const {
     return HashGeneric(mWindowID, mSampleRate, mOutputDeviceID);
   }
-
- private:
-  uint64_t mWindowID;
-  TrackRate mSampleRate;
-  CubebUtils::AudioDeviceID mOutputDeviceID;
+  const uint64_t mWindowID;
+  const TrackRate mSampleRate;
+  const CubebUtils::AudioDeviceID mOutputDeviceID;
 };
-nsTHashMap<nsGenericHashKey<GraphKey>, MediaTrackGraphImpl*> gGraphs;
+
+struct GraphHasher {  // for HashSet
+  using Lookup = const GraphLookup;
+
+  static HashNumber hash(const Lookup& aLookup) { return aLookup.Hash(); }
+
+  static bool match(const MediaTrackGraphImpl* aGraph, const Lookup& aLookup) {
+    return aGraph->mWindowID == aLookup.mWindowID &&
+           aGraph->GraphRate() == aLookup.mSampleRate &&
+           aGraph->mOutputDeviceID == aLookup.mOutputDeviceID;
+  }
+};
+
+// The weak reference to the graph is removed when its last track is removed.
+using GraphHashSet =
+    HashSet<MediaTrackGraphImpl*, GraphHasher, InfallibleAllocPolicy>;
+GraphHashSet* Graphs() {
+  static GraphHashSet sGraphs(4);  // 4 is minimum HashSet capacity
+  return &sGraphs;
+}
 }  // anonymous namespace
 
 static void ApplyTrackDisabling(DisabledTrackMode aDisabledMode,
@@ -3284,8 +3289,9 @@ MediaTrackGraphImpl* MediaTrackGraphImpl::GetInstanceIfExists(
   MOZ_ASSERT(NS_IsMainThread(), "Main thread only");
   MOZ_ASSERT(aSampleRate > 0);
 
-  GraphKey key(aWindowID, aSampleRate, aOutputDeviceID);
-  return gGraphs.Get(key);
+  GraphHashSet::Ptr p =
+      Graphs()->lookup({aWindowID, aSampleRate, aOutputDeviceID});
+  return p ? *p : nullptr;
 }
 
 // Public method has an nsPIDOMWindowInner* parameter to ensure that the
@@ -3313,31 +3319,31 @@ MediaTrackGraphImpl* MediaTrackGraphImpl::GetInstance(
   MOZ_ASSERT(aGraphDriverRequested != OFFLINE_THREAD_DRIVER,
              "Use CreateNonRealtimeInstance() for offline graphs");
 
-  MediaTrackGraphImpl* graph =
-      GetInstanceIfExists(aWindowID, aSampleRate, aOutputDeviceID);
-
-  if (!graph) {
-    GraphRunType runType = DIRECT_DRIVER;
-    if (Preferences::GetBool("media.audiograph.single_thread.enabled", true)) {
-      runType = SINGLE_THREAD;
-    }
-
-    // In a real time graph, the number of output channels is determined by
-    // the underlying number of channel of the default audio output device, and
-    // capped to 8.
-    uint32_t channelCount =
-        std::min<uint32_t>(8, CubebUtils::MaxNumberOfChannels());
-    graph = new MediaTrackGraphImpl(aGraphDriverRequested, runType, aWindowID,
-                                    aSampleRate, channelCount, aOutputDeviceID,
-                                    aMainThread);
-    GraphKey key(aWindowID, aSampleRate, aOutputDeviceID);
-    gGraphs.InsertOrUpdate(key, graph);
-
-    LOG(LogLevel::Debug,
-        ("Starting up MediaTrackGraph %p for window 0x%" PRIx64, graph,
-         aWindowID));
+  GraphHashSet* graphs = Graphs();
+  GraphHashSet::AddPtr addPtr =
+      graphs->lookupForAdd({aWindowID, aSampleRate, aOutputDeviceID});
+  if (addPtr) {  // graph already exists
+    return *addPtr;
   }
 
+  GraphRunType runType = DIRECT_DRIVER;
+  if (Preferences::GetBool("media.audiograph.single_thread.enabled", true)) {
+    runType = SINGLE_THREAD;
+  }
+
+  // In a real time graph, the number of output channels is determined by
+  // the underlying number of channel of the default audio output device, and
+  // capped to 8.
+  uint32_t channelCount =
+      std::min<uint32_t>(8, CubebUtils::MaxNumberOfChannels());
+  MediaTrackGraphImpl* graph = new MediaTrackGraphImpl(
+      aGraphDriverRequested, runType, aWindowID, aSampleRate, channelCount,
+      aOutputDeviceID, aMainThread);
+  MOZ_ALWAYS_TRUE(graphs->add(addPtr, graph));
+
+  LOG(LogLevel::Debug, ("Starting up MediaTrackGraph %p for window 0x%" PRIx64,
+                        graph, aWindowID));
+
   return graph;
 }
 
@@ -3549,14 +3555,9 @@ void MediaTrackGraph::AddTrack(MediaTrack* aTrack) {
   MediaTrackGraphImpl* graph = static_cast<MediaTrackGraphImpl*>(this);
 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
   if (graph->mRealtime) {
-    bool found = false;
-    for (const auto& currentGraph : gGraphs.Values()) {
-      if (currentGraph == graph) {
-        found = true;
-        break;
-      }
-    }
-    MOZ_DIAGNOSTIC_ASSERT(found, "Graph must not be shutting down");
+    GraphHashSet::Ptr p = Graphs()->lookup(
+        {graph->mWindowID, GraphRate(), graph->mOutputDeviceID});
+    MOZ_DIAGNOSTIC_ASSERT(p, "Graph must not be shutting down");
   }
 #endif
   NS_ADDREF(aTrack);
@@ -3574,12 +3575,11 @@ void MediaTrackGraphImpl::RemoveTrack(MediaTrack* aTrack) {
                          this, aTrack));
     if (mRealtime) {
       // Find the graph in the hash table and remove it.
-      for (auto iter = gGraphs.Iter(); !iter.Done(); iter.Next()) {
-        if (iter.UserData() == this) {
-          iter.Remove();
-          break;
-        }
-      }
+      GraphHashSet* graphs = Graphs();
+      GraphHashSet::Ptr p =
+          graphs->lookup({mWindowID, mSampleRate, mOutputDeviceID});
+      MOZ_ASSERT(*p == this);
+      graphs->remove(p);
     }
     // The graph thread will shut itself down soon, but won't be able to do
     // that if JS continues to run.