Bug 1872705: Set a maximum number of recycled canvas buffers. r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D197856

gfx/layers/CanvasDrawEventRecorder.cpp

@@ -37,6 +37,7 @@ static Maybe<ShmemAndHandle> CreateAndMapShmem(size_t aSize) {
 CanvasDrawEventRecorder::CanvasDrawEventRecorder() {
   mDefaultBufferSize = ipc::SharedMemory::PageAlignedSize(
       StaticPrefs::gfx_canvas_remote_default_buffer_size());
+  mMaxDefaultBuffers = StaticPrefs::gfx_canvas_remote_max_default_buffers();
   mMaxSpinCount = StaticPrefs::gfx_canvas_remote_max_spin_count();
   mDropBufferLimit = StaticPrefs::gfx_canvas_remote_drop_buffer_limit();
   mDropBufferOnZero = mDropBufferLimit;
@@ -176,9 +177,25 @@ gfx::ContiguousBuffer& CanvasDrawEventRecorder::GetContiguousBuffer(
     return mCurrentBuffer;
   }
 
-  // If the next recycled buffer is big enough and free use that.
-  if (mRecycledBuffers.front().Capacity() > aSize &&
-      mRecycledBuffers.front().eventCount <= mHeader->processedCount) {
+  bool useRecycledBuffer = false;
+  if (mRecycledBuffers.front().Capacity() > aSize) {
+    // The recycled buffer is big enough, check if it is free.
+    if (mRecycledBuffers.front().eventCount <= mHeader->processedCount) {
+      useRecycledBuffer = true;
+    } else if (mRecycledBuffers.size() >= mMaxDefaultBuffers) {
+      // We've hit he max number of buffers, wait for the next one to be free.
+      // We wait for (eventCount - 1), as we check and signal in the translator
+      // during the play event, before the processedCount has been updated.
+      useRecycledBuffer = true;
+      if (!WaitForCheckpoint(mRecycledBuffers.front().eventCount - 1)) {
+        // The wait failed or we're shutting down, just return an empty buffer.
+        mCurrentBuffer = CanvasBuffer();
+        return mCurrentBuffer;
+      }
+    }
+  }
+
+  if (useRecycledBuffer) {
     // Only queue default size buffers for recycling.
     if (mCurrentBuffer.Capacity() == mDefaultBufferSize) {
       WriteInternalEvent(RECYCLE_BUFFER);

gfx/layers/CanvasDrawEventRecorder.h

@@ -129,6 +129,7 @@ class CanvasDrawEventRecorder final : public gfx::DrawEventRecorderPrivate,
   void CheckAndSignalReader();
 
   size_t mDefaultBufferSize;
+  size_t mMaxDefaultBuffers;
   uint32_t mMaxSpinCount;
   uint32_t mDropBufferLimit;
   uint32_t mDropBufferOnZero;

gfx/layers/ipc/CanvasTranslator.cpp

@@ -227,6 +227,10 @@ void CanvasTranslator::AddBuffer(ipc::SharedMemoryBasic::Handle&& aBufferHandle,
   MOZ_RELEASE_ASSERT(mHeader->readerState == State::Paused);
   MOZ_ASSERT(mDefaultBufferSize != 0);
 
+  // Check and signal the writer when we finish with a buffer, because it
+  // might have hit the buffer count limit and be waiting to use our old one.
+  CheckAndSignalWriter();
+
   // Default sized buffers will have been queued for recycling.
   if (mCurrentShmem.Size() == mDefaultBufferSize) {
     mCanvasShmems.emplace(std::move(mCurrentShmem));
@@ -326,6 +330,10 @@ void CanvasTranslator::RecycleBuffer() {
 }
 
 void CanvasTranslator::NextBuffer() {
+  // Check and signal the writer when we finish with a buffer, because it
+  // might have hit the buffer count limit and be waiting to use our old one.
+  CheckAndSignalWriter();
+
   mCurrentShmem = std::move(mCanvasShmems.front());
   mCanvasShmems.pop();
   mCurrentMemReader = mCurrentShmem.CreateMemReader();

modules/libpref/init/StaticPrefList.yaml

@@ -5741,6 +5741,12 @@
   value: 32 * 1024
   mirror: always
 
+# Maximum number of Default size shmem buffers to use
+- name: gfx.canvas.remote.max_default_buffers
+  type: RelaxedAtomicUint32
+  value: 256
+  mirror: always
+
 # How many times to spin before waiting in remote canvas
 - name: gfx.canvas.remote.max-spin-count
   type: RelaxedAtomicUint32