Bug 1852145 - Part 1. Refactor CanvasRenderThread to represent a virtual thread. r=gfx-reviewers,lsalzman

Prior to this patch, CanvasRenderThread represents the concrete thread
we would spawn if gfxVars::UseCanvasRenderThread() returned true.
CanvasManagerParent was responsible for checking our state and deciding
between using the Compositor, Renderer and CanvasRender threads.

This patch makes the CanvasRenderThread class represent a virtual
thread. It will spawn a CanvasRender thread if necessary. Other classes
may use the abstraction to run on the correct thread without having to
duplicate the selection logic.

Differential Revision: https://phabricator.services.mozilla.com/D187719

gfx/ipc/CanvasManagerParent.cpp

@@ -13,7 +13,6 @@
 #include "mozilla/ipc/Endpoint.h"
 #include "mozilla/layers/CompositorThread.h"
 #include "mozilla/webgpu/WebGPUParent.h"
-#include "mozilla/webrender/RenderThread.h"
 #include "nsIThread.h"
 #include "nsThreadUtils.h"
 
@@ -27,41 +26,21 @@ CanvasManagerParent::ManagerSet CanvasManagerParent::sManagers;
 
   auto manager = MakeRefPtr<CanvasManagerParent>();
 
-  if (!gfxVars::SupportsThreadsafeGL()) {
-    nsCOMPtr<nsIThread> owningThread;
-    owningThread = wr::RenderThread::GetRenderThread();
-    MOZ_ASSERT(owningThread);
+  nsCOMPtr<nsIThread> owningThread =
+      gfx::CanvasRenderThread::GetCanvasRenderThread();
+  MOZ_ASSERT(owningThread);
 
-    owningThread->Dispatch(NewRunnableMethod<Endpoint<PCanvasManagerParent>&&>(
-        "CanvasManagerParent::Bind", manager, &CanvasManagerParent::Bind,
-        std::move(aEndpoint)));
-  } else if (gfxVars::UseCanvasRenderThread()) {
-    nsCOMPtr<nsIThread> owningThread;
-    owningThread = gfx::CanvasRenderThread::GetCanvasRenderThread();
-    MOZ_ASSERT(owningThread);
-
-    owningThread->Dispatch(NewRunnableMethod<Endpoint<PCanvasManagerParent>&&>(
-        "CanvasManagerParent::Bind", manager, &CanvasManagerParent::Bind,
-        std::move(aEndpoint)));
-  } else {
-    manager->Bind(std::move(aEndpoint));
-  }
+  owningThread->Dispatch(NewRunnableMethod<Endpoint<PCanvasManagerParent>&&>(
+      "CanvasManagerParent::Bind", manager, &CanvasManagerParent::Bind,
+      std::move(aEndpoint)));
 }
 
 /* static */ void CanvasManagerParent::Shutdown() {
   MOZ_ASSERT(NS_IsMainThread());
 
-  nsCOMPtr<nsISerialEventTarget> owningThread;
-  if (!gfxVars::SupportsThreadsafeGL()) {
-    owningThread = wr::RenderThread::GetRenderThread();
-  } else if (gfxVars::UseCanvasRenderThread()) {
-    owningThread = gfx::CanvasRenderThread::GetCanvasRenderThread();
-  } else {
-    owningThread = layers::CompositorThread();
-  }
-  if (!owningThread) {
-    return;
-  }
+  nsCOMPtr<nsIThread> owningThread =
+      gfx::CanvasRenderThread::GetCanvasRenderThread();
+  MOZ_ASSERT(owningThread);
 
   NS_DispatchAndSpinEventLoopUntilComplete(
       "CanvasManagerParent::Shutdown"_ns, owningThread,

gfx/ipc/CanvasRenderThread.cpp

@@ -7,6 +7,10 @@
 #include "CanvasRenderThread.h"
 
 #include "mozilla/BackgroundHangMonitor.h"
+#include "mozilla/gfx/CanvasManagerParent.h"
+#include "mozilla/gfx/gfxVars.h"
+#include "mozilla/layers/CompositorThread.h"
+#include "mozilla/webrender/RenderThread.h"
 #include "transport/runnable_utils.h"
 
 namespace mozilla::gfx {
@@ -17,13 +21,11 @@ static mozilla::BackgroundHangMonitor* sBackgroundHangMonitor;
 static bool sCanvasRenderThreadEverStarted = false;
 #endif
 
-CanvasRenderThread::CanvasRenderThread(RefPtr<nsIThread> aThread)
-    : mThread(std::move(aThread)) {}
+CanvasRenderThread::CanvasRenderThread(nsCOMPtr<nsIThread>&& aThread,
+                                       bool aCreatedThread)
+    : mThread(std::move(aThread)), mCreatedThread(aCreatedThread) {}
 
-CanvasRenderThread::~CanvasRenderThread() {}
-
-// static
-CanvasRenderThread* CanvasRenderThread::Get() { return sCanvasRenderThread; }
+CanvasRenderThread::~CanvasRenderThread() = default;
 
 // static
 void CanvasRenderThread::Start() {
@@ -37,6 +39,21 @@ void CanvasRenderThread::Start() {
   sCanvasRenderThreadEverStarted = true;
 #endif
 
+  nsCOMPtr<nsIThread> thread;
+  if (!gfxVars::SupportsThreadsafeGL()) {
+    thread = wr::RenderThread::GetRenderThread();
+    MOZ_ASSERT(thread);
+  } else if (!gfxVars::UseCanvasRenderThread()) {
+    thread = layers::CompositorThread();
+    MOZ_ASSERT(thread);
+  }
+
+  if (thread) {
+    sCanvasRenderThread =
+        new CanvasRenderThread(std::move(thread), /* aCreatedThread */ false);
+    return;
+  }
+
   // This is 4M, which is higher than the default 256K.
   // Increased with bug 1753349 to accommodate the `chromium/5359` branch of
   // ANGLE, which has large peak stack usage for some pathological shader
@@ -51,7 +68,6 @@ void CanvasRenderThread::Start() {
   const uint32_t stackSize =
       nsIThreadManager::DEFAULT_STACK_SIZE ? 4096 << 10 : 0;
 
-  RefPtr<nsIThread> thread;
   nsresult rv = NS_NewNamedThread(
       "CanvasRenderer", getter_AddRefs(thread),
       NS_NewRunnableFunction(
@@ -75,26 +91,41 @@ void CanvasRenderThread::Start() {
           }),
       {.stackSize = stackSize});
 
-  if (NS_FAILED(rv)) {
+  if (NS_WARN_IF(NS_FAILED(rv))) {
     return;
   }
 
-  sCanvasRenderThread = new CanvasRenderThread(thread);
+  sCanvasRenderThread =
+      new CanvasRenderThread(std::move(thread), /* aCreatedThread */ true);
 }
 
 // static
-void CanvasRenderThread::ShutDown() {
+void CanvasRenderThread::Shutdown() {
   MOZ_ASSERT(NS_IsMainThread());
-  MOZ_ASSERT(sCanvasRenderThread);
+
+  // It is possible we never initialized this thread in the parent process,
+  // because we used the GPU process instead.
+  if (!sCanvasRenderThread) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    return;
+  }
+
+  CanvasManagerParent::Shutdown();
 
   // Null out sCanvasRenderThread before we enter synchronous Shutdown,
   // from here on we are to be considered shut down for our consumers.
-  nsCOMPtr<nsIThread> oldThread = sCanvasRenderThread->GetCanvasRenderThread();
+  nsCOMPtr<nsIThread> oldThread;
+  if (sCanvasRenderThread->mCreatedThread) {
+    oldThread = sCanvasRenderThread->GetCanvasRenderThread();
+    MOZ_ASSERT(oldThread);
+  }
   sCanvasRenderThread = nullptr;
 
-  // We do a synchronous shutdown here while spinning the MT event loop.
-  MOZ_ASSERT(oldThread);
-  oldThread->Shutdown();
+  // We do a synchronous shutdown here while spinning the MT event loop, but
+  // only if we created a dedicated CanvasRender thread.
+  if (oldThread) {
+    oldThread->Shutdown();
+  }
 }
 
 // static

gfx/ipc/CanvasRenderThread.h

@@ -13,22 +13,28 @@
 #include "nsISupportsImpl.h"
 #include "nsThread.h"
 
+class nsIRunnable;
+
 namespace mozilla::gfx {
 
+/**
+ * This class represents the virtual thread for canvas rendering. Depending on
+ * platform requirements and user configuration, canvas rendering may happen on
+ * the Compositor thread, Render thread or the CanvasRender thread.
+ */
 class CanvasRenderThread final {
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_MAIN_THREAD(
       CanvasRenderThread)
 
  public:
-  /// Can be called from any thread, may return nullptr late in shutdown.
-  static CanvasRenderThread* Get();
-
   /// Can only be called from the main thread, expected to be called at most
-  /// once during a process' lifetime.
+  /// once during a process' lifetime. Must be called after the Compositor and
+  /// Render threads are initialized.
   static void Start();
 
-  /// Can only be called from the main thread.
-  static void ShutDown();
+  /// Can only be called from the main thread. Must be called before the
+  /// Compositor and Render threads are shutdown.
+  static void Shutdown();
 
   /// Can be called from any thread.
   static bool IsInCanvasRenderThread();
@@ -37,12 +43,16 @@ class CanvasRenderThread final {
   static already_AddRefed<nsIThread> GetCanvasRenderThread();
 
  private:
-  explicit CanvasRenderThread(RefPtr<nsIThread> aThread);
+  CanvasRenderThread(nsCOMPtr<nsIThread>&& aThread, bool aCreatedThread);
   ~CanvasRenderThread();
 
   void PostRunnable(already_AddRefed<nsIRunnable> aRunnable);
 
-  RefPtr<nsIThread> const mThread;
+  nsCOMPtr<nsIThread> const mThread;
+
+  // True if mThread points to CanvasRender thread, false if mThread points to
+  // Compositor/Render thread.
+  bool mCreatedThread;
 };
 
 }  // namespace mozilla::gfx

gfx/ipc/GPUParent.cpp

@@ -14,7 +14,6 @@
 #include "GPUProcessManager.h"
 #include "gfxGradientCache.h"
 #include "GfxInfoBase.h"
-#include "CanvasManagerParent.h"
 #include "VRGPUChild.h"
 #include "VRManager.h"
 #include "VRManagerParent.h"
@@ -378,10 +377,8 @@ mozilla::ipc::IPCResult GPUParent::RecvInit(
 #endif
 
   // Make sure to do this *after* we update gfxVars above.
-  if (gfxVars::UseCanvasRenderThread()) {
-    gfx::CanvasRenderThread::Start();
-  }
   wr::RenderThread::Start(aWrNamespace);
+  gfx::CanvasRenderThread::Start();
   image::ImageMemoryReporter::InitForWebRender();
 
   VRManager::ManagerInit();
@@ -700,9 +697,10 @@ void GPUParent::ActorDestroy(ActorDestroyReason aWhy) {
           self->mVsyncBridge = nullptr;
         }
         VideoBridgeParent::Shutdown();
-        // This could be running on either the Compositor or the Renderer
-        // thread.
-        CanvasManagerParent::Shutdown();
+        // This could be running on either the Compositor thread, the Renderer
+        // thread, or the dedicated CanvasRender thread, so we need to shutdown
+        // before the former two.
+        CanvasRenderThread::Shutdown();
         CompositorThreadHolder::Shutdown();
         RemoteTextureMap::Shutdown();
         // There is a case that RenderThread exists when gfxVars::UseWebRender()
@@ -711,9 +709,6 @@ void GPUParent::ActorDestroy(ActorDestroyReason aWhy) {
         if (wr::RenderThread::Get()) {
           wr::RenderThread::ShutDown();
         }
-        if (gfx::CanvasRenderThread::Get()) {
-          gfx::CanvasRenderThread::ShutDown();
-        }
 #ifdef XP_WIN
         if (widget::WinCompositorWindowThread::Get()) {
           widget::WinCompositorWindowThread::ShutDown();

gfx/layers/ipc/CompositorThread.cpp

@@ -28,7 +28,7 @@ static Atomic<bool> sFinishedCompositorShutDown(false);
 static mozilla::BackgroundHangMonitor* sBackgroundHangMonitor;
 static ProfilerThreadId sProfilerThreadId;
 
-nsISerialEventTarget* CompositorThread() {
+nsIThread* CompositorThread() {
   return sCompositorThreadHolder
              ? sCompositorThreadHolder->GetCompositorThread()
              : nullptr;

gfx/layers/ipc/CompositorThread.h

@@ -13,7 +13,6 @@ namespace mozilla::baseprofiler {
 class BaseProfilerThreadId;
 }
 using ProfilerThreadId = mozilla::baseprofiler::BaseProfilerThreadId;
-class nsISerialEventTarget;
 class nsIThread;
 
 namespace mozilla {
@@ -26,9 +25,7 @@ class CompositorThreadHolder final {
  public:
   CompositorThreadHolder();
 
-  nsISerialEventTarget* GetCompositorThread() const {
-    return mCompositorThread;
-  }
+  nsIThread* GetCompositorThread() const { return mCompositorThread; }
 
   static CompositorThreadHolder* GetSingleton();
 
@@ -61,7 +58,7 @@ class CompositorThreadHolder final {
   friend class CompositorBridgeParent;
 };
 
-nsISerialEventTarget* CompositorThread();
+nsIThread* CompositorThread();
 
 }  // namespace layers
 }  // namespace mozilla

gfx/thebes/gfxPlatform.cpp

@@ -22,7 +22,6 @@
 #include "mozilla/gfx/GPUProcessManager.h"
 #include "mozilla/gfx/GraphicsMessages.h"
 #include "mozilla/gfx/CanvasManagerChild.h"
-#include "mozilla/gfx/CanvasManagerParent.h"
 #include "mozilla/gfx/CanvasRenderThread.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/DebugOnly.h"
@@ -1309,14 +1308,15 @@ void gfxPlatform::InitLayersIPC() {
 #endif
     if (!gfxConfig::IsEnabled(Feature::GPU_PROCESS)) {
       RemoteTextureMap::Init();
-      if (gfxVars::UseCanvasRenderThread()) {
-        gfx::CanvasRenderThread::Start();
-      }
       wr::RenderThread::Start(GPUProcessManager::Get()->AllocateNamespace());
       image::ImageMemoryReporter::InitForWebRender();
     }
 
     layers::CompositorThreadHolder::Start();
+
+    if (!gfxConfig::IsEnabled(Feature::GPU_PROCESS)) {
+      gfx::CanvasRenderThread::Start();
+    }
   }
 }
 
@@ -1343,8 +1343,10 @@ void gfxPlatform::ShutdownLayersIPC() {
     gfx::CanvasManagerChild::Shutdown();
     layers::CompositorManagerChild::Shutdown();
     layers::ImageBridgeChild::ShutDown();
-    // This could be running on either the Compositor or the Renderer thread.
-    gfx::CanvasManagerParent::Shutdown();
+    // This could be running on either the Compositor thread, the Renderer
+    // thread, or the dedicated CanvasRender thread, so we need to shutdown
+    // before the former two.
+    gfx::CanvasRenderThread::Shutdown();
     // This has to happen after shutting down the child protocols.
     layers::CompositorThreadHolder::Shutdown();
     RemoteTextureMap::Shutdown();
@@ -1363,9 +1365,6 @@ void gfxPlatform::ShutdownLayersIPC() {
           nsDependentCString(
               StaticPrefs::GetPrefName_gfx_webrender_blob_tile_size()));
     }
-    if (gfx::CanvasRenderThread::Get()) {
-      gfx::CanvasRenderThread::ShutDown();
-    }
 #if defined(XP_WIN)
     widget::WinWindowOcclusionTracker::ShutDown();
 #endif
@@ -3851,12 +3850,10 @@ void gfxPlatform::DisableGPUProcess() {
   }
 
   RemoteTextureMap::Init();
-  if (gfxVars::UseCanvasRenderThread()) {
-    gfx::CanvasRenderThread::Start();
-  }
   // We need to initialize the parent process to prepare for WebRender if we
   // did not end up disabling it, despite losing the GPU process.
   wr::RenderThread::Start(GPUProcessManager::Get()->AllocateNamespace());
+  gfx::CanvasRenderThread::Start();
   image::ImageMemoryReporter::InitForWebRender();
 }