Idle cleanup for worker context

cc/output/context_cache_controller.h

Index: cc/output/context_cache_controller.h
diff --git a/cc/output/context_cache_controller.h b/cc/output/context_cache_controller.h
index 03f7e2cd74f9117e11cb95ac6db4a747199301f7..357e5daacb5862f0863492625804ec1e8c7353bc 100644
--- a/cc/output/context_cache_controller.h
+++ b/cc/output/context_cache_controller.h
@@ -10,11 +10,13 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
 #include "cc/base/cc_export.h"
 
 class GrContext;
 
 namespace base {
+class Lock;
 class SingleThreadTaskRunner;
 }
 
@@ -25,26 +27,26 @@ class ContextSupport;
 namespace cc {
 
 // ContextCacheController manages clearing cached data on ContextProvider when
-// appropriate. Currently, cache clearing happens when the ContextProvider
-// transitions from visible to not visible. As a ContextProvider may have
-// multiple clients, ContextCacheController tracks visibility across all
-// clients and only cleans up when appropriate.
-//
-// Note: Virtuals on this function are for testing only. This function is not
-// designed to have multiple implementations.
+// appropriate. Currently, cache clearing is triggered when the Context
+// provider transitions from Visible to Not Visible, or from Busy to Idle. As a
+// ContextProvider may have multiple clients, ContextCacheController tracks
+// visibility and idle status across all clients and only cleans up when
+// appropriate.
 class CC_EXPORT ContextCacheController {
  public:
-  class CC_EXPORT ScopedVisibility {
+  class CC_EXPORT ScopedToken {
    public:
-    ~ScopedVisibility();
+    ~ScopedToken();
 
    private:
     friend class ContextCacheController;
-    ScopedVisibility();
+    ScopedToken();
     void Release();
 
     bool released_ = false;
   };
+  using ScopedVisibility = ScopedToken;
+  using ScopedBusy = ScopedToken;
 
   ContextCacheController(
       gpu::ContextSupport* context_support,
@@ -52,6 +54,7 @@ class CC_EXPORT ContextCacheController {
   virtual ~ContextCacheController();
 
   void SetGrContext(GrContext* gr_context);
+  void SetLock(base::Lock* lock);
 
   // Clients of the owning ContextProvider should call this function when they
   // become visible. The returned ScopedVisibility pointer must be passed back
@@ -64,17 +67,42 @@ class CC_EXPORT ContextCacheController {
   virtual void ClientBecameNotVisible(
       std::unique_ptr<ScopedVisibility> scoped_visibility);
 
- protected:
-  std::unique_ptr<ScopedVisibility> CreateScopedVisibilityForTesting() const;
-  void ReleaseScopedVisibilityForTesting(
-      std::unique_ptr<ScopedVisibility> scoped_visibility) const;
+  // Clients of the owning ContextProvider may call this function when they
+  // become busy. The returned ScopedBusy pointer must be passed back
+  // to ClientBecameNotBusy or it will DCHECK in its destructor.
+  std::unique_ptr<ScopedBusy> ClientBecameBusy();
+
+  // When a client becomes not busy, it must pass back any ScopedBusy
+  // pointers it owns via this function.
+  void ClientBecameNotBusy(std::unique_ptr<ScopedBusy> scoped_busy);
 
  private:
+  void OnIdle(uint32_t idle_generation);
+  void PostIdleCallback(uint32_t current_idle_generation) const;
+  void InvalidatePendingIdleCallbacks();
+
   gpu::ContextSupport* context_support_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   GrContext* gr_context_ = nullptr;
 
+  // If set, |context_lock_| must be held before accessing any member within
+  // the idle callback. Exceptions to this are |current_idle_generation_|,
+  // which has its own lock, and weak_ptr_ and task_runner_, which may be
+  // accessed from multiple threads without locking.
+  base::Lock* context_lock_ = nullptr;
+
   uint32_t num_clients_visible_ = 0;
+  uint32_t num_clients_busy_ = 0;
+  bool callback_pending_ = false;
+
+  // |current_idle_generation_lock_| must be held when accessing
+  // |current_idle_generation_|. |current_idle_generation_lock_| must never be
+  // held while acquiring |context_lock_|.
+  base::Lock current_idle_generation_lock_;
+  uint32_t current_idle_generation_ = 0;
+
+  base::WeakPtr<ContextCacheController> weak_ptr_;
+  base::WeakPtrFactory<ContextCacheController> weak_factory_;
 };
 
 }  // namespace cc