Re-land: cc: Implement shared worker contexts.

cc/output/context_provider.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_CONTEXT_PROVIDER_H_
 #define CC_OUTPUT_CONTEXT_PROVIDER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
@@ skipping 14 matching lines @@
 namespace cc {
 struct ManagedMemoryPolicy;
 
 class ContextProvider : public base::RefCountedThreadSafe<ContextProvider> {
  public:
   class ScopedContextLock {
    public:
     explicit ScopedContextLock(ContextProvider* context_provider)
         : context_provider_(context_provider),
           context_lock_(*context_provider_->GetLock()) {
-      // Allow current thread to bind to |context_provider|.
+      // Allow current thread to use |context_provider_|.
       context_provider_->DetachFromThread();
     }
     ~ScopedContextLock() {
-      // Allow a different thread to bind to |context_provider|.
+      // Allow usage by thread for which |context_provider_| is bound to.
       context_provider_->DetachFromThread();
     }
 
     gpu::gles2::GLES2Interface* ContextGL() {
       return context_provider_->ContextGL();
     }
 
    private:
     ContextProvider* const context_provider_;
     base::AutoLock context_lock_;
   };
   // Bind the 3d context to the current thread. This should be called before
   // accessing the contexts. Calling it more than once should have no effect.
   // Once this function has been called, the class should only be accessed
-  // from the same thread.
+  // from the same thread unless the function has some explicitly specified
+  // rules for access on a different thread. See SetupLockOnMainThread(), which
+  // can be used to provide access from multiple threads.
   virtual bool BindToCurrentThread() = 0;
   virtual void DetachFromThread() {}
 
   virtual gpu::gles2::GLES2Interface* ContextGL() = 0;
   virtual gpu::ContextSupport* ContextSupport() = 0;
   virtual class GrContext* GrContext() = 0;
 
   struct Capabilities {
     gpu::Capabilities gpu;
     size_t max_transfer_buffer_usage_bytes;
 
     CC_EXPORT Capabilities();
   };
 
   // Invalidates the cached OpenGL state in GrContext.
   // See skia GrContext::resetContext for details.
   virtual void InvalidateGrContext(uint32_t state) = 0;
 
-  // Sets up a lock so this context can be used from multiple threads.
+  // Sets up a lock so this context can be used from multiple threads. After
+  // calling this, all functions without explicit thread usage constraints can
+  // be used on any thread while the lock returned by GetLock() is acquired.
   virtual void SetupLock() = 0;
 
   // Returns the lock that should be held if using this context from multiple
-  // threads.
+  // threads. This can be called on any thread.
   virtual base::Lock* GetLock() = 0;
 
   // Returns the capabilities of the currently bound 3d context.
   virtual Capabilities ContextCapabilities() = 0;
 
   // Ask the provider to check if the contexts are valid or lost. If they are,
   // this should invalidate the provider so that it can be replaced with a new
   // one.
   virtual void VerifyContexts() = 0;
 
@@ skipping 20 matching lines @@
       const MemoryPolicyChangedCallback& memory_policy_changed_callback) = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<ContextProvider>;
   virtual ~ContextProvider() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_CONTEXT_PROVIDER_H_