cc: Add mailbox support to ResourceProvider write locks.

cc/resources/resource_provider.cc

 // Copyright 2012 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.
 
 #include "cc/resources/resource_provider.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 677 matching lines @@
     return;
   } else {
     DeleteResourceInternal(it, NORMAL);
   }
 }
 
 void ResourceProvider::DeleteResourceInternal(ResourceMap::iterator it,
                                               DeleteStyle style) {
   TRACE_EVENT0("cc", "ResourceProvider::DeleteResourceInternal");
   Resource* resource = &it->second;
-  bool lost_resource = resource->lost;
+  DCHECK(resource->exported_count == 0 || style != NORMAL);
 
-  DCHECK(resource->exported_count == 0 || style != NORMAL);
-  if (style == FOR_SHUTDOWN && resource->exported_count > 0)
-    lost_resource = true;
+  bool lost_resource =
+      resource->lost ||
+      (style == FOR_SHUTDOWN && resource->exported_count > 0) ||

[ericrk, 2016/06/14 22:36:05]

nit: It might be nice to break this into a couple bools with some explanation of
what each scenario means.

[sunnyps, 2016/06/14 23:22:51]

Done.

+      (IsGpuResourceType(resource->type) && lost_output_surface_);
+
+  if (!lost_resource &&
+      resource->synchronization_state() == Resource::NEEDS_WAIT) {
+    DCHECK(resource->allocated);
+    DCHECK(IsGpuResourceType(resource->type));
+    GLES2Interface* gl = ContextGL();
+    DCHECK(gl);
+    resource->WaitSyncToken(gl);
+  }
 
   if (resource->image_id) {
     DCHECK(resource->origin == Resource::INTERNAL);
     GLES2Interface* gl = ContextGL();
     DCHECK(gl);
     gl->DestroyImageCHROMIUM(resource->image_id);
   }
   if (resource->gl_upload_query_id) {
     DCHECK(resource->origin == Resource::INTERNAL);
     GLES2Interface* gl = ContextGL();
@@ skipping 10 matching lines @@
     DCHECK(resource->origin == Resource::INTERNAL);
     GLES2Interface* gl = ContextGL();
     DCHECK(gl);
     gl->DeleteBuffers(1, &resource->gl_pixel_buffer_id);
   }
   if (resource->origin == Resource::EXTERNAL) {
     DCHECK(resource->mailbox().IsValid());
     gpu::SyncToken sync_token = resource->mailbox().sync_token();
     if (IsGpuResourceType(resource->type)) {
       DCHECK(resource->mailbox().IsTexture());
-      lost_resource |= lost_output_surface_;
       GLES2Interface* gl = ContextGL();
       DCHECK(gl);
       if (resource->gl_id) {
         gl->DeleteTextures(1, &resource->gl_id);
         resource->gl_id = 0;
         if (!lost_resource) {
           const GLuint64 fence_sync = gl->InsertFenceSyncCHROMIUM();
           gl->ShallowFlushCHROMIUM();
           gl->GenSyncTokenCHROMIUM(fence_sync, sync_token.GetData());
         }
@@ skipping 65 matching lines @@
     DCHECK(resource->allocated);
     DCHECK_EQ(RGBA_8888, resource->format);
     SkImageInfo source_info =
         SkImageInfo::MakeN32Premul(image_size.width(), image_size.height());
     size_t image_stride = image_size.width() * 4;
 
     ScopedWriteLockSoftware lock(this, id);
     SkCanvas dest(lock.sk_bitmap());
     dest.writePixels(source_info, image, image_stride, 0, 0);
   } else {
-    ScopedWriteLockGL lock(this, id);
-    DCHECK(lock.texture_id());
+    ScopedWriteLockGL lock(this, id, false);
+    unsigned resource_texture_id = lock.texture_id();
+    DCHECK(resource_texture_id);
     GLES2Interface* gl = ContextGL();
     DCHECK(gl);
-    gl->BindTexture(resource->target, lock.texture_id());
+    gl->BindTexture(resource->target, resource_texture_id);
     if (resource->format == ETC1) {
       DCHECK_EQ(resource->target, static_cast<GLenum>(GL_TEXTURE_2D));
       int image_bytes = ResourceUtil::CheckedSizeInBytes<int>(image_size, ETC1);
       gl->CompressedTexImage2D(resource->target, 0, GLInternalFormat(ETC1),
                                image_size.width(), image_size.height(), 0,
                                image_bytes, image);
     } else {
       gl->TexSubImage2D(resource->target, 0, 0, 0, image_size.width(),
                         image_size.height(), GLDataFormat(resource->format),
                         GLDataType(resource->format), image);
     }
     const uint64_t fence_sync = gl->InsertFenceSyncCHROMIUM();
     gl->OrderingBarrierCHROMIUM();
     gpu::SyncToken sync_token;
     gl->GenUnverifiedSyncTokenCHROMIUM(fence_sync, sync_token.GetData());
-    lock.UpdateResourceSyncToken(sync_token);
+    lock.set_sync_token(sync_token);
+    lock.set_synchronized(true);
   }
 }
 
 void ResourceProvider::GenerateSyncTokenForResource(ResourceId resource_id) {
   Resource* resource = GetResource(resource_id);
   if (!resource->needs_sync_token())
     return;
 
   gpu::SyncToken sync_token;
   GLES2Interface* gl = ContextGL();
   DCHECK(gl);
 
   const uint64_t fence_sync = gl->InsertFenceSyncCHROMIUM();
   gl->OrderingBarrierCHROMIUM();
   gl->GenUnverifiedSyncTokenCHROMIUM(fence_sync, sync_token.GetData());
 
   resource->UpdateSyncToken(sync_token);
+  resource->SetSynchronized();
 }
 
 void ResourceProvider::GenerateSyncTokenForResources(
     const ResourceIdArray& resource_ids) {
   gpu::SyncToken sync_token;
   bool created_sync_token = false;
   for (ResourceId id : resource_ids) {
     Resource* resource = GetResource(id);
     if (resource->needs_sync_token()) {
       if (!created_sync_token) {
         GLES2Interface* gl = ContextGL();
         DCHECK(gl);
 
         const uint64_t fence_sync = gl->InsertFenceSyncCHROMIUM();
         gl->OrderingBarrierCHROMIUM();
         gl->GenUnverifiedSyncTokenCHROMIUM(fence_sync, sync_token.GetData());
         created_sync_token = true;
       }
 
       resource->UpdateSyncToken(sync_token);
+      resource->SetSynchronized();
     }
   }
 }
 
 ResourceProvider::Resource* ResourceProvider::InsertResource(
     ResourceId id,
     Resource resource) {
   std::pair<ResourceMap::iterator, bool> result =
       resources_.insert(ResourceMap::value_type(id, std::move(resource)));
   DCHECK(result.second);
@@ skipping 88 matching lines @@
       ResourceIdArray unused;
       unused.push_back(id);
       DeleteAndReturnUnusedResourcesToChild(child_it, NORMAL, unused);
     }
   }
 }
 
 ResourceProvider::Resource* ResourceProvider::LockForWrite(ResourceId id) {
   Resource* resource = GetResource(id);
   DCHECK(CanLockForWrite(id));
-  DCHECK_NE(Resource::NEEDS_WAIT, resource->synchronization_state());
+  if (resource->allocated)
+    WaitSyncTokenIfNeeded(id);
   resource->locked_for_write = true;
   resource->SetLocallyUsed();
   return resource;
 }
 
 bool ResourceProvider::CanLockForWrite(ResourceId id) {
   Resource* resource = GetResource(id);
   return !resource->locked_for_write && !resource->lock_for_read_count &&
          !resource->exported_count && resource->origin == Resource::INTERNAL &&
          !resource->lost && ReadLockFenceHasPassed(resource);
 }
 
 bool ResourceProvider::IsOverlayCandidate(ResourceId id) {
   Resource* resource = GetResource(id);
   return resource->is_overlay_candidate;
 }
 
-void ResourceProvider::UnlockForWrite(ResourceProvider::Resource* resource) {
+void ResourceProvider::UnlockForWrite(Resource* resource) {
   DCHECK(resource->locked_for_write);
   DCHECK_EQ(resource->exported_count, 0);
   DCHECK(resource->origin == Resource::INTERNAL);
   resource->locked_for_write = false;
-  resource->SetSynchronized();
 }
 
 void ResourceProvider::EnableReadLockFencesForTesting(ResourceId id) {
   Resource* resource = GetResource(id);
   DCHECK(resource);
   resource->read_lock_fences_enabled = true;
 }
 
 ResourceProvider::ScopedReadLockGL::ScopedReadLockGL(
     ResourceProvider* resource_provider,
     ResourceId resource_id)
-    : resource_provider_(resource_provider),
-      resource_id_(resource_id),
-      resource_(resource_provider->LockForRead(resource_id, false)) {
-  DCHECK(resource_);
+    : resource_provider_(resource_provider), resource_id_(resource_id) {
+  const Resource* resource = resource_provider->LockForRead(resource_id, false);
+  texture_id_ = resource->gl_id;
+  target_ = resource->target;
+  size_ = resource->size;
 }
 
 ResourceProvider::ScopedReadLockGL::~ScopedReadLockGL() {
   resource_provider_->UnlockForRead(resource_id_);
 }
 
 ResourceProvider::ScopedSamplerGL::ScopedSamplerGL(
     ResourceProvider* resource_provider,
     ResourceId resource_id,
     GLenum filter)
-    : ScopedReadLockGL(resource_provider, resource_id),
+    : resource_lock_(resource_provider, resource_id),
       unit_(GL_TEXTURE0),
-      target_(resource_provider->BindForSampling(resource_id, unit_, filter)) {
-}
+      target_(resource_provider->BindForSampling(resource_id, unit_, filter)) {}
 
 ResourceProvider::ScopedSamplerGL::ScopedSamplerGL(
     ResourceProvider* resource_provider,
     ResourceId resource_id,
     GLenum unit,
     GLenum filter)
-    : ScopedReadLockGL(resource_provider, resource_id),
+    : resource_lock_(resource_provider, resource_id),
       unit_(unit),
-      target_(resource_provider->BindForSampling(resource_id, unit_, filter)) {
-}
+      target_(resource_provider->BindForSampling(resource_id, unit_, filter)) {}
 
 ResourceProvider::ScopedSamplerGL::~ScopedSamplerGL() {
 }
 
 ResourceProvider::ScopedWriteLockGL::ScopedWriteLockGL(
     ResourceProvider* resource_provider,
-    ResourceId resource_id)
+    ResourceId resource_id,
+    bool create_mailbox)
     : resource_provider_(resource_provider),
-      resource_(resource_provider->LockForWrite(resource_id)),
-      texture_id_(0),
-      set_sync_token_(false) {
-  resource_provider_->LazyAllocate(resource_);
-  texture_id_ = resource_->gl_id;
-  DCHECK(texture_id_);
-  if (resource_->image_id && resource_->dirty_image)
-    resource_provider_->BindImageForSampling(resource_);
+      resource_id_(resource_id),
+      synchronized_(false) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  Resource* resource = resource_provider->LockForWrite(resource_id);
+  resource_provider_->LazyAllocate(resource);
+  if (resource->image_id && resource->dirty_image)
+    resource_provider_->BindImageForSampling(resource);
+  if (create_mailbox) {
+    resource_provider_->CreateMailboxAndBindResource(
+        resource_provider_->ContextGL(), resource);
+  }
+  texture_id_ = resource->gl_id;
+  target_ = resource->target;
+  format_ = resource->format;
+  size_ = resource->size;
+  mailbox_ = resource->mailbox();
 }
 
 ResourceProvider::ScopedWriteLockGL::~ScopedWriteLockGL() {
-  if (set_sync_token_)
-    resource_->UpdateSyncToken(sync_token_);
-  resource_provider_->UnlockForWrite(resource_);
+  DCHECK(thread_checker_.CalledOnValidThread());
+  Resource* resource = resource_provider_->GetResource(resource_id_);
+  DCHECK(resource->locked_for_write);
+  if (sync_token_.HasData())
+    resource->UpdateSyncToken(sync_token_);
+  if (synchronized_)
+    resource->SetSynchronized();
+  resource_provider_->UnlockForWrite(resource);
+}
+
+ResourceProvider::ScopedTextureProvider::ScopedTextureProvider(
+    gpu::gles2::GLES2Interface* gl,
+    ScopedWriteLockGL* resource_lock,
+    bool use_mailbox)
+    : gl_(gl), use_mailbox_(use_mailbox) {
+  if (use_mailbox_) {
+    texture_id_ = gl_->CreateAndConsumeTextureCHROMIUM(
+        resource_lock->target(), resource_lock->mailbox().name());
+  } else {
+    texture_id_ = resource_lock->texture_id();
+  }
+  DCHECK(texture_id_);
+}
+
+ResourceProvider::ScopedTextureProvider::~ScopedTextureProvider() {
+  if (use_mailbox_)
+    gl_->DeleteTextures(1, &texture_id_);
+}
+
+ResourceProvider::ScopedSkSurfaceProvider::ScopedSkSurfaceProvider(
+    ContextProvider* context_provider,
+    ScopedWriteLockGL* resource_lock,
+    bool use_mailbox,
+    bool use_distance_field_text,
+    bool can_use_lcd_text,
+    int msaa_sample_count)
+    : texture_provider_(context_provider->ContextGL(),
+                        resource_lock,
+                        use_mailbox) {
+  GrGLTextureInfo texture_info;
+  texture_info.fID = texture_provider_.texture_id();
+  texture_info.fTarget = resource_lock->target();
+  GrBackendTextureDesc desc;
+  desc.fFlags = kRenderTarget_GrBackendTextureFlag;
+  desc.fWidth = resource_lock->size().width();
+  desc.fHeight = resource_lock->size().height();
+  desc.fConfig = ToGrPixelConfig(resource_lock->format());
+  desc.fOrigin = kTopLeft_GrSurfaceOrigin;
+  desc.fTextureHandle = skia::GrGLTextureInfoToGrBackendObject(texture_info);
+  desc.fSampleCnt = msaa_sample_count;
+
+  uint32_t flags =
+      use_distance_field_text ? SkSurfaceProps::kUseDistanceFieldFonts_Flag : 0;
+  // Use unknown pixel geometry to disable LCD text.
+  SkSurfaceProps surface_props(flags, kUnknown_SkPixelGeometry);
+  if (can_use_lcd_text) {
+    // LegacyFontHost will get LCD text and skia figures out what type to use.
+    surface_props =
+        SkSurfaceProps(flags, SkSurfaceProps::kLegacyFontHost_InitType);
+  }
+  sk_surface_ = SkSurface::MakeFromBackendTextureAsRenderTarget(
+      context_provider->GrContext(), desc, &surface_props);
+}
+
+ResourceProvider::ScopedSkSurfaceProvider::~ScopedSkSurfaceProvider() {
+  if (sk_surface_.get()) {
+    sk_surface_->prepareForExternalIO();
+    sk_surface_.reset();
+  }
 }
 
 void ResourceProvider::PopulateSkBitmapWithResource(
     SkBitmap* sk_bitmap, const Resource* resource) {
   DCHECK_EQ(RGBA_8888, resource->format);
   SkImageInfo info = SkImageInfo::MakeN32Premul(resource->size.width(),
                                                 resource->size.height());
   sk_bitmap->installPixels(info, resource->pixels, info.minRowBytes());
 }
 
 ResourceProvider::ScopedReadLockSoftware::ScopedReadLockSoftware(
     ResourceProvider* resource_provider,
     ResourceId resource_id)
     : resource_provider_(resource_provider), resource_id_(resource_id) {
   const Resource* resource = resource_provider->LockForRead(resource_id, false);
   ResourceProvider::PopulateSkBitmapWithResource(&sk_bitmap_, resource);
 }
 
 ResourceProvider::ScopedReadLockSoftware::~ScopedReadLockSoftware() {
   resource_provider_->UnlockForRead(resource_id_);
 }
 
 ResourceProvider::ScopedWriteLockSoftware::ScopedWriteLockSoftware(
     ResourceProvider* resource_provider,
     ResourceId resource_id)
-    : resource_provider_(resource_provider),
-      resource_(resource_provider->LockForWrite(resource_id)) {
-  ResourceProvider::PopulateSkBitmapWithResource(&sk_bitmap_, resource_);
+    : resource_provider_(resource_provider), resource_id_(resource_id) {
+  ResourceProvider::PopulateSkBitmapWithResource(
+      &sk_bitmap_, resource_provider->LockForWrite(resource_id));
   DCHECK(valid());
 }
 
 ResourceProvider::ScopedWriteLockSoftware::~ScopedWriteLockSoftware() {
   DCHECK(thread_checker_.CalledOnValidThread());
-  resource_provider_->UnlockForWrite(resource_);
+  Resource* resource = resource_provider_->GetResource(resource_id_);
+  DCHECK(resource);
+  resource->SetSynchronized();
+  resource_provider_->UnlockForWrite(resource);
 }
 
 ResourceProvider::ScopedWriteLockGpuMemoryBuffer::
     ScopedWriteLockGpuMemoryBuffer(ResourceProvider* resource_provider,
                                    ResourceId resource_id)
-    : resource_provider_(resource_provider),
-      resource_(resource_provider->LockForWrite(resource_id)) {
-  DCHECK(IsGpuResourceType(resource_->type));
-  gpu_memory_buffer_ = std::move(resource_->gpu_memory_buffer);
-  resource_->gpu_memory_buffer = nullptr;
+    : resource_provider_(resource_provider), resource_id_(resource_id) {
+  Resource* resource = resource_provider->LockForWrite(resource_id);
+  DCHECK(IsGpuResourceType(resource->type));
+  format_ = resource->format;
+  size_ = resource->size;
+  gpu_memory_buffer_ = std::move(resource->gpu_memory_buffer);
+  resource->gpu_memory_buffer = nullptr;
 }
 
 ResourceProvider::ScopedWriteLockGpuMemoryBuffer::
     ~ScopedWriteLockGpuMemoryBuffer() {
   DCHECK(thread_checker_.CalledOnValidThread());
-  resource_provider_->UnlockForWrite(resource_);
-  if (!gpu_memory_buffer_)
-    return;
-
-  DCHECK(!resource_->gpu_memory_buffer);
-  resource_provider_->LazyCreate(resource_);
-  resource_->gpu_memory_buffer = std::move(gpu_memory_buffer_);
-  if (resource_->gpu_memory_buffer)
-    resource_->gpu_memory_buffer_id = resource_->gpu_memory_buffer->GetId();
-  resource_->allocated = true;
-  resource_provider_->LazyCreateImage(resource_);
-  resource_->dirty_image = true;
-  resource_->is_overlay_candidate = true;
-  resource_->SetSynchronized();
-
-  // GpuMemoryBuffer provides direct access to the memory used by the GPU.
-  // Read lock fences are required to ensure that we're not trying to map a
-  // buffer that is currently in-use by the GPU.
-  resource_->read_lock_fences_enabled = true;
+  Resource* resource = resource_provider_->GetResource(resource_id_);
+  DCHECK(resource);
+  if (gpu_memory_buffer_) {
+    DCHECK(!resource->gpu_memory_buffer);
+    resource_provider_->LazyCreate(resource);
+    resource->gpu_memory_buffer = std::move(gpu_memory_buffer_);
+    if (resource->gpu_memory_buffer)
+      resource->gpu_memory_buffer_id = resource->gpu_memory_buffer->GetId();
+    resource->allocated = true;
+    resource_provider_->LazyCreateImage(resource);
+    resource->dirty_image = true;
+    resource->is_overlay_candidate = true;
+    // GpuMemoryBuffer provides direct access to the memory used by the GPU.
+    // Read lock fences are required to ensure that we're not trying to map a
+    // buffer that is currently in-use by the GPU.
+    resource->read_lock_fences_enabled = true;
+  }
+  resource->SetSynchronized();
+  resource_provider_->UnlockForWrite(resource);
 }
 
 gfx::GpuMemoryBuffer*
 ResourceProvider::ScopedWriteLockGpuMemoryBuffer::GetGpuMemoryBuffer() {
   if (!gpu_memory_buffer_) {
     gpu_memory_buffer_ =
         resource_provider_->gpu_memory_buffer_manager_->AllocateGpuMemoryBuffer(
-            resource_->size, BufferFormat(resource_->format),
+            size_, BufferFormat(format_),
             gfx::BufferUsage::GPU_READ_CPU_READ_WRITE, gpu::kNullSurfaceHandle);
   }
   return gpu_memory_buffer_.get();
 }
 
 ResourceProvider::ScopedReadLockGpuMemoryBuffer::ScopedReadLockGpuMemoryBuffer(
     ResourceProvider* resource_provider,
     ResourceId resource_id)
-    : resource_provider_(resource_provider),
-      resource_id_(resource_id),
-      resource_(resource_provider->LockForRead(resource_id, true)) {}
+    : resource_provider_(resource_provider), resource_id_(resource_id) {
+  const Resource* resource = resource_provider->LockForRead(resource_id, true);
+  gpu_memory_buffer_ = resource->gpu_memory_buffer.get();
+  texture_id_ = resource->gl_id;
+}
 
 ResourceProvider::ScopedReadLockGpuMemoryBuffer::
     ~ScopedReadLockGpuMemoryBuffer() {
   DCHECK(thread_checker_.CalledOnValidThread());
   resource_provider_->UnlockForRead(resource_id_);
 }
 
-gfx::GpuMemoryBuffer*
-ResourceProvider::ScopedReadLockGpuMemoryBuffer::GetGpuMemoryBuffer() const {
-  return resource_->gpu_memory_buffer.get();
-}
-
-unsigned ResourceProvider::ScopedReadLockGpuMemoryBuffer::GetTextureId() const {
-  return resource_->gl_id;
-}
-
-ResourceId ResourceProvider::ScopedReadLockGpuMemoryBuffer::GetResourceId()
-    const {
-  return resource_id_;
-}
-
-ResourceProvider::ScopedWriteLockGr::ScopedWriteLockGr(
-    ResourceProvider* resource_provider,
-    ResourceId resource_id)
-    : resource_provider_(resource_provider),
-      resource_(resource_provider->LockForWrite(resource_id)),
-      set_sync_token_(false) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  resource_provider_->LazyAllocate(resource_);
-  if (resource_->image_id && resource_->dirty_image)
-    resource_provider_->BindImageForSampling(resource_);
-}
-
-ResourceProvider::ScopedWriteLockGr::~ScopedWriteLockGr() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK(resource_->locked_for_write);
-  if (set_sync_token_)
-    resource_->UpdateSyncToken(sync_token_);
-
-  resource_provider_->UnlockForWrite(resource_);
-}
-
-void ResourceProvider::ScopedWriteLockGr::InitSkSurface(
-    GrContext* gr_context,
-    bool use_distance_field_text,
-    bool can_use_lcd_text,
-    int msaa_sample_count) {
-  DCHECK(resource_->locked_for_write);
-
-  GrGLTextureInfo texture_info;
-  texture_info.fID = resource_->gl_id;
-  texture_info.fTarget = resource_->target;
-  GrBackendTextureDesc desc;
-  desc.fFlags = kRenderTarget_GrBackendTextureFlag;
-  desc.fWidth = resource_->size.width();
-  desc.fHeight = resource_->size.height();
-  desc.fConfig = ToGrPixelConfig(resource_->format);
-  desc.fOrigin = kTopLeft_GrSurfaceOrigin;
-  desc.fTextureHandle = skia::GrGLTextureInfoToGrBackendObject(texture_info);
-  desc.fSampleCnt = msaa_sample_count;
-
-  uint32_t flags =
-      use_distance_field_text ? SkSurfaceProps::kUseDistanceFieldFonts_Flag : 0;
-  // Use unknown pixel geometry to disable LCD text.
-  SkSurfaceProps surface_props(flags, kUnknown_SkPixelGeometry);
-  if (can_use_lcd_text) {
-    // LegacyFontHost will get LCD text and skia figures out what type to use.
-    surface_props =
-        SkSurfaceProps(flags, SkSurfaceProps::kLegacyFontHost_InitType);
-  }
-  sk_surface_ = SkSurface::MakeFromBackendTextureAsRenderTarget(
-      gr_context, desc, &surface_props);
-}
-
-void ResourceProvider::ScopedWriteLockGr::ReleaseSkSurface() {
-  DCHECK(sk_surface_);
-  sk_surface_->prepareForExternalIO();
-  sk_surface_.reset();
-}
-
 ResourceProvider::SynchronousFence::SynchronousFence(
     gpu::gles2::GLES2Interface* gl)
     : gl_(gl), has_synchronized_(true) {
 }
 
 ResourceProvider::SynchronousFence::~SynchronousFence() {
 }
 
 void ResourceProvider::SynchronousFence::Set() {
   has_synchronized_ = false;
@@ skipping 536 matching lines @@
   if (resource->type == RESOURCE_TYPE_GPU_MEMORY_BUFFER) {
     resource->gpu_memory_buffer =
         gpu_memory_buffer_manager_->AllocateGpuMemoryBuffer(
             size, BufferFormat(format),
             gfx::BufferUsage::GPU_READ_CPU_READ_WRITE, gpu::kNullSurfaceHandle);
     if (resource->gpu_memory_buffer)
       resource->gpu_memory_buffer_id = resource->gpu_memory_buffer->GetId();
     LazyCreateImage(resource);
     resource->dirty_image = true;
     resource->is_overlay_candidate = true;
+    // GpuMemoryBuffer provides direct access to the memory used by the GPU.
+    // Read lock fences are required to ensure that we're not trying to map a
+    // buffer that is currently in-use by the GPU.
+    resource->read_lock_fences_enabled = true;
   } else if (use_texture_storage_ext_ &&
              IsFormatSupportedForStorage(format, use_texture_format_bgra_) &&
              (resource->hint & TEXTURE_HINT_IMMUTABLE)) {
     GLenum storage_format = TextureToStorageFormat(format);
     gl->TexStorage2DEXT(resource->target, 1, storage_format, size.width(),
                         size.height());
   } else {
     // ETC1 does not support preallocation.
     if (format != ETC1) {
       gl->TexImage2D(resource->target, 0, GLInternalFormat(format),
@@ skipping 156 matching lines @@
 
     const int kImportance = 2;
     pmd->CreateSharedGlobalAllocatorDump(guid);
     pmd->AddOwnershipEdge(dump->guid(), guid, kImportance);
   }
 
   return true;
 }
 
 }  // namespace cc