Allow canvases to be GPU-accelerated in Workers

third_party/WebKit/Source/platform/graphics/gpu/SharedGpuContext.cpp

+// Copyright 2016 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 "platform/graphics/gpu/SharedGpuContext.h"
+
+#include "gpu/command_buffer/client/gles2_interface.h"
+#include "platform/CrossThreadFunctional.h"
+#include "platform/WaitableEvent.h"
+#include "public/platform/Platform.h"
+#include "public/platform/WebGraphicsContext3DProvider.h"
+#include "public/platform/WebTaskRunner.h"
+
+namespace blink {
+
+SharedGpuContext* SharedGpuContext::getInstanceForCurrentThread()
+{
+    DEFINE_THREAD_SAFE_STATIC_LOCAL(ThreadSpecific<SharedGpuContext>, threadSpecificInstance, new ThreadSpecific<SharedGpuContext>);

[Stephen White, 2016/09/01 15:43:54]

As discussed, it might be nice to move this into some other per-worker owned
object, rather than using a TLS singleton. Also, please add a test for two
OffscreenCanvases in two separate workers, if that doesn't already exist.

[haraken, 2016/09/01 17:33:05]

Yeah, agreed. We want to avoid this kind of thread-local storage usage.

+    return threadSpecificInstance;
+}
+
+SharedGpuContext::SharedGpuContext()
+    : m_contextId(kNoSharedContext)
+{
+    createContextProvider();
+}
+
+void SharedGpuContext::createContextProviderOnMainThread(WaitableEvent* waitableEvent)
+{
+    DCHECK(isMainThread());
+    Platform::ContextAttributes contextAttributes;
+    contextAttributes.webGLVersion = 1; // GLES2
+    Platform::GraphicsInfo graphicsInfo;
+    m_contextProvider = wrapUnique(Platform::current()->createOffscreenGraphicsContext3DProvider(
+        contextAttributes, WebURL(), nullptr, &graphicsInfo));
+    if (waitableEvent)
+        waitableEvent->signal();
+}
+
+void SharedGpuContext::createContextProvider()
+{
+    std::unique_ptr<WebGraphicsContext3DProvider> oldContextProvider = std::move(m_contextProvider);
+    if (isMainThread()) {
+        m_contextProvider = wrapUnique(blink::Platform::current()->createSharedOffscreenGraphicsContext3DProvider());
+    } else {
+        // This synchronous round-trip to the main thread is the reason why SharedGpuContext
+        // encasulates the context provider: so we only have to do this once per thread.
+        WaitableEvent waitableEvent;
+        WebTaskRunner* taskRunner = Platform::current()->mainThread()->getWebTaskRunner();
+            taskRunner->postTask(BLINK_FROM_HERE, crossThreadBind(&SharedGpuContext::createContextProviderOnMainThread, crossThreadUnretained(this), crossThreadUnretained(&waitableEvent)));
+        waitableEvent.wait();
+        if (m_contextProvider && !m_contextProvider->bindToCurrentThread())
+            m_contextProvider = nullptr;
+    }
+
+    if (m_contextProvider) {
+        m_contextId++;
+        // In the unlikely event of an overflow...
+        if (m_contextId == kNoSharedContext)
+            m_contextId++;
+    } else {
+        m_contextProvider = std::move(oldContextProvider);
+    }
+}
+
+unsigned SharedGpuContext::contextId()
+{
+    SharedGpuContext* thisPtr = getInstanceForCurrentThread();
+    return thisPtr->m_contextId;
+}
+
+gpu::gles2::GLES2Interface* SharedGpuContext::gl()
+{
+    SharedGpuContext* thisPtr = getInstanceForCurrentThread();
+    if (thisPtr->m_contextProvider)
+        return thisPtr->m_contextProvider->contextGL();
+    return nullptr;
+}
+
+GrContext* SharedGpuContext::gr()
+{
+    SharedGpuContext* thisPtr = getInstanceForCurrentThread();
+    if (thisPtr->m_contextProvider)
+        return thisPtr->m_contextProvider->grContext();
+    return nullptr;
+}
+
+bool SharedGpuContext::isValid()
+{
+    SharedGpuContext* thisPtr = getInstanceForCurrentThread();
+    if (!thisPtr->m_contextProvider)
+        return false;
+    return thisPtr->m_contextProvider->contextGL()->GetGraphicsResetStatusKHR() == GL_NO_ERROR;
+}
+
+bool SharedGpuContext::restore()
+{
+    if (!isValid())
+        getInstanceForCurrentThread()->createContextProvider();
+    return isValid();
+}
+
+} // blink