Move CrossThreadHolder to CrossThreadHolder.h

Source/modules/fetch/CrossThreadHolder.h

+// Copyright 2015 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 CrossThreadHolder_h
+#define CrossThreadHolder_h
+
+#include "core/dom/ActiveDOMObject.h"
+#include "core/dom/CrossThreadTask.h"
+#include "core/dom/ExecutionContext.h"
+#include "public/platform/WebTraceLocation.h"
+#include "wtf/Locker.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefPtr.h"
+#include "wtf/ThreadingPrimitives.h"
+
+namespace blink {
+
+// CrossThreadHolder<T> provides cross-thread access to |obj| of class T
+// bound to the thread of |executionContext| where |obj| is created.
+// - CrossThreadHolder<T> can be passed across threads.
+// - |obj|'s methods are called on the thread of |executionContext|
+//   via CrossThreadHolder<T>::postTask().
+// - |obj| is destructed on the thread of |executionContext|
+//   when |executionContext| is stopped or
+//   CrossThreadHolder is destructed (earlier of them).
+//   Note: |obj|'s destruction can be slightly after CrossThreadHolder.
+template<typename T>
+class CrossThreadHolder final {
+public:
+    // Must be called on the thread where |obj| is created
+    // (== the thread of |executionContext|).
+    // The current thread must be attached to Oilpan.
+    static PassOwnPtr<CrossThreadHolder<T>> create(ExecutionContext* executionContext, PassOwnPtr<T> obj)
+    {
+        ASSERT(executionContext->isContextThread());
+        return adoptPtr(new CrossThreadHolder(executionContext, obj));
+    }
+
+    // Can be called from any thread.
+    // Executes |task| with |obj| and |executionContext| on the thread of
+    // |executionContext|.
+    // NOTE: |task| might be silently ignored (i.e. not executed) and
+    // destructed (possibly on the calling thread or on the thread of
+    // |executionContext|) when |executionContext| is stopped or
+    // CrossThreadHolder is destructed.
+    void postTask(PassOwnPtr<WTF::Function<void(T*, ExecutionContext*)>> task)
+    {
+        MutexLocker locker(m_mutex->mutex());
+        if (!m_bridge) {
+            // The bridge has already disappeared.
+            return;
+        }
+        m_bridge->executionContext()->postTask(FROM_HERE, createCrossThreadTask(&Bridge::runTask, m_bridge.get(), task));
+    }
+
+    ~CrossThreadHolder()
+    {
+        MutexLocker locker(m_mutex->mutex());
+        clearInternal();
+    }
+
+private:
+    // Object graph:
+    //                 +------+                          +-----------------+
+    //     T <-OwnPtr- |Bridge| ---------RawPtr--------> |CrossThreadHolder|
+    //                 |      | <-CrossThreadPersistent- |                 |
+    //                 +------+                          +-----------------+
+    //                    |                                    |
+    //                    +--RefPtr--> MutexWrapper <--RefPtr--+
+    // The CrossThreadPersistent/RawPtr between CrossThreadHolder and Bridge
+    // are protected by MutexWrapper
+    // and cleared when CrossThreadHolder::clearInternal() is called, i.e.:
+    // [1] when |executionContext| is stopped, or
+    // [2] when CrossThreadHolder is destructed.
+    // Then Bridge is shortly garbage collected and T is destructed.
+
+    class MutexWrapper : public ThreadSafeRefCounted<MutexWrapper> {
+    public:
+        static PassRefPtr<MutexWrapper> create() { return adoptRef(new MutexWrapper()); }
+        Mutex& mutex() { return m_mutex; }
+    private:
+        MutexWrapper() = default;
+        Mutex m_mutex;
+    };
+
+    // All methods except for clearInternal()
+    // must be called on |executionContext|'s thread.
+    class Bridge
+        : public GarbageCollectedFinalized<Bridge>
+        , public ActiveDOMObject {
+        WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(Bridge);
+    public:
+        Bridge(ExecutionContext* executionContext, PassOwnPtr<T> obj, PassRefPtr<MutexWrapper> mutex, CrossThreadHolder* holder)
+            : ActiveDOMObject(executionContext)
+            , m_obj(obj)
+            , m_mutex(mutex)
+            , m_holder(holder)
+        {
+            suspendIfNeeded();
+        }
+
+        DEFINE_INLINE_TRACE()
+        {
+            ActiveDOMObject::trace(visitor);
+        }
+
+        T* getObject() const { return m_obj.get(); }
+
+        // Must be protected by |m_mutex|.
+        // Is called from CrossThreadHolder::clearInternal() and
+        // can be called on any thread.
+        void clearInternal()
+        {
+            // We don't clear |m_obj| here to destruct |m_obj| on the thread
+            // of |executionContext|.
+            m_holder = nullptr;
+        }
+
+        void runTask(PassOwnPtr<WTF::Function<void(T*, ExecutionContext*)>> task)
+        {
+            ASSERT(executionContext()->isContextThread());
+            if (m_obj)
+                (*task)(m_obj.get(), executionContext());
+        }
+
+    private:
+        // ActiveDOMObject
+        void stop() override
+        {
+            ASSERT(executionContext()->isContextThread());
+            {
+                MutexLocker locker(m_mutex->mutex());
+                if (m_holder)
+                    m_holder->clearInternal();
+                ASSERT(!m_holder);
+            }
+
+            // We have to destruct |*m_obj| here because destructing |*m_obj|
+            // in ~Bridge() might be too late when |executionContext| is
+            // stopped.
+            m_obj.clear();
+        }
+
+
+        OwnPtr<T> m_obj;
+        // All accesses to |m_holder| must be protected by |m_mutex|.
+        RefPtr<MutexWrapper> m_mutex;
+        CrossThreadHolder* m_holder;
+    };
+
+    // Must be protected by |m_mutex|.
+    void clearInternal()
+    {
+        if (m_bridge)
+            m_bridge->clearInternal();
+        m_bridge.clear();
+    }
+
+    CrossThreadHolder(ExecutionContext* executionContext, PassOwnPtr<T> obj)
+        : m_mutex(MutexWrapper::create())
+        , m_bridge(new Bridge(executionContext, obj, m_mutex, this))
+    {
+    }
+
+    RefPtr<MutexWrapper> m_mutex;
+    // |m_bridge| is protected by |m_mutex|.
+    // |m_bridge| is cleared before the thread that allocated |*m_bridge|
+    // is stopped.
+    CrossThreadPersistent<Bridge> m_bridge;
+};
+
+} // namespace blink
+
+#endif // CrossThreadHolder_h