Introduce DataConsumerHandleTee

Source/modules/fetch/DataConsumerTeeTest.cpp

+// 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.
+
+#include "config.h"
+#include "modules/fetch/DataConsumerTee.h"
+
+#include "core/testing/DummyPageHolder.h"
+#include "core/testing/NullExecutionContext.h"
+#include "platform/Task.h"
+#include "platform/ThreadSafeFunctional.h"
+#include "platform/WebThreadSupportingGC.h"
+#include "public/platform/Platform.h"
+#include "public/platform/WebThread.h"
+#include "public/platform/WebTraceLocation.h"
+#include "public/platform/WebWaitableEvent.h"
+#include "wtf/Deque.h"
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefPtr.h"
+#include "wtf/ThreadSafeRefCounted.h"
+#include "wtf/ThreadingPrimitives.h"
+#include "wtf/Vector.h"
+
+#include <gtest/gtest.h>
+#include <string.h>
+#include <v8.h>
+
+namespace blink {
+namespace {
+
+using Result = WebDataConsumerHandle::Result;
+const WebDataConsumerHandle::Flags kNone = WebDataConsumerHandle::FlagNone;
+const Result kOk = WebDataConsumerHandle::Ok;
+const Result kShouldWait = WebDataConsumerHandle::ShouldWait;
+const Result kDone = WebDataConsumerHandle::Done;
+const Result kUnexpectedError = WebDataConsumerHandle::UnexpectedError;
+
+class Command final {
+public:
+    enum Name {
+        Data,
+        Done,
+        Error,
+        Wait,
+    };
+
+    Command(Name name) : m_name(name) { }
+    Command(Name name, const Vector<char>& body) : m_name(name), m_body(body) { }
+    Command(Name name, const char* body, size_t size) : m_name(name)
+    {
+        m_body.append(body, size);
+    }
+    Command(Name name, const char* body) : Command(name, body, strlen(body)) { }
+    Name name() const { return m_name; }
+    const Vector<char>& body() const { return m_body; }
+
+private:
+    const Name m_name;
+    Vector<char> m_body;
+};
+
+class Handle final : public WebDataConsumerHandle {

[hiroshige, 2015/06/23 09:20:44]

Please add a comment that says Handle is a WebDataConsumerHandle constructed
from a sequence of Command by Handle:add().

[yhirano, 2015/06/23 10:18:19]

Done.

+public:
+    class Context final : public ThreadSafeRefCounted<Context> {
+    public:
+        static PassRefPtr<Context> create() { return adoptRef(new Context); }
+
+        // This function cannot be called after creating a tee.
+        void add(const Command& command)
+        {
+            m_commands.append(command);
+        }
+
+        void notify()
+        {
+            if (!m_client)
+                return;
+            ASSERT(m_readerThread);
+            m_readerThread->postTask(FROM_HERE, new Task(threadSafeBind(&Context::notifyInternal, this)));
+        }
+
+        void attachReader(WebDataConsumerHandle::Client* client)
+        {
+            ASSERT(!m_readerThread);
+            ASSERT(!m_client);
+            m_readerThread = Platform::current()->currentThread();
+            m_client = client;
+
+            if (m_client && !(isEmpty() && m_result == kShouldWait))
+                notify();
+        }
+        void detachReader()
+        {
+            ASSERT(m_readerThread && m_readerThread->isCurrentThread());
+            m_readerThread = nullptr;
+            m_client = nullptr;
+            if (!m_isHandleAttached)
+                m_detachEvent->signal();

[hiroshige, 2015/06/23 09:20:44]

Can we move |m_detachEvent->signal()| to the dtor and remove
|m_isHandleAttached|? (I think Context is destructed shortly after
detachReader() if |!m_isHandleAttached|, because the reader with the last 
reference to |this| is destructed).

[yhirano, 2015/06/23 10:18:20]

That assumption does not hold in DetachBothDestinationsShouldStopSourceReader.

+        }
+
+        void detachHandle()
+        {
+            m_isHandleAttached = false;
+            if (!m_readerThread)
+                m_detachEvent->signal();

[hiroshige, 2015/06/23 09:20:44]

ditto, and can we remove detachHandle()?

[yhirano, 2015/06/23 10:18:19]

Ditto

+        }
+
+        bool isEmpty() const { return m_commands.isEmpty(); }
+        const Command& top()
+        {
+            ASSERT(!isEmpty());
+            return m_commands.first();
+        }
+
+        void consume(size_t size)
+        {
+            ASSERT(!isEmpty());
+            ASSERT(size + m_offset <= top().body().size());
+            bool fullyConsumed = (size + m_offset == top().body().size());

[hiroshige, 2015/06/23 09:20:45]

">=" instead of "==" is a little more robust and consistent.

[yhirano, 2015/06/23 10:18:20]

Done.

+            if (fullyConsumed) {
+                m_offset = 0;
+                m_commands.removeFirst();
+            } else {
+                m_offset += size;
+            }
+        }
+
+        size_t offset() const { return m_offset; }
+        Result result() const { return m_result; }
+        void setDone() { m_result = Done; }
+        void setError() { m_result = UnexpectedError; }
+
+        Mutex& mutex()
+        {
+            return m_mutex;
+        }
+
+        WebWaitableEvent* detachEvent() { return m_detachEvent.get(); }

[hiroshige, 2015/06/23 09:20:45]

nit optional: detachEvent() seems "to detach an event".

[yhirano, 2015/06/23 10:18:19]

Done.

+
+    private:
+        Context()
+            : m_offset(0)
+            , m_readerThread(nullptr)
+            , m_client(nullptr)
+            , m_result(ShouldWait)
+            , m_isHandleAttached(true)
+            , m_detachEvent(adoptPtr(Platform::current()->createWaitableEvent()))
+        {
+        }
+
+        void notifyInternal()
+        {
+            {
+                MutexLocker locker(m_mutex);
+                if (!m_client || !m_readerThread->isCurrentThread()) {
+                    // There is no client, or a new reader is attached.
+                    return;
+                }
+            }
+            // The reading thread is the current thread.
+            m_client->didGetReadable();
+        }
+
+        Deque<Command> m_commands;
+        size_t m_offset;
+        WebThread* m_readerThread;
+        Client* m_client;
+        Result m_result;
+        bool m_isHandleAttached;
+        Mutex m_mutex;
+        OwnPtr<WebWaitableEvent> m_detachEvent;
+    };
+
+    class ReaderImpl final : public Reader {
+    public:
+        ReaderImpl(PassRefPtr<Context> context, Client* client)
+            : m_context(context)
+        {
+            MutexLocker locker(m_context->mutex());

[hiroshige, 2015/06/23 09:20:44]

I prefer taking lock in Context, because it is clearer for me who takes locks.

[yhirano, 2015/06/23 10:18:19]

Done.

+            m_context->attachReader(client);
+        }
+        ~ReaderImpl()
+        {
+            MutexLocker locker(m_context->mutex());

[hiroshige, 2015/06/23 09:20:44]

ditto.

[yhirano, 2015/06/23 10:18:19]

Done.

+            m_context->detachReader();
+        }
+
+        Result read(void* buffer, size_t size, Flags flags, size_t* readSize) override
+        {
+            const void* src = nullptr;
+            Result result = beginRead(&src, flags, readSize);
+            if (result != Ok)
+                return result;
+            memcpy(buffer, src, *readSize);

[hiroshige, 2015/06/23 09:20:44]

We should take min(size, *readSize).

[yhirano, 2015/06/23 10:18:20]

Done.

+            return endRead(*readSize);
+        }
+        Result beginRead(const void** buffer, Flags, size_t* available) override
+        {
+            MutexLocker locker(m_context->mutex());

[hiroshige, 2015/06/23 09:20:44]

ditto, and can we move this implementation to Context and let
ReaderImpl::beginRead() to call it?

[yhirano, 2015/06/23 10:18:19]

Done.

+            *buffer = nullptr;
+            *available = 0;
+            if (m_context->isEmpty())
+                return m_context->result();
+
+            const Command& command = m_context->top();
+            Result result = Ok;
+            switch (command.name()) {
+            case Command::Data: {
+                auto& body = command.body();
+                *available = body.size() - m_context->offset();
+                *buffer = body.data() + m_context->offset();
+                result = Ok;
+                break;
+            }
+            case Command::Done:
+                m_context->setDone();
+                m_context->consume(0);
+                result = Done;
+                break;
+            case Command::Wait:
+                m_context->consume(0);
+                result = ShouldWait;
+                m_context->notify();
+                break;
+            case Command::Error:
+                m_context->setError();
+                m_context->consume(0);
+                result = UnexpectedError;
+                break;
+            }
+            return result;
+        }
+        Result endRead(size_t readSize) override
+        {
+            m_context->consume(readSize);
+            return Ok;
+        }
+
+    private:
+        RefPtr<Context> m_context;
+    };
+
+    Handle() : m_context(Context::create()) { }
+    ~Handle()
+    {
+        MutexLocker locker(m_context->mutex());
+        m_context->detachHandle();
+    }
+
+    ReaderImpl* obtainReaderInternal(Client* client) override { return new ReaderImpl(m_context, client); }
+
+    // Add a command to this handle. This function must be called on the
+    // creator thread. This function must be called BEFORE any reader is
+    // obtained.
+    void add(const Command& command)
+    {
+        MutexLocker locker(m_context->mutex());
+        m_context->add(command);
+    }
+
+    Context* context() { return m_context.get(); };
+
+private:
+    RefPtr<Context> m_context;
+};
+
+class TestingThread final {
+public:
+    explicit TestingThread(const char* name)
+        : m_thread(WebThreadSupportingGC::create(name))
+        , m_waitableEvent(adoptPtr(Platform::current()->createWaitableEvent()))
+        , m_isolate(nullptr)
+    {
+        m_thread->postTask(FROM_HERE, new Task(threadSafeBind(&TestingThread::initialize, AllowCrossThreadAccess(this))));
+        m_waitableEvent->wait();
+    }
+
+    ~TestingThread()
+    {
+        m_thread->postTask(FROM_HERE, new Task(threadSafeBind(&TestingThread::shutdown, AllowCrossThreadAccess(this))));
+        m_waitableEvent->wait();
+    }
+
+    WebThreadSupportingGC* thread() { return m_thread.get(); }
+    ExecutionContext* executionContext() { return m_executionContext.get(); }
+
+private:
+    void initialize()
+    {
+        m_isolate = v8::Isolate::New(v8::Isolate::CreateParams());
+        m_isolate->Enter();
+        m_thread->initialize();
+        m_executionContext = adoptRefWillBeNoop(new NullExecutionContext());
+        m_waitableEvent->signal();
+    }
+
+    void shutdown()
+    {
+        m_executionContext = nullptr;
+        m_thread->shutdown();
+        m_isolate->Exit();
+        m_isolate->Dispose();
+        m_isolate = nullptr;
+        m_waitableEvent->signal();
+    }
+
+    OwnPtr<WebThreadSupportingGC> m_thread;
+    OwnPtr<WebWaitableEvent> m_waitableEvent;
+    RefPtrWillBePersistent<NullExecutionContext> m_executionContext;
+    v8::Isolate* m_isolate;
+};
+
+class HandleReader : public WebDataConsumerHandle::Client {
+public:
+    HandleReader() : m_finalResult(kOk) { }
+
+    // Need to wait for the event signal after this function is called.
+    void start(PassOwnPtr<WebDataConsumerHandle> handle)
+    {
+        m_thread = adoptPtr(new TestingThread("reading thread"));
+        m_thread->thread()->postTask(FROM_HERE, new Task(threadSafeBind(&HandleReader::obtainReader, AllowCrossThreadAccess(this), handle)));
+        m_waitableEvent = adoptPtr(Platform::current()->createWaitableEvent());

[hiroshige, 2015/06/23 09:20:44]

L322 sould be before L321, because didGetReadable() can be executed between L321
and L322?

[yhirano, 2015/06/23 10:18:19]

Done.

+    }
+
+    void didGetReadable() override
+    {
+        Result r = kOk;
+        char buffer[3];
+        while (true) {
+            size_t size;
+            r = m_reader->read(buffer, sizeof(buffer), kNone, &size);
+            if (r == kShouldWait)
+                return;
+            if (r != kOk)
+                break;
+            m_readString.append(String(buffer, size));
+        }
+        m_finalResult = r;
+        m_reader = nullptr;
+        m_waitableEvent->signal();
+    }
+
+    WebWaitableEvent* waitableEvent() { return m_waitableEvent.get(); }
+
+    // These should be accessed after the thread joines.

[hiroshige, 2015/06/23 09:20:44]

nit: s/joines/joins/?

[yhirano, 2015/06/23 10:18:20]

Done.

+    const String& readString() const { return m_readString; }
+    Result finalResult() const { return m_finalResult; }
+
+private:
+    void obtainReader(PassOwnPtr<WebDataConsumerHandle> handle)
+    {
+        m_reader = handle->obtainReader(this);
+    }
+
+    OwnPtr<TestingThread> m_thread;
+    OwnPtr<WebDataConsumerHandle::Reader> m_reader;
+    String m_readString;
+    Result m_finalResult;
+    OwnPtr<WebWaitableEvent> m_waitableEvent;
+};
+
+class HandleTwoPhaseReader : public WebDataConsumerHandle::Client {
+public:
+    HandleTwoPhaseReader() : m_finalResult(kOk) { }
+
+    // Need to wait for the event signal after this function is called.
+    void start(PassOwnPtr<WebDataConsumerHandle> handle)
+    {
+        m_thread = adoptPtr(new TestingThread("reading thread"));
+        m_thread->thread()->postTask(FROM_HERE, new Task(threadSafeBind(&HandleTwoPhaseReader::obtainReader, AllowCrossThreadAccess(this), handle)));
+        m_waitableEvent = adoptPtr(Platform::current()->createWaitableEvent());

[hiroshige, 2015/06/23 09:20:44]

ditto.

[yhirano, 2015/06/23 10:18:19]

Done.

+    }
+
+    void didGetReadable() override
+    {
+        Result r = kOk;
+        while (true) {
+            const void* buffer = nullptr;
+            size_t size;
+            r = m_reader->beginRead(&buffer, kNone, &size);
+            if (r == kShouldWait)
+                return;
+            if (r != kOk)
+                break;
+            // Read smaller than availabe in order to test |endRead|.
+            size_t readSize = std::max(size * 2 / 3, static_cast<size_t>(1));

[hiroshige, 2015/06/23 09:20:45]

BTW, can we assume beginRead()'s size > 0?

[yhirano, 2015/06/23 10:18:20]

No I think, calling read or beginRead with zero size may be useful to detect
errors, although I didn't specified the behavior yet.

+            m_readString.append(String(static_cast<const char*>(buffer), readSize));
+            m_reader->endRead(readSize);
+        }
+        m_finalResult = r;
+        m_reader = nullptr;
+        m_waitableEvent->signal();
+    }
+
+    WebWaitableEvent* waitableEvent() { return m_waitableEvent.get(); }
+
+    // These should be accessed after the thread joines.

[hiroshige, 2015/06/23 09:20:45]

nit: joins.

[yhirano, 2015/06/23 10:18:19]

Done.

+    const String& readString() const { return m_readString; }
+    Result finalResult() const { return m_finalResult; }
+
+private:
+    void obtainReader(PassOwnPtr<WebDataConsumerHandle> handle)
+    {
+        m_reader = handle->obtainReader(this);
+    }
+
+    OwnPtr<TestingThread> m_thread;
+    OwnPtr<WebDataConsumerHandle::Reader> m_reader;
+    String m_readString;
+    Result m_finalResult;
+    OwnPtr<WebWaitableEvent> m_waitableEvent;
+};
+
+class TeeCreationThread {
+public:
+    void run(PassOwnPtr<WebDataConsumerHandle> src, OwnPtr<WebDataConsumerHandle>* dest1, OwnPtr<WebDataConsumerHandle>* dest2)
+    {
+        m_thread = adoptPtr(new TestingThread("src thread"));
+        m_waitableEvent = adoptPtr(Platform::current()->createWaitableEvent());
+        m_thread->thread()->postTask(FROM_HERE, new Task(threadSafeBind(&TeeCreationThread::runInternal, AllowCrossThreadAccess(this), src, AllowCrossThreadAccess(dest1), AllowCrossThreadAccess(dest2))));
+        m_waitableEvent->wait();
+    }
+
+    TestingThread* thread() { return m_thread.get(); }
+
+private:
+    void runInternal(PassOwnPtr<WebDataConsumerHandle> src, OwnPtr<WebDataConsumerHandle>* dest1, OwnPtr<WebDataConsumerHandle>* dest2)
+    {
+        DataConsumerTee::create(m_thread->executionContext(), src, dest1, dest2);
+        m_waitableEvent->signal();
+    }
+
+    OwnPtr<TestingThread> m_thread;
+    OwnPtr<WebWaitableEvent> m_waitableEvent;
+};
+
+TEST(DataConsumerTeeTest, CreateDone)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Done));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleReader r1, r2;
+    r1.start(dest1.release());
+    r2.start(dest2.release());
+
+    r1.waitableEvent()->wait();
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r1.finalResult());
+    EXPECT_EQ(String(), r1.readString());
+
+    EXPECT_EQ(kDone, r2.finalResult());
+    EXPECT_EQ(String(), r2.readString());
+}
+
+TEST(DataConsumerTeeTest, Read)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Data, "world"));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Done));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleReader r1, r2;
+    r1.start(dest1.release());
+    r2.start(dest2.release());
+
+    r1.waitableEvent()->wait();
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r1.finalResult());
+    EXPECT_EQ("hello, world", r1.readString());
+
+    EXPECT_EQ(kDone, r2.finalResult());
+    EXPECT_EQ("hello, world", r2.readString());
+}
+
+TEST(DataConsumerTeeTest, TwoPhaseRead)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Data, "world"));
+    src->add(Command(Command::Wait));
+    src->add(Command(Command::Done));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleTwoPhaseReader r1, r2;
+    r1.start(dest1.release());
+    r2.start(dest2.release());
+
+    r1.waitableEvent()->wait();
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r1.finalResult());
+    EXPECT_EQ("hello, world", r1.readString());
+
+    EXPECT_EQ(kDone, r2.finalResult());
+    EXPECT_EQ("hello, world", r2.readString());
+}
+
+TEST(DataConsumerTeeTest, Error)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Data, "world"));
+    src->add(Command(Command::Error));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleReader r1, r2;
+    r1.start(dest1.release());
+    r2.start(dest2.release());
+
+    r1.waitableEvent()->wait();
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kUnexpectedError, r1.finalResult());
+    EXPECT_EQ(kUnexpectedError, r2.finalResult());
+}
+
+TEST(DataConsumerTeeTest, DetachSource)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Data, "world"));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleReader r1, r2;
+    r1.start(dest1.release());
+    r2.start(dest2.release());
+
+    t = nullptr;
+
+    r1.waitableEvent()->wait();
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kUnexpectedError, r1.finalResult());
+    EXPECT_EQ(kUnexpectedError, r2.finalResult());
+}
+
+TEST(DataConsumerTeeTest, DetachSourceAfterReadingDone)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Data, "world"));
+    src->add(Command(Command::Done));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    HandleReader r1, r2;
+    r1.start(dest1.release());
+    r1.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r1.finalResult());
+    EXPECT_EQ("hello, world", r1.readString());
+
+    t = nullptr;
+
+    r2.start(dest2.release());
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r2.finalResult());
+    EXPECT_EQ("hello, world", r2.readString());
+}
+
+TEST(DataConsumerTeeTest, DetachOneDestination)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Data, "world"));
+    src->add(Command(Command::Done));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    dest1 = nullptr;
+
+    HandleReader r2;
+    r2.start(dest2.release());
+    r2.waitableEvent()->wait();
+
+    EXPECT_EQ(kDone, r2.finalResult());
+    EXPECT_EQ("hello, world", r2.readString());
+}
+
+TEST(DataConsumerTeeTest, DetachBothDestinationsShouldStopSourceReader)
+{
+    OwnPtr<Handle> src(adoptPtr(new Handle));
+    RefPtr<Handle::Context> context(src->context());
+    OwnPtr<WebDataConsumerHandle> dest1, dest2;
+
+    src->add(Command(Command::Data, "hello, "));
+    src->add(Command(Command::Data, "world"));
+
+    OwnPtr<TeeCreationThread> t = adoptPtr(new TeeCreationThread());
+    t->run(src.release(), &dest1, &dest2);
+
+    ASSERT_TRUE(dest1);
+    ASSERT_TRUE(dest2);
+
+    dest1 = nullptr;
+    dest2 = nullptr;
+
+    // Collect garbage to finalize the source reader.
+    Heap::collectGarbage(ThreadState::HeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
+    context->detachEvent()->wait();
+}
+
+} // namespace
+} // namespace blink