Add methods for creating V8 extras-based ReadableStreams from C++

third_party/WebKit/Source/bindings/core/v8/ReadableStreamController.h

+// 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.
+
+#ifndef ReadableStreamController_h
+#define ReadableStreamController_h
+
+#include "bindings/core/v8/ScopedPersistent.h"
+#include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/ToV8.h"
+#include "bindings/core/v8/V8BindingMacros.h"
+#include "core/CoreExport.h"
+#include "platform/heap/Handle.h"
+#include <v8.h>
+
+namespace blink {
+
+class CORE_EXPORT ReadableStreamController final : public GarbageCollectedFinalized<ReadableStreamController> {
+public:
+    DEFINE_INLINE_TRACE() {}
+
+    explicit ReadableStreamController(ScriptValue stream)
+        : m_scriptState(stream.scriptState())
+        , m_stream(stream.isolate(), stream.v8Value())
+    {
+        m_stream.setWeak(&m_stream, ReadableStreamController::streamWeakCallback);
+    }
+
+    // Users of the ReadableStreamController can call this to note that the stream has been canceled and thus they
+    // don't anticipate using the ReadableStreamController anymore. (close/desiredSize/enqueue/error will become no-ops
+    // afterward.)
+    void noteHasBeenCanceled()
+    {
+        m_stream.clear();
+    }
+
+    bool isActive() const
+    {
+        return !m_stream.isEmpty();
+    }
+
+    void close()
+    {
+        if (m_stream.isEmpty())

[yhirano, 2016/01/25 11:10:32]

m_stream can become empty whenever GC runs, so I prefer the following pattern
than the current one:

v8::Local<v8::Value> stream = m_stream.newLocal(isolate);
if (stream.IsEmpty())
    return;
// Use |stream| below.

[domenic, 2016/02/02 22:59:55]

Because GC happens on another thread and can interleave within the lines of the
method? Done.

[yhirano, 2016/02/03 11:04:42]

No, v8 GC doesn't run unless we use v8 functionality. But in some cases it is
easy to overlook v8 calls, so I generally like binding to a v8::Local handle in
front.

+            return;
+
+        ScriptState::Scope scope(m_scriptState);
+        v8::Isolate* isolate = m_scriptState->isolate();
+
+        v8::Local<v8::Value> args[] = { m_stream.newLocal(isolate) };
+        v8CallExtraOrCrash(m_scriptState, "CloseReadableStream", args);

[haraken, 2016/01/25 00:13:29]

I haven't yet checked if we should add a MicroTaskSuppressionScope. If this is
an internal function (i.e., not user script), we need to add a
MicroTaskSuppressionScope.

[domenic, 2016/02/02 22:59:55]

I am not sure what you mean exactly. This is a V8 extra function, so it is kind
of in between. I only added MicrotaskSuppressionScope where not adding it caused
crashes. But maybe we should just add it to all calls into V8 extra functions?

+
+        m_stream.clear();
+    }
+
+    double desiredSize() const
+    {
+        if (m_stream.isEmpty())
+            return 0;
+
+        ScriptState::Scope scope(m_scriptState);
+        v8::Isolate* isolate = m_scriptState->isolate();
+
+        v8::Local<v8::Value> args[] = { m_stream.newLocal(isolate) };
+        v8::Local<v8::Value> result = v8CallExtraOrCrash(m_scriptState, "GetReadableStreamDesiredSize", args);
+
+        return result.As<v8::Number>()->Value();
+    }
+
+    template <typename ChunkType>
+    void enqueue(ChunkType chunk) const
+    {
+        if (m_stream.isEmpty())
+            return;
+
+        ScriptState::Scope scope(m_scriptState);
+
+        v8::Local<v8::Value> jsChunk = toV8(chunk, m_scriptState);
+        v8::Local<v8::Value> args[] = { m_stream.newLocal(m_scriptState->isolate()), jsChunk };
+        v8CallExtraOrCrash(m_scriptState, "EnqueueInReadableStream", args);
+    }
+
+    template <typename ErrorType>
+    void error(ErrorType e)
+    {
+        if (m_stream.isEmpty())
+            return;
+
+        ScriptState::Scope scope(m_scriptState);
+
+        v8::Local<v8::Value> jsError = toV8(e, m_scriptState);
+        v8::Local<v8::Value> args[] = { m_stream.newLocal(m_scriptState->isolate()), jsError };
+        v8CallExtraOrCrash(m_scriptState, "ErrorReadableStream", args);
+
+        m_stream.clear();
+    }
+
+private:
+    static void streamWeakCallback(const v8::WeakCallbackInfo<ScopedPersistent<v8::Value>>& weakInfo)
+    {
+        weakInfo.GetParameter()->clear();
+    }
+
+    ScopedPersistent<v8::Value> m_stream;
+    ScriptState* m_scriptState;

[haraken, 2016/01/25 00:13:29]

This should be RefPtr<ScriptState>. Otherwise it can go stale.

[domenic, 2016/02/02 22:59:55]

Done. This makes the code more awkward in a number of places... why is there no
implicit conversion from RefPtr<T> to T*?

+};
+
+} // namespace blink
+
+#endif // ReadableStreamController_h