Stream scripts to V8 as they load - Blink side.

Source/bindings/core/v8/ScriptStreamer.h

+// Copyright 2014 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 ScriptStreamer_h
+#define ScriptStreamer_h
+
+#include "wtf/RefCounted.h"
+
+#include <v8.h>
+
+namespace blink {
+
+class PendingScript;
+class ScriptResource;
+class ScriptResourceClient;
+class SourceStream;
+
+// ScriptStreamer streams incomplete script data to V8 so that it can be parsed
+// while it's loaded. PendingScript holds a reference to ScriptStreamer. At the
+// moment, ScriptStreamer is only used for parser blocking scripts; this means
+// that the Document stays stable and no other scripts are executing while we're
+// streaming. It is possible, though, that Document and the PendingScript are
+// destroyed while the streaming is in progress, and ScriptStreamer handles it
+// gracefully.
+class ScriptStreamer : public RefCounted<ScriptStreamer> {
+public:
+    // Launches a task (on a background thread) which will stream the given
+    // PendingScript into V8 as it loads. It's also possible that V8 cannot
+    // stream the given script; in that case this function returns
+    // false. Internally, this constructs a ScriptStreamer and attaches it to
+    // the PendingScript. Use ScriptStreamer::addClient to get notified when the
+    // streaming finishes.
+    static bool startStreaming(PendingScript&);
+
+    bool streamingInProgress() const { return !m_loadingFinished || !m_v8Done; }
+
+    v8::ScriptCompiler::StreamedSource* source() { return &m_source; }
+    ScriptResource* resource() const { return m_resource; }
+
+    // Called when the upper layer doesn't need the streamed PendingScript any
+    // more. After calling cancel, the upper layer (PendingScript) can drop its

[haraken, 2014/09/10 05:57:51]

This comment is a bit confusing, though I know what you mean. What does the
"upper layer" mean? Is it a PendingScript?

[marja, 2014/09/11 09:15:37]

Clarified this:

    // Called when the script is not needed any more (e.g., loading was
    // cancelled). After calling cancel, PendingScript can drop its reference to
    // ScriptStreamer, and ScriptStreamer takes care of eventually deleting
    // itself (after the V8 side has finished too).

+    // reference to ScriptStreamer, and ScriptStreamer takes care of eventually
+    // deleting itself (after the V8 side has finished too).
+    void cancel();
+
+    // When the streaming is suppressed, the data is not given to V8, but
+    // ScriptStreamer still watches the resource load and notifies the upper
+    // layers when loading is finished. It is used in situations when we have
+    // started streaming but then we detect we don't want to stream (e.g., when
+    // we have the code cache for the script) and we still want to parse and
+    // execute it when it has finished loading.
+    void suppressStreaming() { m_streamingSuppressed = true; }
+    bool streamingSuppressed() const { return m_streamingSuppressed; }
+
+    unsigned cachedDataDataType() const { return m_cachedDataDataType; }
+
+    void addClient(ScriptResourceClient* client)
+    {
+        ASSERT(!m_client);
+        m_client = client;
+    }
+
+    void removeClient(ScriptResourceClient* client)
+    {
+        ASSERT(m_client == client);
+        m_client = 0;
+    }
+
+    // Called by PendingScript when data arrives from the network.
+    void notifyAppendData();
+    void notifyFinished();
+
+    // Called by ScriptStreamingTask when it has streamed all data to V8 and V8
+    // has processed it.
+    void streamingComplete();
+
+private:
+    ScriptStreamer(ScriptResource*, v8::ScriptCompiler::StreamedSource::Encoding);
+
+    void notifyFinishedToClient();
+
+    // This pointer is weak. If PendingScript and its Resource are deleted
+    // before ScriptStreamer, PendingScript will notify ScriptStreamer of its
+    // deletion by calling cancel().
+    ScriptResource* m_resource;

[haraken, 2014/09/10 05:57:51]

Can we avoid adding the m_resource member to ScriptStreamer? In cases where a
ScriptStreamer wants to use a ScriptResource, you can pass the ScriptResource
explicitly to the ScriptStreamer's methods.

[marja, 2014/09/11 09:15:37]

We need it in e.g., notifyFinishedToClient which might get called when the V8
side finishes, so at that point, nobody can pass the Resource to ScriptStreamer
(unless ScriptStreamerTask or something like that holds a pointer to it, but I
don't think it's any better).

+
+    SourceStream* m_stream;
+    v8::ScriptCompiler::StreamedSource m_source;
+    ScriptResourceClient* m_client;
+    bool m_loadingFinished; // Whether loading from the network is done.
+    bool m_v8Done; // Whether the V8 side processing is done.

[haraken, 2014/09/10 05:57:51]

m_v8Done => m_parsingFinished ? (for consistency with m_loadingFinished)

[marja, 2014/09/11 09:15:37]

Done.

+
+    // Whether the script source code should be retrieved from the Resource
+    // instead of the ScriptStreamer.
+    bool m_streamingSuppressed;
+
+    // What kind of cached data V8 produces during streaming.
+    unsigned m_cachedDataDataType;

[haraken, 2014/09/10 05:57:51]

m_cachedDataDataType => m_cachedDataType ?

[marja, 2014/09/11 09:15:37]

Done.

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