[XHR] Reduce 'readystatechange' event firing.

Source/core/xml/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 40 matching lines @@
 #include "platform/SharedBuffer.h"
 #include "platform/blob/BlobData.h"
 #include "platform/network/HTTPParsers.h"
 #include "platform/network/ParsedContentType.h"
 #include "platform/network/ResourceError.h"
 #include "platform/network/ResourceRequest.h"
 #include "public/platform/WebURLRequest.h"
 #include "wtf/ArrayBuffer.h"
 #include "wtf/ArrayBufferView.h"
 #include "wtf/Assertions.h"
+#include "wtf/CurrentTime.h"
 #include "wtf/RefCountedLeakCounter.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/text/CString.h"
 
 namespace blink {
 
+namespace {
+
+const double progressFireInterval = 0.05; // 0.05s
+const int progressFireMinimumSize = 1024 * 1024; // 1MB
+
+} // namespace
+
 DEFINE_DEBUG_ONLY_GLOBAL(WTF::RefCountedLeakCounter, xmlHttpRequestCounter, ("XMLHttpRequest"));
 
 struct XMLHttpRequestStaticData {
     WTF_MAKE_NONCOPYABLE(XMLHttpRequestStaticData); WTF_MAKE_FAST_ALLOCATED;
 public:
     XMLHttpRequestStaticData();
     String m_proxyHeaderPrefix;
     String m_secHeaderPrefix;
     HashSet<String, CaseFoldingHash> m_forbiddenRequestHeaders;
 };
@@ skipping 85 matching lines @@
     : ActiveDOMObject(context)
     , m_timeoutMilliseconds(0)
     , m_state(UNSENT)
     , m_downloadedBlobLength(0)
     , m_receivedLength(0)
     , m_lastSendLineNumber(0)
     , m_exceptionCode(0)
     , m_progressEventThrottle(this)
     , m_responseTypeCode(ResponseTypeDefault)
     , m_securityOrigin(securityOrigin)
+    , m_previousProgressFireTime(0)
+    , m_previousProgressRemainLength(0)
     , m_async(true)
     , m_includeCredentials(false)
     , m_createdDocument(false)
     , m_error(false)
     , m_uploadEventsAllowed(true)
     , m_uploadComplete(false)
     , m_sameOriginRequest(true)
 {
     initializeXMLHttpRequestStaticData();
 #ifndef NDEBUG
@@ skipping 224 matching lines @@
 XMLHttpRequestUpload* XMLHttpRequest::upload()
 {
     if (!m_upload)
         m_upload = XMLHttpRequestUpload::create(this);
     return m_upload.get();
 }
 
 void XMLHttpRequest::trackProgress(int length)
 {
     m_receivedLength += length;
+    double now = monotonicallyIncreasingTime();
+    bool shouldFire =
+        now - m_previousProgressFireTime >= progressFireInterval || m_previousProgressRemainLength + length >= progressFireMinimumSize;

[tyoshino (SeeGerritForStatus), 2014/07/29 11:39:37]

one line?

[yhirano, 2014/07/29 12:33:48]

Done.

+    if (shouldFire) {
+        m_previousProgressFireTime = now;
+        m_previousProgressRemainLength = 0;
+    } else {
+        m_previousProgressRemainLength += length;
+    }
 
-    if (m_async)
+    if (m_async && shouldFire)
         dispatchProgressEventFromSnapshot(EventTypeNames::progress);

[tyoshino (SeeGerritForStatus), 2014/07/29 11:39:37]

progress events are already throttled. the algorithm you're introducing is
different from one used by ProgressEventThrottler but seems good enough for
keeping apps that depend on extra dispatching of readystatechange events. we
could just apply shouldFire to dispatchReadyStateChangeEvent() call but not
here.

i'm concerned a little with inconsistency of timing between progressevents and
readystatechange events. hopefully as I suggested in the bug the frequency and
timing of extra readystatechange events should be limited but aligned exactly to
one of progressevent. do you think it's feasible?

[yhirano, 2014/07/29 12:33:48]

Done.
As discussed, we don't have to care about the consistency between these two
events.

 
     if (m_state != LOADING) {
         changeState(LOADING);
     } else {
-        // Firefox calls readyStateChanged every time it receives data. Do
-        // the same to align with Firefox.
-        //
         // FIXME: Make our implementation and the spec consistent. This
         // behavior was needed when the progress event was not available.
-        dispatchReadyStateChangeEvent();
+        if (shouldFire)
+            dispatchReadyStateChangeEvent();
     }
 }
 
 void XMLHttpRequest::changeState(State newState)
 {
     if (m_state != newState) {
         m_state = newState;
         dispatchReadyStateChangeEvent();
     }
 }
@@ skipping 985 matching lines @@
 {
     visitor->trace(m_responseBlob);
     visitor->trace(m_responseStream);
     visitor->trace(m_responseDocument);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     XMLHttpRequestEventTarget::trace(visitor);
 }
 
 } // namespace blink