[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 {
 
+// To throttle readystatechange event fired when readystatechange is not
+// changed, we don't dispatch the event within 50ms.
+// As dispatching readystatechange when readystatechange is NOT changed is not
+// specified, 50ms is not specified, too.
+// We choose this value because progress event is dispatched every 50ms, but
+// actually this value doesn't have to equal to the interval.
+// Note: When readystate is actually changed readystatechange event must be
+// dispatched no matter how recently dispatched the event was.
+const double readyStateChangeFireInterval = 0.05;
+
 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_previousReadyStateChangeFireTime(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 231 matching lines @@
 void XMLHttpRequest::trackProgress(int length)
 {
     m_receivedLength += length;
 
     if (m_async)
         dispatchProgressEventFromSnapshot(EventTypeNames::progress);
 
     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();
+        // FIXME: Make our implementation and the spec consistent. This extra
+        // invocation of readystatechange event in LOADING state was needed
+        // when the progress event was not available.
+        double now = monotonicallyIncreasingTime();
+        bool shouldFire = now - m_previousReadyStateChangeFireTime >= readyStateChangeFireInterval;
+        if (shouldFire) {
+            m_previousReadyStateChangeFireTime = now;
+            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