[XHR] Reduce 'readystatechange' event firing.

Source/core/xml/XMLHttpRequest.cpp

Index: Source/core/xml/XMLHttpRequest.cpp
diff --git a/Source/core/xml/XMLHttpRequest.cpp b/Source/core/xml/XMLHttpRequest.cpp
index 3e6bf6c9ed6e875d727eb210fdd20f233c178433..ea943c9983d1c5f9a5ccaa9f48e417af22f8de06 100644
--- a/Source/core/xml/XMLHttpRequest.cpp
+++ b/Source/core/xml/XMLHttpRequest.cpp
@@ -58,12 +58,20 @@
 #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 {
@@ -169,6 +177,8 @@ XMLHttpRequest::XMLHttpRequest(ExecutionContext* context, PassRefPtr<SecurityOri
     , m_progressEventThrottle(this)
     , m_responseTypeCode(ResponseTypeDefault)
     , m_securityOrigin(securityOrigin)
+    , m_previousProgressFireTime(0)
+    , m_previousProgressRemainLength(0)
     , m_async(true)
     , m_includeCredentials(false)
     , m_createdDocument(false)
@@ -413,19 +423,26 @@ XMLHttpRequestUpload* XMLHttpRequest::upload()
 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();
     }
 }