Add histograms to ResourceFetcher to evaluate memory cache hit rate

Source/core/fetch/ResourceFetcher.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 207 matching lines @@
     ASSERT_NOT_REACHED();
     return ResourceRequest::TargetIsSubresource;
 }
 
 ResourceFetcher::ResourceFetcher(DocumentLoader* documentLoader)
     : m_document(0)
     , m_documentLoader(documentLoader)
     , m_requestCount(0)
     , m_garbageCollectDocumentResourcesTimer(this, &ResourceFetcher::garbageCollectDocumentResourcesTimerFired)
     , m_resourceTimingReportTimer(this, &ResourceFetcher::resourceTimingReportTimerFired)
+    , m_useCount(0)
+    , m_revalidateCount(0)
+    , m_loadCount(0)
     , m_autoLoadImages(true)
     , m_imagesEnabled(true)
     , m_allowStaleResources(false)
 {
 }
 
 ResourceFetcher::~ResourceFetcher()
 {
     m_documentLoader = 0;
     m_document = 0;
 
     clearPreloads();
 
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.HitCount", m_useCount, 0, 1000, 50);
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.RevalidateCount", m_revalidateCount, 0, 1000, 50);
+    blink::Platform::current()->histogramCustomCounts(
+        "WebCore.ResourceFetcher.LoadCount", m_loadCount, 0, 1000, 50);
+
     // Make sure no requests still point to this ResourceFetcher
     ASSERT(!m_requestCount);
 }
 
 Resource* ResourceFetcher::cachedResource(const KURL& resourceURL) const
 {
     KURL url = MemoryCache::removeFragmentIdentifierIfNeeded(resourceURL);
     return m_documentResources.get(url).get();
 }
 
@@ skipping 371 matching lines @@
     // See if we can use an existing resource from the cache.
     ResourcePtr<Resource> resource = memoryCache()->resourceForURL(url);
 
     const RevalidationPolicy policy = determineRevalidationPolicy(type, request.mutableResourceRequest(), request.forPreload(), resource.get(), request.defer());
     switch (policy) {
     case Reload:
         memoryCache()->remove(resource.get());
         // Fall through
     case Load:
         resource = loadResource(type, request, request.charset());
+        ++m_loadCount;

[Nate Chapin, 2014/01/28 20:22:54]

Would it be cleaner to wrap these variables up into a simple helper class owner
by ResourceFetcher?

I'd at least prefer that incrementing the appropriate counter be done in a
helper function, rather than in this switch statement.

[clamy, 2014/01/29 12:19:21]

Done.

         break;
     case Revalidate:
         resource = revalidateResource(request, resource.get());
+        if (!resource->hasClients())
+            ++m_revalidateCount;
         break;
     case Use:
         resource->updateForAccess();
         notifyLoadedFromMemoryCache(resource.get());
+        if (!resource->hasClients())
+            ++m_useCount;
         break;
     }
 
     if (!resource)
         return 0;
 
     if (policy != Use)
         resource->setIdentifier(createUniqueIdentifier());
 
     if (!request.forPreload() || policy != Use) {
@@ skipping 721 matching lines @@
 }
 #endif
 
 const ResourceLoaderOptions& ResourceFetcher::defaultResourceOptions()
 {
     DEFINE_STATIC_LOCAL(ResourceLoaderOptions, options, (SniffContent, BufferData, AllowStoredCredentials, ClientRequestedCredentials, AskClientForCrossOriginCredentials, DoSecurityCheck, CheckContentSecurityPolicy, DocumentContext));
     return options;
 }
 
 }