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<title>[170499] trunk/Source/WebCore</title>
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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/170499">170499</a></dd>
<dt>Author</dt> <dd>akling@apple.com</dd>
<dt>Date</dt> <dd>2014-06-26 15:22:40 -0700 (Thu, 26 Jun 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Skip memcmp()ing fully downloaded resources after they become mmap()able.
<https://webkit.org/b/134362>
When we receive word that a downloaded resource is now available for mmap()ing
from the file system, we don't need to compare against the buffered data,
since even if there were a mismatch, the cached version should be the canonical one.
This was added as belt-and-suspenders while the supporting mechanism was being
developed in CFNetwork, and there's no evidence of a race today. This change
turns the runtime checks into debug-only assertions.
Saves ~300ms of main thread time on PLT.
Reviewed by Geoff Garen.
* loader/cache/CachedResource.cpp:
(WebCore::CachedResource::tryReplaceEncodedData):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreloadercacheCachedResourcecpp">trunk/Source/WebCore/loader/cache/CachedResource.cpp</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (170498 => 170499)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2014-06-26 22:18:57 UTC (rev 170498)
+++ trunk/Source/WebCore/ChangeLog 2014-06-26 22:22:40 UTC (rev 170499)
</span><span class="lines">@@ -1,3 +1,23 @@
</span><ins>+2014-06-26 Andreas Kling <akling@apple.com>
+
+ Skip memcmp()ing fully downloaded resources after they become mmap()able.
+ <https://webkit.org/b/134362>
+
+ When we receive word that a downloaded resource is now available for mmap()ing
+ from the file system, we don't need to compare against the buffered data,
+ since even if there were a mismatch, the cached version should be the canonical one.
+
+ This was added as belt-and-suspenders while the supporting mechanism was being
+ developed in CFNetwork, and there's no evidence of a race today. This change
+ turns the runtime checks into debug-only assertions.
+
+ Saves ~300ms of main thread time on PLT.
+
+ Reviewed by Geoff Garen.
+
+ * loader/cache/CachedResource.cpp:
+ (WebCore::CachedResource::tryReplaceEncodedData):
+
</ins><span class="cx"> 2014-06-26 Jer Noble <jer.noble@apple.com>
</span><span class="cx">
</span><span class="cx"> [MSE] Refactoring: Use C++11 for-loops in SourceBuffer.
</span></span></pre></div>
<a id="trunkSourceWebCoreloadercacheCachedResourcecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/loader/cache/CachedResource.cpp (170498 => 170499)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/loader/cache/CachedResource.cpp 2014-06-26 22:18:57 UTC (rev 170498)
+++ trunk/Source/WebCore/loader/cache/CachedResource.cpp 2014-06-26 22:22:40 UTC (rev 170499)
</span><span class="lines">@@ -900,12 +900,10 @@
</span><span class="cx">
</span><span class="cx"> if (!mayTryReplaceEncodedData())
</span><span class="cx"> return;
</span><del>-
- // Because the disk cache is asynchronous and racey with regards to the data we might be asked to replace,
- // we need to verify that the new buffer has the same contents as our old buffer.
- if (m_data->size() != newBuffer->size() || memcmp(m_data->data(), newBuffer->data(), m_data->size()))
- return;
</del><span class="cx">
</span><ins>+ ASSERT(m_data->size() == newBuffer->size());
+ ASSERT(!memcmp(m_data->data(), newBuffer->data(), m_data->size()));
+
</ins><span class="cx"> m_data->tryReplaceSharedBufferContents(newBuffer.get());
</span><span class="cx"> }
</span><span class="cx"> #endif
</span></span></pre>
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