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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/212566">212566</a></dd>
<dt>Author</dt> <dd>matthew_hanson@apple.com</dd>
<dt>Date</dt> <dd>2017-02-17 12:54:22 -0800 (Fri, 17 Feb 2017)</dd>
</dl>
<h3>Log Message</h3>
<pre>rdar://problem/30553220</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#branchessafari603branchSourceJavaScriptCoreChangeLog">branches/safari-603-branch/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#branchessafari603branchSourceJavaScriptCoreruntimeOptionscpp">branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.cpp</a></li>
<li><a href="#branchessafari603branchSourceJavaScriptCoreruntimeOptionsh">branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="branchessafari603branchSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: branches/safari-603-branch/Source/JavaScriptCore/ChangeLog (212565 => 212566)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-603-branch/Source/JavaScriptCore/ChangeLog 2017-02-17 20:38:46 UTC (rev 212565)
+++ branches/safari-603-branch/Source/JavaScriptCore/ChangeLog 2017-02-17 20:54:22 UTC (rev 212566)
</span><span class="lines">@@ -1,3 +1,23 @@
</span><ins>+2017-02-16 JF Bastien <jfbastien@apple.com>
+
+ A/B test concurrent GC
+ https://bugs.webkit.org/show_bug.cgi?id=168453
+
+ Reviewed by Filip Pizlo and Alexey Proskuryakov.
+
+ Landed by Matthew Hanson.
+
+ The concurrent GC may be causing more crashes, but it's hard to
+ tell. A/B test this by setting it off for 50% of users, based on
+ the UUID which crash tracer generates. From this we can look at
+ crashes and figure out whether the concurrent GC was on or off,
+ and derive whether fewer crashes occur when it's off.
+
+ * runtime/Options.cpp:
+ (getUserUUID):
+ (JSC::recomputeDependentOptions):
+ * runtime/Options.h:
+
</ins><span class="cx"> 2017-02-16 Keith Miller <keith_miller@apple.com>
</span><span class="cx">
</span><span class="cx"> Fix merge issue with r212085 (rdar://problem/29939864).
</span></span></pre></div>
<a id="branchessafari603branchSourceJavaScriptCoreruntimeOptionscpp"></a>
<div class="modfile"><h4>Modified: branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.cpp (212565 => 212566)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.cpp 2017-02-17 20:38:46 UTC (rev 212565)
+++ branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.cpp 2017-02-17 20:54:22 UTC (rev 212566)
</span><span class="lines">@@ -43,6 +43,40 @@
</span><span class="cx"> #include <wtf/StringExtras.h>
</span><span class="cx"> #include <wtf/text/StringBuilder.h>
</span><span class="cx">
</span><ins>+#if OS(DARWIN) && USE(APPLE_INTERNAL_SDK)
+#include <dlfcn.h>
+#include <CoreFoundation/CFString.h>
+#include <SystemConfiguration/SystemConfiguration.h>
+#include <WebCore/SoftLinking.h>
+SOFT_LINK_PRIVATE_FRAMEWORK(CrashReporterSupport);
+SOFT_LINK(CrashReporterSupport, CRGetUserUUID, CFStringRef, (void), ());
+static const char* getUserUUID()
+{
+ static CFStringRef (*softLinkCRGetUserUUID)(void);
+ static constexpr const size_t maxBytes = 37;
+ static char userUUID[maxBytes] = { '\0' };
+ static bool failed = true;
+ static std::once_flag once;
+ std::call_once(once, [] {
+ softLinkCRGetUserUUID = (CFStringRef (*)(void)) dlsym(CrashReporterSupportLibrary(), "CRGetUserUUID");
+ if (!softLinkCRGetUserUUID) {
+ dataLog("Failed getting user UUID: ", dlerror(), "\n");
+ return;
+ }
+ CFStringRef userUUIDString = CRGetUserUUID();
+ CFIndex length = CFStringGetLength(userUUIDString);
+ CFRange range = CFRangeMake(0, length);
+ CFIndex numConvertedCharacters = CFStringGetBytes(userUUIDString, range, kCFStringEncodingASCII, 0, false, reinterpret_cast<UInt8*>(userUUID), maxBytes - 1, nullptr);
+ if (numConvertedCharacters <= 0 || static_cast<size_t>(numConvertedCharacters) >= maxBytes) {
+ dataLog("Failed getting user UUID: ", numConvertedCharacters, numConvertedCharacters, maxBytes, "\n");
+ return;
+ }
+ failed = false;
+ });
+ return failed ? nullptr : userUUID;
+}
+#endif
+
</ins><span class="cx"> #if PLATFORM(COCOA)
</span><span class="cx"> #include <crt_externs.h>
</span><span class="cx"> #endif
</span><span class="lines">@@ -350,6 +384,29 @@
</span><span class="cx"> #if !CPU(X86_64) && !CPU(ARM64)
</span><span class="cx"> Options::useConcurrentGC() = false;
</span><span class="cx"> #endif
</span><ins>+#if OS(DARWIN) && USE(APPLE_INTERNAL_SDK)
+ if (Options::enableABTesting() && Options::useConcurrentGC()) {
+ // Run an A/B test on concurrent GC: if it was going to be on, turn it
+ // off with some probability. Do this deterministically per unique user
+ // identifier so that crashes don't skew statistics, and do it in a
+ // manner which can be reconstructed from a crash trace.
+ uint32_t accumulator = 0;
+ const char* userUUID = getUserUUID();
+ if (!userUUID) {
+ dataLog("A/B test: not setting useConcurrentGC because we failed to obtain the user UUID\n");
+ } else {
+ for (const char* c = userUUID; *c; ++c)
+ accumulator += *c;
+ accumulator = (accumulator & 0xFFFFu) ^ (accumulator >> 16);
+ accumulator = (accumulator & 0xFF) ^ (accumulator >> 8);
+ accumulator = (accumulator & 0xF) ^ (accumulator >> 4);
+ accumulator = (accumulator & 0x3) ^ (accumulator >> 2);
+ accumulator = (accumulator & 0x1) ^ (accumulator >> 1);
+ Options::useConcurrentGC() = accumulator;
+ dataLog("A/B test: setting useConcurrentGC to ", Options::useConcurrentGC(), " based on user UUID ", userUUID, "\n");
+ }
+ }
+#endif
</ins><span class="cx">
</span><span class="cx"> #if OS(WINDOWS) && CPU(X86)
</span><span class="cx"> // Disable JIT on Windows if SSE2 is not present
</span></span></pre></div>
<a id="branchessafari603branchSourceJavaScriptCoreruntimeOptionsh"></a>
<div class="modfile"><h4>Modified: branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.h (212565 => 212566)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.h 2017-02-17 20:38:46 UTC (rev 212565)
+++ branches/safari-603-branch/Source/JavaScriptCore/runtime/Options.h 2017-02-17 20:54:22 UTC (rev 212566)
</span><span class="lines">@@ -417,6 +417,8 @@
</span><span class="cx"> v(bool, useCodeCache, true, Normal, "If false, the unlinked byte code cache will not be used.") \
</span><span class="cx"> \
</span><span class="cx"> v(bool, useWebAssembly, false, Normal, "Expose the WebAssembly global object.") \
</span><ins>+ \
+ v(bool, enableABTesting, true, Normal, "If true, A/B testing will be performed to modify options, if false no A/B testing will be performed.") \
</ins><span class="cx">
</span><span class="cx"> enum OptionEquivalence {
</span><span class="cx"> SameOption,
</span></span></pre>
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