[SCM] WebKit Debian packaging branch, webkit-1.1, updated. upstream/1.1.21-584-g1e41756

[ggaren at apple.com]

The following commit has been merged in the webkit-1.1 branch:
commit ebf857ca130d944e5aac436a2a9bd42ed0404cec
Author: ggaren at apple.com <ggaren at apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Date:   Fri Feb 12 05:01:07 2010 +0000

    2010-02-11  Geoffrey Garen  <ggaren at apple.com>
    
            Reviewed by Oliver Hunt and Darin Adler.
    
            The rest of the fix for
            https://bugs.webkit.org/show_bug.cgi?id=34864 | <rdar://problem/7594198>
            Many objects left uncollected after visiting mail.google.com and closing
            window
    
            Don't unconditionally hang onto small strings. Instead, hang onto all
            small strings as long as any small string is still referenced.
    
            SunSpider reports no change.
    
            * runtime/Collector.cpp:
            (JSC::Heap::markRoots): Mark the small strings cache last, so it can
            check if anything else has kept any strings alive.
    
            * runtime/SmallStrings.cpp:
            (JSC::isMarked):
            (JSC::SmallStrings::markChildren): Only keep our strings alive if some
            other reference to at least one of them exists, too.
    
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54701 268f45cc-cd09-0410-ab3c-d52691b4dbfc

diff --git a/JavaScriptCore/ChangeLog b/JavaScriptCore/ChangeLog
index 301e5aa..389bde6 100644
--- a/JavaScriptCore/ChangeLog
+++ b/JavaScriptCore/ChangeLog
@@ -1,5 +1,28 @@
 2010-02-11  Geoffrey Garen  <ggaren at apple.com>
 
+        Reviewed by Oliver Hunt and Darin Adler.
+
+        The rest of the fix for
+        https://bugs.webkit.org/show_bug.cgi?id=34864 | <rdar://problem/7594198>
+        Many objects left uncollected after visiting mail.google.com and closing
+        window
+        
+        Don't unconditionally hang onto small strings. Instead, hang onto all
+        small strings as long as any small string is still referenced.
+        
+        SunSpider reports no change.
+
+        * runtime/Collector.cpp:
+        (JSC::Heap::markRoots): Mark the small strings cache last, so it can
+        check if anything else has kept any strings alive.
+
+        * runtime/SmallStrings.cpp:
+        (JSC::isMarked):
+        (JSC::SmallStrings::markChildren): Only keep our strings alive if some
+        other reference to at least one of them exists, too.
+
+2010-02-11  Geoffrey Garen  <ggaren at apple.com>
+
         Reviewed by Gavin Barraclough.
 
         Some progress toward fixing
diff --git a/JavaScriptCore/runtime/Collector.cpp b/JavaScriptCore/runtime/Collector.cpp
index a391d26..2873e0b 100644
--- a/JavaScriptCore/runtime/Collector.cpp
+++ b/JavaScriptCore/runtime/Collector.cpp
@@ -1122,12 +1122,15 @@ void Heap::markRoots()
         MarkedArgumentBuffer::markLists(markStack, *m_markListSet);
     if (m_globalData->exception)
         markStack.append(m_globalData->exception);
-    m_globalData->smallStrings.markChildren(markStack);
     if (m_globalData->functionCodeBlockBeingReparsed)
         m_globalData->functionCodeBlockBeingReparsed->markAggregate(markStack);
     if (m_globalData->firstStringifierToMark)
         JSONObject::markStringifiers(markStack, m_globalData->firstStringifierToMark);
 
+    // Mark the small strings cache last, since it will clear itself if nothing
+    // else has marked it.
+    m_globalData->smallStrings.markChildren(markStack);
+
     markStack.drain();
     markStack.compact();
 
diff --git a/JavaScriptCore/runtime/SmallStrings.cpp b/JavaScriptCore/runtime/SmallStrings.cpp
index d34307a..d9d4377 100644
--- a/JavaScriptCore/runtime/SmallStrings.cpp
+++ b/JavaScriptCore/runtime/SmallStrings.cpp
@@ -34,6 +34,11 @@
 namespace JSC {
 static const unsigned numCharactersToStore = 0x100;
 
+static inline bool isMarked(JSString* string)
+{
+    return string && Heap::isCellMarked(string);
+}
+
 class SmallStringsStorage : public Noncopyable {
 public:
     SmallStringsStorage();
@@ -66,6 +71,25 @@ SmallStrings::~SmallStrings()
 
 void SmallStrings::markChildren(MarkStack& markStack)
 {
+    /*
+       Our hypothesis is that small strings are very common. So, we cache them
+       to avoid GC churn. However, in cases where this hypothesis turns out to
+       be false -- including the degenerate case where all JavaScript execution
+       has terminated -- we don't want to waste memory.
+
+       To test our hypothesis, we check if any small string has been marked. If
+       so, it's probably reasonable to mark the rest. If not, we clear the cache.
+     */
+
+    bool isAnyStringMarked = isMarked(m_emptyString);
+    for (unsigned i = 0; i < numCharactersToStore && !isAnyStringMarked; ++i)
+        isAnyStringMarked |= isMarked(m_singleCharacterStrings[i]);
+    
+    if (!isAnyStringMarked) {
+        clear();
+        return;
+    }
+    
     if (m_emptyString)
         markStack.append(m_emptyString);
     for (unsigned i = 0; i < numCharactersToStore; ++i) {

-- 
WebKit Debian packaging