Changeset 44325 in webkit for trunk/JavaScriptCore/runtime/UString.cpp

Timestamp:

Jun 1, 2009, 11:41:20 AM (16 years ago)

Author:

[email protected]

Message:

JavaScriptCore:

2009-06-01 David Levin <​[email protected]>

Reviewed by Darin Alder and Maciej Stachowiak.

Bug 26057: StringImpl should share buffers with UString.
​https://bugs.webkit.org/show_bug.cgi?id=26057

• JavaScriptCore.exp:
• runtime/UString.cpp: (JSC::UString::Rep::create): (JSC::UString::BaseString::sharedBuffer): Only do the sharing when the buffer exceeds a certain size. The size was tuned by running various dom benchmarks with numbers ranging from 20 to 800 and finding a place that seemed to do the best overall.
• runtime/UString.h:

WebCore:

2009-06-01 David Levin <​[email protected]>

Reviewed by Darin Alder and Maciej Stachowiak.

Bug 26057: StringImpl should share buffers with UString.
​https://bugs.webkit.org/show_bug.cgi?id=26057

This change results in the following performance improvements:
On ​http://www.hixie.ch/tests/adhoc/perf/dom/artificial/core/001.html
the time went from 78ms to 40ms for append (other times remained constant).

On ​http://www.hixie.ch/tests/adhoc/perf/dom/artificial/core/002.html,
the time went from 3900ms to 2600ms.

For ​http://dromaeo.com/?dom, the time for DomModification improved by ~6%.
Other tests in dom seemed to be faster across several runs but within the
margin of error (except DOM Attributes which was slightly ~1.5% worse).

Existing tests cover this code and there is no new functionality
that is exposed to test.

• platform/text/AtomicString.cpp: (WebCore::AtomicString::add):
• platform/text/String.cpp: (WebCore::String::String): (WebCore::String::operator UString):
• platform/text/StringImpl.cpp: (WebCore::StringImpl::StringImpl): (WebCore::StringImpl::~StringImpl): (WebCore::StringImpl::create): Consumes a shared buffer. (WebCore::StringImpl::ustring): Shares the StringImpl's buffer with the UString. (WebCore::StringImpl::sharedBuffer): Exposes the buffer that may be shared.
• platform/text/StringImpl.h: (WebCore::StringImpl::hasTerminatingNullCharacter): (WebCore::StringImpl::inTable): (WebCore::StringImpl::setInTable): Converted the bools to be inside of PtrAndFlags to avoid growing StringImpl in size.

File:

• trunk/JavaScriptCore/runtime/UString.cpp (modified) (3 diffs)

trunk/JavaScriptCore/runtime/UString.cpp

@@ -63 +63 @@
 extern const double Inf;
 
+// This number must be at least 2 to avoid sharing empty, null as well as 1 character strings from SmallStrings.
+static const int minLengthToShare = 30;
+
 static inline size_t overflowIndicator() { return std::numeric_limits<size_t>::max(); }
 static inline size_t maxUChars() { return std::numeric_limits<size_t>::max() / sizeof(UChar); }
@@ -233 +236 @@
 }
 
-PassRefPtr<UString::Rep> UString::Rep::share(UChar* string, int length, PassRefPtr<UString::SharedUChar> sharedBuffer)
+PassRefPtr<UString::Rep> UString::Rep::create(UChar* string, int length, PassRefPtr<UString::SharedUChar> sharedBuffer)
 {
     PassRefPtr<UString::Rep> rep = create(string, length);
@@ -383 +386 @@
 UString::SharedUChar* UString::BaseString::sharedBuffer()
 {
-    // Don't share empty, null and 1 character strings from SmallStrings.
-    if (len <= 1)
+
+    if (len < minLengthToShare)
         return 0;