diff --git a/JavaScriptCore/ChangeLog b/JavaScriptCore/ChangeLog
index cbc47ad3d8eff25a4416a937b190bfb617e79718..d0e490ea7dc4401965e879720a9c7478715ef738 100644
--- a/JavaScriptCore/ChangeLog
+++ b/JavaScriptCore/ChangeLog
@@ -1,3 +1,24 @@
+2009-06-12  Dave Hyatt  <hyatt@apple.com>
+
+        Reviewed by Anders Carlsson.
+
+        https://bugs.webkit.org/show_bug.cgi?id=26373
+
+        Add a new class to Threading in wtf called ReadWriteLock that handles single writer/multiple reader locking.
+        Provide a pthreads-only implementation of the lock for now, as this class is only going to be used
+        on Snow Leopard at first.
+
+        * wtf/Threading.h:
+        (WTF::ReadWriteLock::impl):
+        * wtf/ThreadingPthreads.cpp:
+        (WTF::ReadWriteLock::ReadWriteLock):
+        (WTF::ReadWriteLock::~ReadWriteLock):
+        (WTF::ReadWriteLock::readLock):
+        (WTF::ReadWriteLock::tryReadLock):
+        (WTF::ReadWriteLock::writeLock):
+        (WTF::ReadWriteLock::tryWriteLock):
+        (WTF::ReadWriteLock::unlock):
+
 2009-06-12  Oliver Hunt  <oliver@apple.com>
 
         Reviewed by Geoff Garen.
diff --git a/JavaScriptCore/wtf/Threading.h b/JavaScriptCore/wtf/Threading.h
index 02fa3a4cd70794f932052b613f6dca921a1bd498..d244768a88b2ad29c73506c9ae59291350a3a8b6 100644
--- a/JavaScriptCore/wtf/Threading.h
+++ b/JavaScriptCore/wtf/Threading.h
@@ -126,18 +126,22 @@ void detachThread(ThreadIdentifier);
 
 #if USE(PTHREADS)
 typedef pthread_mutex_t PlatformMutex;
+typedef pthread_rwlock_t PlatformReadWriteLock;
 typedef pthread_cond_t PlatformCondition;
 #elif PLATFORM(GTK)
 typedef GOwnPtr<GMutex> PlatformMutex;
+typedef void* PlatformReadWriteLock; // FIXME: Implement.
 typedef GOwnPtr<GCond> PlatformCondition;
 #elif PLATFORM(QT)
 typedef QT_PREPEND_NAMESPACE(QMutex)* PlatformMutex;
+typedef void* PlatformReadWriteLock; // FIXME: Implement.
 typedef QT_PREPEND_NAMESPACE(QWaitCondition)* PlatformCondition;
 #elif PLATFORM(WIN_OS)
 struct PlatformMutex {
     CRITICAL_SECTION m_internalMutex;
     size_t m_recursionCount;
 };
+typedef void* PlatformReadWriteLock; // FIXME: Implement.
 struct PlatformCondition {
     size_t m_waitersGone;
     size_t m_waitersBlocked;
@@ -151,6 +155,7 @@ struct PlatformCondition {
 };
 #else
 typedef void* PlatformMutex;
+typedef void* PlatformReadWriteLock;
 typedef void* PlatformCondition;
 #endif
     
@@ -171,6 +176,23 @@ private:
 
 typedef Locker<Mutex> MutexLocker;
 
+class ReadWriteLock : Noncopyable {
+public:
+    ReadWriteLock();
+    ~ReadWriteLock();
+
+    void readLock();
+    bool tryReadLock();
+
+    void writeLock();
+    bool tryWriteLock();
+    
+    void unlock();
+
+private:
+    PlatformReadWriteLock m_readWriteLock;
+};
+
 class ThreadCondition : Noncopyable {
 public:
     ThreadCondition();
diff --git a/JavaScriptCore/wtf/ThreadingPthreads.cpp b/JavaScriptCore/wtf/ThreadingPthreads.cpp
index f54dd3f8322b54a38327204d7d860c87f0cdd2fd..d0e6df8fb7bc7d8a203e22a94356883003f07fce 100644
--- a/JavaScriptCore/wtf/ThreadingPthreads.cpp
+++ b/JavaScriptCore/wtf/ThreadingPthreads.cpp
@@ -267,6 +267,61 @@ void Mutex::unlock()
     ASSERT_UNUSED(result, !result);
 }
 
+
+ReadWriteLock::ReadWriteLock()
+{
+    pthread_rwlock_init(&m_readWriteLock, NULL);
+}
+
+ReadWriteLock::~ReadWriteLock()
+{
+    pthread_rwlock_destroy(&m_readWriteLock);
+}
+
+void ReadWriteLock::readLock()
+{
+    int result = pthread_rwlock_rdlock(&m_readWriteLock);
+    ASSERT_UNUSED(result, !result);
+}
+
+bool ReadWriteLock::tryReadLock()
+{
+    int result = pthread_rwlock_tryrdlock(&m_readWriteLock);
+
+    if (result == 0)
+        return true;
+    if (result == EBUSY || result == EAGAIN)
+        return false;
+
+    ASSERT_NOT_REACHED();
+    return false;
+}
+
+void ReadWriteLock::writeLock()
+{
+    int result = pthread_rwlock_wrlock(&m_readWriteLock);
+    ASSERT_UNUSED(result, !result);
+}
+
+bool ReadWriteLock::tryWriteLock()
+{
+    int result = pthread_rwlock_trywrlock(&m_readWriteLock);
+
+    if (result == 0)
+        return true;
+    if (result == EBUSY || result == EAGAIN)
+        return false;
+
+    ASSERT_NOT_REACHED();
+    return false;
+}
+
+void ReadWriteLock::unlock()
+{
+    int result = pthread_rwlock_unlock(&m_readWriteLock);
+    ASSERT_UNUSED(result, !result);
+}
+
 ThreadCondition::ThreadCondition()
 { 
     pthread_cond_init(&m_condition, NULL);