Added VMCache::SwitchFromReadLock(), atomically unlocking a read lock and

starting to lock the cache.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34936 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vm/VMCache.h

@@ -73,6 +73,7 @@ public:
 	inline	bool				Lock();
 	inline	bool				TryLock();
 	inline	bool				SwitchLock(mutex* from);
+	inline	bool				SwitchFromReadLock(rw_lock* from);
 			void				Unlock();
 	inline	void				AssertLocked();
 
@@ -220,6 +221,13 @@ VMCache::SwitchLock(mutex* from)
 }
 
 
+bool
+VMCache::SwitchFromReadLock(rw_lock* from)
+{
+	return mutex_switch_from_read_lock(from, &fLock) == B_OK;
+}
+
+
 void
 VMCache::AssertLocked()
 {