New lock implementation for mac

webrtc/base/criticalsection.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 11 matching lines @@
 // exists as two separate projects, webrtc and libjingle.
 #include <winsock2.h>
 #include <windows.h>
 #include <sal.h>  // must come after windows headers.
 #endif  // defined(WEBRTC_WIN)
 
 #if defined(WEBRTC_POSIX)
 #include <pthread.h>
 #endif
 
+// See notes in the 'Performance' unit test for the effects of this flag.
+#define USE_NATIVE_MUTEX_ON_MAC 0
+
+#if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
+#include <dispatch/dispatch.h>
+#endif
+
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
 #define CS_DEBUG_CHECKS 1
 #endif
 
 #if CS_DEBUG_CHECKS
 #define CS_DEBUG_CODE(x) x
 #else  // !CS_DEBUG_CHECKS
 #define CS_DEBUG_CODE(x)
 #endif  // !CS_DEBUG_CHECKS
 
@@ skipping 10 matching lines @@
 
   // Use only for RTC_DCHECKing.
   bool CurrentThreadIsOwner() const;
   // Use only for RTC_DCHECKing.
   bool IsLocked() const;
 
  private:
 #if defined(WEBRTC_WIN)
   CRITICAL_SECTION crit_;
 #elif defined(WEBRTC_POSIX)
+#if defined(WEBRTC_MAC) && !USE_NATIVE_MUTEX_ON_MAC
+  // Number of times the lock has been locked + number of threads waiting.
+  // TODO(tommi): We could use this number and subtract the recursion count
+  // to find places where we have multiple threads contending on the same lock.
+  volatile int lock_queue_;
+  // |recursion_| represents the recursion count + 1 for the thread that owns
+  // the lock. Only modified by the thread that owns the lock.
+  int recursion_;
+  // Used to signal a single waiting thread when the lock becomes available.
+  dispatch_semaphore_t semaphore_;
+  // The thread that currently holds the lock. Required to handle recursion.
+  pthread_t owning_thread_;
+#else
   pthread_mutex_t mutex_;
+#endif
   CS_DEBUG_CODE(pthread_t thread_);
   CS_DEBUG_CODE(int recursion_count_);
 #endif
 };
 
 // CritScope, for serializing execution through a scope.
 class SCOPED_LOCKABLE CritScope {
  public:
   explicit CritScope(CriticalSection* cs) EXCLUSIVE_LOCK_FUNCTION(cs);
   ~CritScope() UNLOCK_FUNCTION();
@@ skipping 47 matching lines @@
   explicit GlobalLockScope(GlobalLockPod* lock) EXCLUSIVE_LOCK_FUNCTION(lock);
   ~GlobalLockScope() UNLOCK_FUNCTION();
  private:
   GlobalLockPod* const lock_;
   RTC_DISALLOW_COPY_AND_ASSIGN(GlobalLockScope);
 };
 
 } // namespace rtc
 
 #endif // WEBRTC_BASE_CRITICALSECTION_H_