Adds a modified copy of talk/base to webrtc/base. It is the first step in migrating talk/base to webrtc/base.

BUG=N/A
R=andrew@webrtc.org, wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6107 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/base/sharedexclusivelock.h

@@ -0,0 +1,76 @@
+/*
+ *  Copyright 2011 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.
+ */
+
+#ifndef WEBRTC_BASE_SHAREDEXCLUSIVELOCK_H_
+#define WEBRTC_BASE_SHAREDEXCLUSIVELOCK_H_
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/base/event.h"
+
+namespace rtc {
+
+// This class provides shared-exclusive lock. It can be used in cases like
+// multiple-readers/single-writer model.
+class SharedExclusiveLock {
+ public:
+  SharedExclusiveLock();
+
+  // Locking/unlocking methods. It is encouraged to use SharedScope or
+  // ExclusiveScope for protection.
+  void LockExclusive();
+  void UnlockExclusive();
+  void LockShared();
+  void UnlockShared();
+
+ private:
+  rtc::CriticalSection cs_exclusive_;
+  rtc::CriticalSection cs_shared_;
+  rtc::Event shared_count_is_zero_;
+  int shared_count_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedExclusiveLock);
+};
+
+class SharedScope {
+ public:
+  explicit SharedScope(SharedExclusiveLock* lock) : lock_(lock) {
+    lock_->LockShared();
+  }
+
+  ~SharedScope() {
+    lock_->UnlockShared();
+  }
+
+ private:
+  SharedExclusiveLock* lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedScope);
+};
+
+class ExclusiveScope {
+ public:
+  explicit ExclusiveScope(SharedExclusiveLock* lock) : lock_(lock) {
+    lock_->LockExclusive();
+  }
+
+  ~ExclusiveScope() {
+    lock_->UnlockExclusive();
+  }
+
+ private:
+  SharedExclusiveLock* lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExclusiveScope);
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_SHAREDEXCLUSIVELOCK_H_