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      1 /*
      2  * libjingle
      3  * Copyright 2011, Google Inc.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions are met:
      7  *
      8  *  1. Redistributions of source code must retain the above copyright notice,
      9  *     this list of conditions and the following disclaimer.
     10  *  2. Redistributions in binary form must reproduce the above copyright notice,
     11  *     this list of conditions and the following disclaimer in the documentation
     12  *     and/or other materials provided with the distribution.
     13  *  3. The name of the author may not be used to endorse or promote products
     14  *     derived from this software without specific prior written permission.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
     17  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     18  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
     19  * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     20  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     21  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
     22  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     23  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
     24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
     25  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     26  */
     27 
     28 #ifndef TALK_BASE_SHAREDEXCLUSIVELOCK_H_
     29 #define TALK_BASE_SHAREDEXCLUSIVELOCK_H_
     30 
     31 #include "talk/base/constructormagic.h"
     32 #include "talk/base/criticalsection.h"
     33 #include "talk/base/event.h"
     34 
     35 namespace talk_base {
     36 
     37 // This class provides shared-exclusive lock. It can be used in cases like
     38 // multiple-readers/single-writer model.
     39 class SharedExclusiveLock {
     40  public:
     41   SharedExclusiveLock();
     42 
     43   // Locking/unlocking methods. It is encouraged to use SharedScope or
     44   // ExclusiveScope for protection.
     45   void LockExclusive();
     46   void UnlockExclusive();
     47   void LockShared();
     48   void UnlockShared();
     49 
     50  private:
     51   talk_base::CriticalSection cs_exclusive_;
     52   talk_base::CriticalSection cs_shared_;
     53   talk_base::Event shared_count_is_zero_;
     54   int shared_count_;
     55 
     56   DISALLOW_COPY_AND_ASSIGN(SharedExclusiveLock);
     57 };
     58 
     59 class SharedScope {
     60  public:
     61   explicit SharedScope(SharedExclusiveLock* lock) : lock_(lock) {
     62     lock_->LockShared();
     63   }
     64 
     65   ~SharedScope() {
     66     lock_->UnlockShared();
     67   }
     68 
     69  private:
     70   SharedExclusiveLock* lock_;
     71 
     72   DISALLOW_COPY_AND_ASSIGN(SharedScope);
     73 };
     74 
     75 class ExclusiveScope {
     76  public:
     77   explicit ExclusiveScope(SharedExclusiveLock* lock) : lock_(lock) {
     78     lock_->LockExclusive();
     79   }
     80 
     81   ~ExclusiveScope() {
     82     lock_->UnlockExclusive();
     83   }
     84 
     85  private:
     86   SharedExclusiveLock* lock_;
     87 
     88   DISALLOW_COPY_AND_ASSIGN(ExclusiveScope);
     89 };
     90 
     91 }  // namespace talk_base
     92 
     93 #endif  // TALK_BASE_SHAREDEXCLUSIVELOCK_H_
     94