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      1 /*
      2  * libjingle
      3  * Copyright 2009, 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_FILELOCK_H_
     29 #define TALK_BASE_FILELOCK_H_
     30 
     31 #include <string>
     32 
     33 #include "talk/base/constructormagic.h"
     34 #include "talk/base/scoped_ptr.h"
     35 
     36 namespace talk_base {
     37 
     38 class FileStream;
     39 
     40 // Implements a very simple cross process lock based on a file.
     41 // When Lock(...) is called we try to open/create the file in read/write
     42 // mode without any sharing. (Or locking it with flock(...) on Unix)
     43 // If the process crash the OS will make sure that the file descriptor
     44 // is released and another process can accuire the lock.
     45 // This doesn't work on ancient OSX/Linux versions if used on NFS.
     46 // (Nfs-client before: ~2.6 and Linux Kernel < 2.6.)
     47 class FileLock {
     48  public:
     49   virtual ~FileLock();
     50 
     51   // Attempts to lock the file. The caller owns the returned
     52   // lock object. Returns NULL if the file already was locked.
     53   static FileLock* TryLock(const std::string& path);
     54   void Unlock();
     55 
     56  protected:
     57   FileLock(const std::string& path, FileStream* file);
     58 
     59  private:
     60   void MaybeUnlock();
     61 
     62   std::string path_;
     63   scoped_ptr<FileStream> file_;
     64 
     65   DISALLOW_EVIL_CONSTRUCTORS(FileLock);
     66 };
     67 
     68 }  // namespace talk_base
     69 
     70 #endif  // TALK_BASE_FILELOCK_H_
     71