include/unotools/readwritemutexguard.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
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   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
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  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 #ifndef INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
  21 #define INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
  22
  23 #include <osl/mutex.hxx>
  24
  25 namespace utl {
  26
  27 class ReadWriteGuard;
  28 class ReadWriteMutex
  29 {
  30     friend class ReadWriteGuard;
  31
  32             sal_uInt32          nReadCount;
  33             sal_uInt32          nBlockCriticalCount;
  34             ::osl::Mutex*       pMutex;
  35             ::osl::Mutex*       pWriteMutex;
  36
  37 public:
  38                                 ReadWriteMutex()
  39                                     : nReadCount(0)
  40                                     , nBlockCriticalCount(0)
  41                                     , pMutex( new ::osl::Mutex )
  42                                     , pWriteMutex( new ::osl::Mutex )
  43                                     {}
  44                                 ~ReadWriteMutex()
  45                                     {
  46                                         delete pMutex;
  47                                         delete pWriteMutex;
  48                                     }
  49 };
  50
  51
  52 namespace ReadWriteGuardMode {
  53 const sal_Int32 nWrite          = 0x01;
  54 const sal_Int32 nCriticalChange = 0x02 | nWrite;
  55 const sal_Int32 nBlockCritical  = 0x04;     // only a block, not a read, exclusive flag!
  56 }
  57
  58 /** Enable multiple threads to read simultaneously, but a write blocks all
  59     other reads and writes, and a read blocks any write.
  60     Used in I18N wrappers to be able to maintain a single instance of a wrapper
  61     for the standard Office locale.
  62     NEVER construct a writing guard if there is already a reading guard in the
  63     same context, the following will dead lock EVEN IN THE SAME THREAD!
  64     void foo()
  65     {
  66         ReadWriteGuard aGuard1( aMutex );
  67         bar();
  68     }
  69     void bar()
  70     {
  71         // waits forever for aGuard1
  72         ReadWriteGuard aGuard2( aMutex, ReadWriteGuardMode::nWrite );
  73     }
  74  */
  75 class ReadWriteGuard
  76 {
  77             ReadWriteMutex&     rMutex;
  78             sal_Int32           nMode;
  79 public:
  80                                 ReadWriteGuard(
  81                                     ReadWriteMutex& rMutex,
  82                                     sal_Int32 nRequestMode = 0  // read only
  83                                     );
  84                                 ~ReadWriteGuard();
  85
  86     /** Be careful with this, it does wait for ANY read to complete.
  87         The following will dead lock EVEN IN THE SAME THREAD!
  88         void foo()
  89         {
  90             ReadWriteGuard aGuard1( aMutex );
  91             bar();
  92         }
  93         void bar()
  94         {
  95             ReadWriteGuard aGuard2( aMutex );
  96             aGuard2.changeReadToWrite();    // waits forever for aGuard1
  97         }
  98      */
  99             void                changeReadToWrite();
 100 };
 101
 102 }   // namespace utl
 103
 104 #endif // INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
 105
 106 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */