include/unotools/readwritemutexguard.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
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   5  * This Source Code Form is subject to the terms of the Mozilla Public
   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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  12  *   contributor license agreements. See the NOTICE file distributed
  13  *   with this work for additional information regarding copyright
  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 namespace ReadWriteGuardMode {
  52 const sal_Int32 nWrite          = 0x01;
  53 const sal_Int32 nCriticalChange = 0x02 | nWrite;
  54 const sal_Int32 nBlockCritical  = 0x04;     // only a block, not a read, exclusive flag!
  55 }
  56
  57 /** Enable multiple threads to read simultaneously, but a write blocks all
  58     other reads and writes, and a read blocks any write.
  59     Used in I18N wrappers to be able to maintain a single instance of a wrapper
  60     for the standard Office locale.
  61     NEVER construct a writing guard if there is already a reading guard in the
  62     same context, the following will dead lock EVEN IN THE SAME THREAD!
  63     void foo()
  64     {
  65         ReadWriteGuard aGuard1( aMutex );
  66         bar();
  67     }
  68     void bar()
  69     {
  70         // waits forever for aGuard1
  71         ReadWriteGuard aGuard2( aMutex, ReadWriteGuardMode::nWrite );
  72     }
  73  */
  74 class ReadWriteGuard
  75 {
  76             ReadWriteMutex&     rMutex;
  77             sal_Int32           nMode;
  78 public:
  79                                 ReadWriteGuard(
  80                                     ReadWriteMutex& rMutex,
  81                                     sal_Int32 nRequestMode = 0  // read only
  82                                     );
  83                                 ~ReadWriteGuard();
  84
  85     /** Be careful with this, it does wait for ANY read to complete.
  86         The following will dead lock EVEN IN THE SAME THREAD!
  87         void foo()
  88         {
  89             ReadWriteGuard aGuard1( aMutex );
  90             bar();
  91         }
  92         void bar()
  93         {
  94             ReadWriteGuard aGuard2( aMutex );
  95             aGuard2.changeReadToWrite();    // waits forever for aGuard1
  96         }
  97      */
  98             void                changeReadToWrite();
  99 };
 100
 101 }   // namespace utl
 102
 103 #endif // INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
 104
 105 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */