include/unotools/readwritemutexguard.hxx

   1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   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  *
  11  *   Licensed to the Apache Software Foundation (ASF) under one or more
  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 #include <o3tl/typed_flags_set.hxx>
  25
  26 enum class ReadWriteGuardMode {
  27     ReadOnly       = 0x00,
  28     Write          = 0x01,
  29     CriticalChange = 0x02 | Write,
  30     BlockCritical  = 0x04,     // only a block, not a read, exclusive flag!
  31 };
  32 namespace o3tl {
  33     template<> struct typed_flags<ReadWriteGuardMode> : is_typed_flags<ReadWriteGuardMode, 0x7> {};
  34 }
  35
  36 namespace utl {
  37
  38 class ReadWriteMutex
  39 {
  40     friend class ReadWriteGuard;
  41
  42             sal_uInt32          nReadCount;
  43             sal_uInt32          nBlockCriticalCount;
  44             ::osl::Mutex        maMutex;
  45             ::osl::Mutex        maWriteMutex;
  46
  47 public:
  48                                 ReadWriteMutex()
  49                                     : nReadCount(0)
  50                                     , nBlockCriticalCount(0)
  51                                     {}
  52 };
  53
  54 /** Enable multiple threads to read simultaneously, but a write blocks all
  55     other reads and writes, and a read blocks any write.
  56     Used in I18N wrappers to be able to maintain a single instance of a wrapper
  57     for the standard Office locale.
  58     NEVER construct a writing guard if there is already a reading guard in the
  59     same context, the following will dead lock EVEN IN THE SAME THREAD!
  60     void foo()
  61     {
  62         ReadWriteGuard aGuard1( aMutex );
  63         bar();
  64     }
  65     void bar()
  66     {
  67         // waits forever for aGuard1
  68         ReadWriteGuard aGuard2( aMutex, ReadWriteGuardMode::nWrite );
  69     }
  70  */
  71 class ReadWriteGuard
  72 {
  73             ReadWriteMutex&     rMutex;
  74             ReadWriteGuardMode  nMode;
  75 public:
  76                                 ReadWriteGuard(
  77                                     ReadWriteMutex& rMutex,
  78                                     ReadWriteGuardMode nRequestMode = ReadWriteGuardMode::ReadOnly  // read only
  79                                     );
  80                                 ~ReadWriteGuard();
  81
  82     /** Be careful with this, it does wait for ANY read to complete.
  83         The following will dead lock EVEN IN THE SAME THREAD!
  84         void foo()
  85         {
  86             ReadWriteGuard aGuard1( aMutex );
  87             bar();
  88         }
  89         void bar()
  90         {
  91             ReadWriteGuard aGuard2( aMutex );
  92             aGuard2.changeReadToWrite();    // waits forever for aGuard1
  93         }
  94      */
  95             void                changeReadToWrite();
  96 };
  97
  98 }   // namespace utl
  99
 100 #endif // INCLUDED_UNOTOOLS_READWRITEMUTEXGUARD_HXX
 101
 102 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */