src/Utils/RWSection.cpp

   1 // TortoiseSVN - a Windows shell extension for easy version control\r
   2 \r
   3 // Copyright (C) 2003-2008 - TortoiseSVN\r
   4 \r
   5 // This program is free software; you can redistribute it and/or\r
   6 // modify it under the terms of the GNU General Public License\r
   7 // as published by the Free Software Foundation; either version 2\r
   8 // of the License, or (at your option) any later version.\r
   9 \r
  10 // This program is distributed in the hope that it will be useful,\r
  11 // but WITHOUT ANY WARRANTY; without even the implied warranty of\r
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\r
  13 // GNU General Public License for more details.\r
  14 \r
  15 // You should have received a copy of the GNU General Public License\r
  16 // along with this program; if not, write to the Free Software Foundation,\r
  17 // 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.\r
  18 //\r
  19 #include "StdAfx.h"\r
  20 #include "RWSection.h"\r
  21 \r
  22 CRWSection::CRWSection()\r
  23 {\r
  24         m_nWaitingReaders = m_nWaitingWriters = m_nActive = 0;\r
  25         m_hReaders = CreateSemaphore(NULL, 0, MAXLONG, NULL);\r
  26         m_hWriters = CreateSemaphore(NULL, 0, MAXLONG, NULL);\r
  27         InitializeCriticalSection(&m_cs);\r
  28 }\r
  29 \r
  30 CRWSection::~CRWSection()\r
  31 {\r
  32 #ifdef _DEBUG\r
  33         if (m_nActive != 0)\r
  34                 DebugBreak();\r
  35 #endif\r
  36 \r
  37         m_nWaitingReaders = m_nWaitingWriters = m_nActive = 0;\r
  38         DeleteCriticalSection(&m_cs);\r
  39         CloseHandle(m_hWriters);\r
  40         CloseHandle(m_hReaders);\r
  41 }\r
  42 \r
  43 bool CRWSection::WaitToRead(DWORD waitTime)\r
  44 {\r
  45         EnterCriticalSection(&m_cs);\r
  46 \r
  47         // Writers have priority\r
  48         BOOL fResourceWritePending = (m_nWaitingWriters || (m_nActive < 0));\r
  49 \r
  50         if (fResourceWritePending)\r
  51         {\r
  52                 m_nWaitingReaders++;\r
  53         } \r
  54         else \r
  55         {\r
  56                 m_nActive++;\r
  57         }\r
  58 \r
  59         LeaveCriticalSection(&m_cs);\r
  60 \r
  61         if (fResourceWritePending)\r
  62         {\r
  63                 // wait until writer is finished\r
  64                 if (WaitForSingleObject(m_hReaders, waitTime) != WAIT_OBJECT_0)\r
  65                 {\r
  66                         EnterCriticalSection(&m_cs);\r
  67                         m_nWaitingReaders--;\r
  68                         LeaveCriticalSection(&m_cs);\r
  69                         return false;\r
  70                 }\r
  71         }\r
  72         return true;\r
  73 }\r
  74 \r
  75 bool CRWSection::WaitToWrite(DWORD waitTime)\r
  76 {\r
  77         EnterCriticalSection(&m_cs);\r
  78 \r
  79         BOOL fResourceOwned = (m_nActive != 0);\r
  80 \r
  81         if (fResourceOwned)\r
  82         {\r
  83                 m_nWaitingWriters++;\r
  84         } \r
  85         else \r
  86         {\r
  87                 m_nActive = -1;\r
  88         }\r
  89 \r
  90         LeaveCriticalSection(&m_cs);\r
  91 \r
  92         if (fResourceOwned)\r
  93         {\r
  94                 if (WaitForSingleObject(m_hWriters, waitTime) != WAIT_OBJECT_0)\r
  95                 {\r
  96                         EnterCriticalSection(&m_cs);\r
  97                         m_nWaitingWriters--;\r
  98                         LeaveCriticalSection(&m_cs);\r
  99                         return false;\r
 100                 }\r
 101         }\r
 102         return true;\r
 103 }\r
 104 \r
 105 void CRWSection::Done()\r
 106 {\r
 107         EnterCriticalSection(&m_cs);\r
 108 \r
 109         if (m_nActive > 0)\r
 110         {\r
 111                 m_nActive--;\r
 112         }\r
 113         else\r
 114         {\r
 115                 m_nActive++;\r
 116         }\r
 117 \r
 118         HANDLE hsem = NULL;\r
 119         LONG lCount = 1;\r
 120 \r
 121         if (m_nActive == 0)\r
 122         {\r
 123                 // Note: If there are always writers waiting, then\r
 124                 // it's possible that a reader never gets access\r
 125                 // (reader starvation)\r
 126                 if (m_nWaitingWriters > 0)\r
 127                 {\r
 128                         m_nActive = -1;\r
 129                         m_nWaitingWriters--;\r
 130                         hsem = m_hWriters;\r
 131                 }\r
 132                 else if (m_nWaitingReaders > 0)\r
 133                 {\r
 134                         m_nActive = m_nWaitingReaders;\r
 135                         m_nWaitingReaders = 0;\r
 136                         hsem = m_hReaders;\r
 137                         lCount = m_nActive;\r
 138                 }\r
 139                 else\r
 140                 {\r
 141                         // no threads waiting, nothing to do\r
 142                 }\r
 143         }\r
 144 \r
 145         LeaveCriticalSection(&m_cs);\r
 146 \r
 147         if (hsem != NULL)\r
 148         {\r
 149                 ReleaseSemaphore(hsem, lCount, NULL);\r
 150         }\r
 151 }\r
 152 \r