include/wx/thrimpl.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        include/wx/thrimpl.cpp
   3 // Purpose:     common part of wxThread Implementations
   4 // Author:      Vadim Zeitlin
   5 // Modified by:
   6 // Created:     04.06.02 (extracted from src/*/thread.cpp files)
   7 // RCS-ID:      $Id$
   8 // Copyright:   (c) Vadim Zeitlin (2002)
   9 // Licence:     wxWindows licence
  10 /////////////////////////////////////////////////////////////////////////////
  11
  12 // this file is supposed to be included only by the various thread.cpp
  13
  14 // ----------------------------------------------------------------------------
  15 // wxMutex
  16 // ----------------------------------------------------------------------------
  17
  18 wxMutex::wxMutex(wxMutexType mutexType)
  19 {
  20     m_internal = new wxMutexInternal(mutexType);
  21
  22     if ( !m_internal->IsOk() )
  23     {
  24         delete m_internal;
  25         m_internal = NULL;
  26     }
  27 }
  28
  29 wxMutex::~wxMutex()
  30 {
  31     delete m_internal;
  32 }
  33
  34 bool wxMutex::IsOk() const
  35 {
  36     return m_internal != NULL;
  37 }
  38
  39 wxMutexError wxMutex::Lock()
  40 {
  41     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  42                  _T("wxMutex::Lock(): not initialized") );
  43
  44     return m_internal->Lock();
  45 }
  46
  47 wxMutexError wxMutex::TryLock()
  48 {
  49     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  50                  _T("wxMutex::TryLock(): not initialized") );
  51
  52     return m_internal->TryLock();
  53 }
  54
  55 wxMutexError wxMutex::Unlock()
  56 {
  57     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  58                  _T("wxMutex::Unlock(): not initialized") );
  59
  60     return m_internal->Unlock();
  61 }
  62
  63 // --------------------------------------------------------------------------
  64 // wxConditionInternal
  65 // --------------------------------------------------------------------------
  66
  67 // Win32 and OS/2 don't have explicit support for the POSIX condition
  68 // variables and their events/event semaphores have quite different semantics,
  69 // so we reimplement the conditions from scratch using the mutexes and
  70 // semaphores
  71 #if defined(__WXMSW__) || defined(__OS2__) || defined(__EMX__)
  72
  73 class wxConditionInternal
  74 {
  75 public:
  76     wxConditionInternal(wxMutex& mutex);
  77
  78     bool IsOk() const { return m_mutex.IsOk() && m_semaphore.IsOk(); }
  79
  80     wxCondError Wait();
  81     wxCondError WaitTimeout(unsigned long milliseconds);
  82
  83     wxCondError Signal();
  84     wxCondError Broadcast();
  85
  86 private:
  87     // the number of threads currently waiting for this condition
  88     LONG m_numWaiters;
  89
  90     // the critical section protecting m_numWaiters
  91     wxCriticalSection m_csWaiters;
  92
  93     wxMutex& m_mutex;
  94     wxSemaphore m_semaphore;
  95
  96     DECLARE_NO_COPY_CLASS(wxConditionInternal)
  97 };
  98
  99 wxConditionInternal::wxConditionInternal(wxMutex& mutex)
 100                    : m_mutex(mutex)
 101 {
 102     // another thread can't access it until we return from ctor, so no need to
 103     // protect access to m_numWaiters here
 104     m_numWaiters = 0;
 105 }
 106
 107 wxCondError wxConditionInternal::Wait()
 108 {
 109     // increment the number of waiters
 110     {
 111         wxCriticalSectionLocker lock(m_csWaiters);
 112         m_numWaiters++;
 113     }
 114
 115     m_mutex.Unlock();
 116
 117     // a potential race condition can occur here
 118     //
 119     // after a thread increments nwaiters, and unlocks the mutex and before the
 120     // semaphore.Wait() is called, if another thread can cause a signal to be
 121     // generated
 122     //
 123     // this race condition is handled by using a semaphore and incrementing the
 124     // semaphore only if 'nwaiters' is greater that zero since the semaphore,
 125     // can 'remember' signals the race condition will not occur
 126
 127     // wait ( if necessary ) and decrement semaphore
 128     wxSemaError err = m_semaphore.Wait();
 129     m_mutex.Lock();
 130
 131     if ( err == wxSEMA_NO_ERROR )
 132         return wxCOND_NO_ERROR;
 133     else if ( err == wxSEMA_TIMEOUT )
 134         return wxCOND_TIMEOUT;
 135     else
 136         return wxCOND_MISC_ERROR;
 137 }
 138
 139 wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
 140 {
 141     {
 142         wxCriticalSectionLocker lock(m_csWaiters);
 143         m_numWaiters++;
 144     }
 145
 146     m_mutex.Unlock();
 147
 148     // a race condition can occur at this point in the code
 149     //
 150     // please see the comments in Wait(), for details
 151
 152     wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
 153
 154     if ( err == wxSEMA_TIMEOUT )
 155     {
 156         // another potential race condition exists here it is caused when a
 157         // 'waiting' thread timesout, and returns from WaitForSingleObject, but
 158         // has not yet decremented 'nwaiters'.
 159         //
 160         // at this point if another thread calls signal() then the semaphore
 161         // will be incremented, but the waiting thread will miss it.
 162         //
 163         // to handle this particular case, the waiting thread calls
 164         // WaitForSingleObject again with a timeout of 0, after locking
 165         // 'nwaiters_mutex'. this call does not block because of the zero
 166         // timeout, but will allow the waiting thread to catch the missed
 167         // signals.
 168         wxCriticalSectionLocker lock(m_csWaiters);
 169
 170         err = m_semaphore.WaitTimeout(0);
 171
 172         if ( err != wxSEMA_NO_ERROR )
 173         {
 174             m_numWaiters--;
 175         }
 176     }
 177
 178     m_mutex.Lock();
 179
 180     return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR
 181                                   : err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT
 182                                                           : wxCOND_MISC_ERROR;
 183 }
 184
 185 wxCondError wxConditionInternal::Signal()
 186 {
 187     wxCriticalSectionLocker lock(m_csWaiters);
 188
 189     if ( m_numWaiters > 0 )
 190     {
 191         // increment the semaphore by 1
 192         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 193             return wxCOND_MISC_ERROR;
 194
 195         m_numWaiters--;
 196     }
 197
 198     return wxCOND_NO_ERROR;
 199 }
 200
 201 wxCondError wxConditionInternal::Broadcast()
 202 {
 203     wxCriticalSectionLocker lock(m_csWaiters);
 204
 205     while ( m_numWaiters > 0 )
 206     {
 207         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 208             return wxCOND_MISC_ERROR;
 209
 210         m_numWaiters--;
 211     }
 212
 213     return wxCOND_NO_ERROR;
 214 }
 215
 216 #endif // MSW or OS2
 217
 218 // ----------------------------------------------------------------------------
 219 // wxCondition
 220 // ----------------------------------------------------------------------------
 221
 222 wxCondition::wxCondition(wxMutex& mutex)
 223 {
 224     m_internal = new wxConditionInternal(mutex);
 225
 226     if ( !m_internal->IsOk() )
 227     {
 228         delete m_internal;
 229         m_internal = NULL;
 230     }
 231 }
 232
 233 wxCondition::~wxCondition()
 234 {
 235     delete m_internal;
 236 }
 237
 238 bool wxCondition::IsOk() const
 239 {
 240     return m_internal != NULL;
 241 }
 242
 243 wxCondError wxCondition::Wait()
 244 {
 245     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 246                  _T("wxCondition::Wait(): not initialized") );
 247
 248     return m_internal->Wait();
 249 }
 250
 251 wxCondError wxCondition::WaitTimeout(unsigned long milliseconds)
 252 {
 253     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 254                  _T("wxCondition::Wait(): not initialized") );
 255
 256     return m_internal->WaitTimeout(milliseconds);
 257 }
 258
 259 wxCondError wxCondition::Signal()
 260 {
 261     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 262                  _T("wxCondition::Signal(): not initialized") );
 263
 264     return m_internal->Signal();
 265 }
 266
 267 wxCondError wxCondition::Broadcast()
 268 {
 269     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 270                  _T("wxCondition::Broadcast(): not initialized") );
 271
 272     return m_internal->Broadcast();
 273 }
 274
 275 // --------------------------------------------------------------------------
 276 // wxSemaphore
 277 // --------------------------------------------------------------------------
 278
 279 wxSemaphore::wxSemaphore(int initialcount, int maxcount)
 280 {
 281     m_internal = new wxSemaphoreInternal( initialcount, maxcount );
 282     if ( !m_internal->IsOk() )
 283     {
 284         delete m_internal;
 285         m_internal = NULL;
 286     }
 287 }
 288
 289 wxSemaphore::~wxSemaphore()
 290 {
 291     delete m_internal;
 292 }
 293
 294 bool wxSemaphore::IsOk() const
 295 {
 296     return m_internal != NULL;
 297 }
 298
 299 wxSemaError wxSemaphore::Wait()
 300 {
 301     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 302                  _T("wxSemaphore::Wait(): not initialized") );
 303
 304     return m_internal->Wait();
 305 }
 306
 307 wxSemaError wxSemaphore::TryWait()
 308 {
 309     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 310                  _T("wxSemaphore::TryWait(): not initialized") );
 311
 312     return m_internal->TryWait();
 313 }
 314
 315 wxSemaError wxSemaphore::WaitTimeout(unsigned long milliseconds)
 316 {
 317     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 318                  _T("wxSemaphore::WaitTimeout(): not initialized") );
 319
 320     return m_internal->WaitTimeout(milliseconds);
 321 }
 322
 323 wxSemaError wxSemaphore::Post()
 324 {
 325     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 326                  _T("wxSemaphore::Post(): not initialized") );
 327
 328     return m_internal->Post();
 329 }
 330