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::LockTimeout(unsigned long ms)
  48 {
  49     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  50                  _T("wxMutex::Lock(): not initialized") );
  51
  52     return m_internal->Lock(ms);
  53 }
  54
  55 wxMutexError wxMutex::TryLock()
  56 {
  57     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  58                  _T("wxMutex::TryLock(): not initialized") );
  59
  60     return m_internal->TryLock();
  61 }
  62
  63 wxMutexError wxMutex::Unlock()
  64 {
  65     wxCHECK_MSG( m_internal, wxMUTEX_INVALID,
  66                  _T("wxMutex::Unlock(): not initialized") );
  67
  68     return m_internal->Unlock();
  69 }
  70
  71 // --------------------------------------------------------------------------
  72 // wxConditionInternal
  73 // --------------------------------------------------------------------------
  74
  75 // Win32 and OS/2 don't have explicit support for the POSIX condition
  76 // variables and their events/event semaphores have quite different semantics,
  77 // so we reimplement the conditions from scratch using the mutexes and
  78 // semaphores
  79 #if defined(__WXMSW__) || defined(__OS2__) || defined(__EMX__)
  80
  81 class wxConditionInternal
  82 {
  83 public:
  84     wxConditionInternal(wxMutex& mutex);
  85
  86     bool IsOk() const { return m_mutex.IsOk() && m_semaphore.IsOk(); }
  87
  88     wxCondError Wait();
  89     wxCondError WaitTimeout(unsigned long milliseconds);
  90
  91     wxCondError Signal();
  92     wxCondError Broadcast();
  93
  94 private:
  95     // the number of threads currently waiting for this condition
  96     LONG m_numWaiters;
  97
  98     // the critical section protecting m_numWaiters
  99     wxCriticalSection m_csWaiters;
 100
 101     wxMutex& m_mutex;
 102     wxSemaphore m_semaphore;
 103
 104     DECLARE_NO_COPY_CLASS(wxConditionInternal)
 105 };
 106
 107 wxConditionInternal::wxConditionInternal(wxMutex& mutex)
 108                    : m_mutex(mutex)
 109 {
 110     // another thread can't access it until we return from ctor, so no need to
 111     // protect access to m_numWaiters here
 112     m_numWaiters = 0;
 113 }
 114
 115 wxCondError wxConditionInternal::Wait()
 116 {
 117     // increment the number of waiters
 118     {
 119         wxCriticalSectionLocker lock(m_csWaiters);
 120         m_numWaiters++;
 121     }
 122
 123     m_mutex.Unlock();
 124
 125     // a potential race condition can occur here
 126     //
 127     // after a thread increments m_numWaiters, and unlocks the mutex and before
 128     // the semaphore.Wait() is called, if another thread can cause a signal to
 129     // be generated
 130     //
 131     // this race condition is handled by using a semaphore and incrementing the
 132     // semaphore only if m_numWaiters is greater that zero since the semaphore,
 133     // can 'remember' signals the race condition will not occur
 134
 135     // wait ( if necessary ) and decrement semaphore
 136     wxSemaError err = m_semaphore.Wait();
 137     m_mutex.Lock();
 138
 139     if ( err == wxSEMA_NO_ERROR )
 140         return wxCOND_NO_ERROR;
 141     else if ( err == wxSEMA_TIMEOUT )
 142         return wxCOND_TIMEOUT;
 143     else
 144         return wxCOND_MISC_ERROR;
 145 }
 146
 147 wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
 148 {
 149     {
 150         wxCriticalSectionLocker lock(m_csWaiters);
 151         m_numWaiters++;
 152     }
 153
 154     m_mutex.Unlock();
 155
 156     // a race condition can occur at this point in the code
 157     //
 158     // please see the comments in Wait(), for details
 159
 160     wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
 161
 162     if ( err == wxSEMA_TIMEOUT )
 163     {
 164         // another potential race condition exists here it is caused when a
 165         // 'waiting' thread times out, and returns from WaitForSingleObject,
 166         // but has not yet decremented m_numWaiters
 167         //
 168         // at this point if another thread calls signal() then the semaphore
 169         // will be incremented, but the waiting thread will miss it.
 170         //
 171         // to handle this particular case, the waiting thread calls
 172         // WaitForSingleObject again with a timeout of 0, after locking
 173         // m_csWaiters. This call does not block because of the zero
 174         // timeout, but will allow the waiting thread to catch the missed
 175         // signals.
 176         wxCriticalSectionLocker lock(m_csWaiters);
 177
 178         wxSemaError err2 = m_semaphore.WaitTimeout(0);
 179
 180         if ( err2 != wxSEMA_NO_ERROR )
 181         {
 182             m_numWaiters--;
 183         }
 184     }
 185
 186     m_mutex.Lock();
 187
 188     return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR
 189                                   : err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT
 190                                                           : wxCOND_MISC_ERROR;
 191 }
 192
 193 wxCondError wxConditionInternal::Signal()
 194 {
 195     wxCriticalSectionLocker lock(m_csWaiters);
 196
 197     if ( m_numWaiters > 0 )
 198     {
 199         // increment the semaphore by 1
 200         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 201             return wxCOND_MISC_ERROR;
 202
 203         m_numWaiters--;
 204     }
 205
 206     return wxCOND_NO_ERROR;
 207 }
 208
 209 wxCondError wxConditionInternal::Broadcast()
 210 {
 211     wxCriticalSectionLocker lock(m_csWaiters);
 212
 213     while ( m_numWaiters > 0 )
 214     {
 215         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 216             return wxCOND_MISC_ERROR;
 217
 218         m_numWaiters--;
 219     }
 220
 221     return wxCOND_NO_ERROR;
 222 }
 223
 224 #endif // MSW or OS2
 225
 226 // ----------------------------------------------------------------------------
 227 // wxCondition
 228 // ----------------------------------------------------------------------------
 229
 230 wxCondition::wxCondition(wxMutex& mutex)
 231 {
 232     m_internal = new wxConditionInternal(mutex);
 233
 234     if ( !m_internal->IsOk() )
 235     {
 236         delete m_internal;
 237         m_internal = NULL;
 238     }
 239 }
 240
 241 wxCondition::~wxCondition()
 242 {
 243     delete m_internal;
 244 }
 245
 246 bool wxCondition::IsOk() const
 247 {
 248     return m_internal != NULL;
 249 }
 250
 251 wxCondError wxCondition::Wait()
 252 {
 253     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 254                  _T("wxCondition::Wait(): not initialized") );
 255
 256     return m_internal->Wait();
 257 }
 258
 259 wxCondError wxCondition::WaitTimeout(unsigned long milliseconds)
 260 {
 261     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 262                  _T("wxCondition::Wait(): not initialized") );
 263
 264     return m_internal->WaitTimeout(milliseconds);
 265 }
 266
 267 wxCondError wxCondition::Signal()
 268 {
 269     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 270                  _T("wxCondition::Signal(): not initialized") );
 271
 272     return m_internal->Signal();
 273 }
 274
 275 wxCondError wxCondition::Broadcast()
 276 {
 277     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 278                  _T("wxCondition::Broadcast(): not initialized") );
 279
 280     return m_internal->Broadcast();
 281 }
 282
 283 // --------------------------------------------------------------------------
 284 // wxSemaphore
 285 // --------------------------------------------------------------------------
 286
 287 wxSemaphore::wxSemaphore(int initialcount, int maxcount)
 288 {
 289     m_internal = new wxSemaphoreInternal( initialcount, maxcount );
 290     if ( !m_internal->IsOk() )
 291     {
 292         delete m_internal;
 293         m_internal = NULL;
 294     }
 295 }
 296
 297 wxSemaphore::~wxSemaphore()
 298 {
 299     delete m_internal;
 300 }
 301
 302 bool wxSemaphore::IsOk() const
 303 {
 304     return m_internal != NULL;
 305 }
 306
 307 wxSemaError wxSemaphore::Wait()
 308 {
 309     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 310                  _T("wxSemaphore::Wait(): not initialized") );
 311
 312     return m_internal->Wait();
 313 }
 314
 315 wxSemaError wxSemaphore::TryWait()
 316 {
 317     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 318                  _T("wxSemaphore::TryWait(): not initialized") );
 319
 320     return m_internal->TryWait();
 321 }
 322
 323 wxSemaError wxSemaphore::WaitTimeout(unsigned long milliseconds)
 324 {
 325     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 326                  _T("wxSemaphore::WaitTimeout(): not initialized") );
 327
 328     return m_internal->WaitTimeout(milliseconds);
 329 }
 330
 331 wxSemaError wxSemaphore::Post()
 332 {
 333     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 334                  _T("wxSemaphore::Post(): not initialized") );
 335
 336     return m_internal->Post();
 337 }
 338