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 #if defined(__WXMSW__) || defined(__OS2__) || defined(__EMX__)
  68 // Win32 and OS/2 don't have explicit support for the POSIX condition
  69 // variables and their events/event semaphores have quite different semantics,
  70 // so we reimplement the conditions from scratch using the mutexes and
  71 // semaphores
  72 #if defined(__OS2__) || defined(__EMX__)
  73 void InterlockedIncrement(LONG *num)
  74 {
  75   ::DosEnterCritSec();
  76   (*num)++;
  77   ::DosExitCritSec();
  78 }
  79 #endif
  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     ::InterlockedIncrement(&m_numWaiters);
 119
 120     m_mutex.Unlock();
 121
 122     // a potential race condition can occur here
 123     //
 124     // after a thread increments nwaiters, and unlocks the mutex and before the
 125     // semaphore.Wait() is called, if another thread can cause a signal to be
 126     // generated
 127     //
 128     // this race condition is handled by using a semaphore and incrementing the
 129     // semaphore only if 'nwaiters' is greater that zero since the semaphore,
 130     // can 'remember' signals the race condition will not occur
 131
 132     // wait ( if necessary ) and decrement semaphore
 133     wxSemaError err = m_semaphore.Wait();
 134     m_mutex.Lock();
 135
 136     return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR : wxCOND_MISC_ERROR;
 137 }
 138
 139 wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
 140 {
 141     ::InterlockedIncrement(&m_numWaiters);
 142
 143     m_mutex.Unlock();
 144
 145     // a race condition can occur at this point in the code
 146     //
 147     // please see the comments in Wait(), for details
 148
 149     wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
 150
 151     if ( err == wxSEMA_TIMEOUT )
 152     {
 153         // another potential race condition exists here it is caused when a
 154         // 'waiting' thread timesout, and returns from WaitForSingleObject, but
 155         // has not yet decremented 'nwaiters'.
 156         //
 157         // at this point if another thread calls signal() then the semaphore
 158         // will be incremented, but the waiting thread will miss it.
 159         //
 160         // to handle this particular case, the waiting thread calls
 161         // WaitForSingleObject again with a timeout of 0, after locking
 162         // 'nwaiters_mutex'. this call does not block because of the zero
 163         // timeout, but will allow the waiting thread to catch the missed
 164         // signals.
 165         wxCriticalSectionLocker lock(m_csWaiters);
 166
 167         err = m_semaphore.WaitTimeout(0);
 168
 169         if ( err != wxSEMA_NO_ERROR )
 170         {
 171             m_numWaiters--;
 172         }
 173     }
 174
 175     m_mutex.Lock();
 176
 177     return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR
 178                                   : err == wxSEMA_TIMEOUT ? wxCOND_TIMEOUT
 179                                                           : wxCOND_MISC_ERROR;
 180 }
 181
 182 wxCondError wxConditionInternal::Signal()
 183 {
 184     wxCriticalSectionLocker lock(m_csWaiters);
 185
 186     if ( m_numWaiters > 0 )
 187     {
 188         // increment the semaphore by 1
 189         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 190             return wxCOND_MISC_ERROR;
 191
 192         m_numWaiters--;
 193     }
 194
 195     return wxCOND_NO_ERROR;
 196 }
 197
 198 wxCondError wxConditionInternal::Broadcast()
 199 {
 200     wxCriticalSectionLocker lock(m_csWaiters);
 201
 202     while ( m_numWaiters > 0 )
 203     {
 204         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 205             return wxCOND_MISC_ERROR;
 206
 207         m_numWaiters--;
 208     }
 209
 210     return wxCOND_NO_ERROR;
 211 }
 212 #endif
 213
 214 // ----------------------------------------------------------------------------
 215 // wxCondition
 216 // ----------------------------------------------------------------------------
 217
 218 wxCondition::wxCondition(wxMutex& mutex)
 219 {
 220     m_internal = new wxConditionInternal(mutex);
 221
 222     if ( !m_internal->IsOk() )
 223     {
 224         delete m_internal;
 225         m_internal = NULL;
 226     }
 227 }
 228
 229 wxCondition::~wxCondition()
 230 {
 231     delete m_internal;
 232 }
 233
 234 bool wxCondition::IsOk() const
 235 {
 236     return m_internal != NULL;
 237 }
 238
 239 wxCondError wxCondition::Wait()
 240 {
 241     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 242                  _T("wxCondition::Wait(): not initialized") );
 243
 244     return m_internal->Wait();
 245 }
 246
 247 wxCondError wxCondition::WaitTimeout(unsigned long milliseconds)
 248 {
 249     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 250                  _T("wxCondition::Wait(): not initialized") );
 251
 252     return m_internal->WaitTimeout(milliseconds);
 253 }
 254
 255 wxCondError wxCondition::Signal()
 256 {
 257     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 258                  _T("wxCondition::Signal(): not initialized") );
 259
 260     return m_internal->Signal();
 261 }
 262
 263 wxCondError wxCondition::Broadcast()
 264 {
 265     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 266                  _T("wxCondition::Broadcast(): not initialized") );
 267
 268     return m_internal->Broadcast();
 269 }
 270
 271 // --------------------------------------------------------------------------
 272 // wxSemaphore
 273 // --------------------------------------------------------------------------
 274
 275 wxSemaphore::wxSemaphore(int initialcount, int maxcount)
 276 {
 277     m_internal = new wxSemaphoreInternal( initialcount, maxcount );
 278     if ( !m_internal->IsOk() )
 279     {
 280         delete m_internal;
 281         m_internal = NULL;
 282     }
 283 }
 284
 285 wxSemaphore::~wxSemaphore()
 286 {
 287     delete m_internal;
 288 }
 289
 290 bool wxSemaphore::IsOk() const
 291 {
 292     return m_internal != NULL;
 293 }
 294
 295 wxSemaError wxSemaphore::Wait()
 296 {
 297     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 298                  _T("wxSemaphore::Wait(): not initialized") );
 299
 300     return m_internal->Wait();
 301 }
 302
 303 wxSemaError wxSemaphore::TryWait()
 304 {
 305     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 306                  _T("wxSemaphore::TryWait(): not initialized") );
 307
 308     return m_internal->TryWait();
 309 }
 310
 311 wxSemaError wxSemaphore::WaitTimeout(unsigned long milliseconds)
 312 {
 313     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 314                  _T("wxSemaphore::WaitTimeout(): not initialized") );
 315
 316     return m_internal->WaitTimeout(milliseconds);
 317 }
 318
 319 wxSemaError wxSemaphore::Post()
 320 {
 321     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 322                  _T("wxSemaphore::Post(): not initialized") );
 323
 324     return m_internal->Post();
 325 }
 326