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_BUSY )
 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 : wxCOND_MISC_ERROR;
 178 }
 179
 180 wxCondError wxConditionInternal::Signal()
 181 {
 182     wxCriticalSectionLocker lock(m_csWaiters);
 183
 184     if ( m_numWaiters > 0 )
 185     {
 186         // increment the semaphore by 1
 187         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 188             return wxCOND_MISC_ERROR;
 189
 190         m_numWaiters--;
 191     }
 192
 193     return wxCOND_NO_ERROR;
 194 }
 195
 196 wxCondError wxConditionInternal::Broadcast()
 197 {
 198     wxCriticalSectionLocker lock(m_csWaiters);
 199
 200     while ( m_numWaiters > 0 )
 201     {
 202         if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
 203             return wxCOND_MISC_ERROR;
 204
 205         m_numWaiters--;
 206     }
 207
 208     return wxCOND_NO_ERROR;
 209 }
 210 #endif
 211
 212 // ----------------------------------------------------------------------------
 213 // wxCondition
 214 // ----------------------------------------------------------------------------
 215
 216 wxCondition::wxCondition(wxMutex& mutex)
 217 {
 218     m_internal = new wxConditionInternal(mutex);
 219
 220     if ( !m_internal->IsOk() )
 221     {
 222         delete m_internal;
 223         m_internal = NULL;
 224     }
 225 }
 226
 227 wxCondition::~wxCondition()
 228 {
 229     delete m_internal;
 230 }
 231
 232 bool wxCondition::IsOk() const
 233 {
 234     return m_internal != NULL;
 235 }
 236
 237 wxCondError wxCondition::Wait()
 238 {
 239     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 240                  _T("wxCondition::Wait(): not initialized") );
 241
 242     return m_internal->Wait();
 243 }
 244
 245 wxCondError wxCondition::WaitTimeout(unsigned long milliseconds)
 246 {
 247     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 248                  _T("wxCondition::Wait(): not initialized") );
 249
 250     return m_internal->WaitTimeout(milliseconds);
 251 }
 252
 253 wxCondError wxCondition::Signal()
 254 {
 255     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 256                  _T("wxCondition::Signal(): not initialized") );
 257
 258     return m_internal->Signal();
 259 }
 260
 261 wxCondError wxCondition::Broadcast()
 262 {
 263     wxCHECK_MSG( m_internal, wxCOND_INVALID,
 264                  _T("wxCondition::Broadcast(): not initialized") );
 265
 266     return m_internal->Broadcast();
 267 }
 268
 269 // --------------------------------------------------------------------------
 270 // wxSemaphore
 271 // --------------------------------------------------------------------------
 272
 273 wxSemaphore::wxSemaphore(int initialcount, int maxcount)
 274 {
 275     m_internal = new wxSemaphoreInternal( initialcount, maxcount );
 276     if ( !m_internal->IsOk() )
 277     {
 278         delete m_internal;
 279         m_internal = NULL;
 280     }
 281 }
 282
 283 wxSemaphore::~wxSemaphore()
 284 {
 285     delete m_internal;
 286 }
 287
 288 bool wxSemaphore::IsOk() const
 289 {
 290     return m_internal != NULL;
 291 }
 292
 293 wxSemaError wxSemaphore::Wait()
 294 {
 295     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 296                  _T("wxSemaphore::Wait(): not initialized") );
 297
 298     return m_internal->Wait();
 299 }
 300
 301 wxSemaError wxSemaphore::TryWait()
 302 {
 303     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 304                  _T("wxSemaphore::TryWait(): not initialized") );
 305
 306     return m_internal->TryWait();
 307 }
 308
 309 wxSemaError wxSemaphore::WaitTimeout(unsigned long milliseconds)
 310 {
 311     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 312                  _T("wxSemaphore::WaitTimeout(): not initialized") );
 313
 314     return m_internal->WaitTimeout(milliseconds);
 315 }
 316
 317 wxSemaError wxSemaphore::Post()
 318 {
 319     wxCHECK_MSG( m_internal, wxSEMA_INVALID,
 320                  _T("wxSemaphore::Post(): not initialized") );
 321
 322     return m_internal->Post();
 323 }
 324