src/msw/thread.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        thread.cpp
   3 // Purpose:     wxThread Implementation
   4 // Author:      Original from Wolfram Gloger/Guilhem Lavaux
   5 // Modified by: Vadim Zeitlin to make it work :-)
   6 // Created:     04/22/98
   7 // RCS-ID:      $Id$
   8 // Copyright:   (c) Wolfram Gloger (1996, 1997); Guilhem Lavaux (1998),
   9 //                  Vadim Zeitlin (1999)
  10 // Licence:     wxWindows licence
  11 /////////////////////////////////////////////////////////////////////////////
  12
  13 #ifdef __GNUG__
  14     #pragma implementation "thread.h"
  15 #endif
  16
  17 // ----------------------------------------------------------------------------
  18 // headers
  19 // ----------------------------------------------------------------------------
  20
  21 // For compilers that support precompilation, includes "wx.h".
  22 #include "wx/wxprec.h"
  23
  24 #if defined(__BORLANDC__)
  25     #pragma hdrstop
  26 #endif
  27
  28 #ifndef WX_PRECOMP
  29     #include "wx/wx.h"
  30 #endif
  31
  32 #if wxUSE_THREADS
  33
  34 #include <stdio.h>
  35
  36 #include <windows.h>
  37
  38 #include "wx/module.h"
  39 #include "wx/thread.h"
  40
  41 // the possible states of the thread ("=>" shows all possible transitions from
  42 // this state)
  43 enum wxThreadState
  44 {
  45     STATE_NEW,          // didn't start execution yet (=> RUNNING)
  46     STATE_RUNNING,      // thread is running (=> PAUSED, CANCELED)
  47     STATE_PAUSED,       // thread is temporarily suspended (=> RUNNING)
  48     STATE_CANCELED,     // thread should terminate a.s.a.p. (=> EXITED)
  49     STATE_EXITED        // thread is terminating
  50 };
  51
  52 // ----------------------------------------------------------------------------
  53 // static variables
  54 // ----------------------------------------------------------------------------
  55
  56 // TLS index of the slot where we store the pointer to the current thread
  57 static DWORD s_tlsThisThread = 0xFFFFFFFF;
  58
  59 // id of the main thread - the one which can call GUI functions without first
  60 // calling wxMutexGuiEnter()
  61 static DWORD s_idMainThread = 0;
  62
  63 // if it's FALSE, some secondary thread is holding the GUI lock
  64 static bool s_bGuiOwnedByMainThread = TRUE;
  65
  66 // critical section which controls access to all GUI functions: any secondary
  67 // thread (i.e. except the main one) must enter this crit section before doing
  68 // any GUI calls
  69 static wxCriticalSection *s_critsectGui = NULL;
  70
  71 // critical section which protects s_nWaitingForGui variable
  72 static wxCriticalSection *s_critsectWaitingForGui = NULL;
  73
  74 // number of threads waiting for GUI in wxMutexGuiEnter()
  75 static size_t s_nWaitingForGui = 0;
  76
  77 // are we waiting for a thread termination?
  78 static bool s_waitingForThread = FALSE;
  79
  80 // ============================================================================
  81 // Windows implementation of thread classes
  82 // ============================================================================
  83
  84 // ----------------------------------------------------------------------------
  85 // wxMutex implementation
  86 // ----------------------------------------------------------------------------
  87 class wxMutexInternal
  88 {
  89 public:
  90     HANDLE p_mutex;
  91 };
  92
  93 wxMutex::wxMutex()
  94 {
  95     p_internal = new wxMutexInternal;
  96     p_internal->p_mutex = CreateMutex(NULL, FALSE, NULL);
  97     if ( !p_internal->p_mutex )
  98     {
  99         wxLogSysError(_("Can not create mutex."));
 100     }
 101
 102     m_locked = 0;
 103 }
 104
 105 wxMutex::~wxMutex()
 106 {
 107     if (m_locked > 0)
 108         wxLogDebug("Warning: freeing a locked mutex (%d locks).", m_locked);
 109     CloseHandle(p_internal->p_mutex);
 110 }
 111
 112 wxMutexError wxMutex::Lock()
 113 {
 114     DWORD ret;
 115
 116     ret = WaitForSingleObject(p_internal->p_mutex, INFINITE);
 117     switch ( ret )
 118     {
 119         case WAIT_ABANDONED:
 120             return wxMUTEX_BUSY;
 121
 122         case WAIT_OBJECT_0:
 123             // ok
 124             break;
 125
 126         case WAIT_FAILED:
 127             wxLogSysError(_("Couldn't acquire a mutex lock"));
 128             return wxMUTEX_MISC_ERROR;
 129
 130         case WAIT_TIMEOUT:
 131         default:
 132             wxFAIL_MSG("impossible return value in wxMutex::Lock");
 133     }
 134
 135     m_locked++;
 136     return wxMUTEX_NO_ERROR;
 137 }
 138
 139 wxMutexError wxMutex::TryLock()
 140 {
 141     DWORD ret;
 142
 143     ret = WaitForSingleObject(p_internal->p_mutex, 0);
 144     if (ret == WAIT_TIMEOUT || ret == WAIT_ABANDONED)
 145         return wxMUTEX_BUSY;
 146
 147     m_locked++;
 148     return wxMUTEX_NO_ERROR;
 149 }
 150
 151 wxMutexError wxMutex::Unlock()
 152 {
 153     if (m_locked > 0)
 154         m_locked--;
 155
 156     BOOL ret = ReleaseMutex(p_internal->p_mutex);
 157     if ( ret == 0 )
 158     {
 159         wxLogSysError(_("Couldn't release a mutex"));
 160         return wxMUTEX_MISC_ERROR;
 161     }
 162
 163     return wxMUTEX_NO_ERROR;
 164 }
 165
 166 // ----------------------------------------------------------------------------
 167 // wxCondition implementation
 168 // ----------------------------------------------------------------------------
 169
 170 class wxConditionInternal
 171 {
 172 public:
 173     HANDLE event;
 174     int waiters;
 175 };
 176
 177 wxCondition::wxCondition()
 178 {
 179     p_internal = new wxConditionInternal;
 180     p_internal->event = CreateEvent(NULL, FALSE, FALSE, NULL);
 181     if ( !p_internal->event )
 182     {
 183         wxLogSysError(_("Can not create event object."));
 184     }
 185
 186     p_internal->waiters = 0;
 187 }
 188
 189 wxCondition::~wxCondition()
 190 {
 191     CloseHandle(p_internal->event);
 192 }
 193
 194 void wxCondition::Wait(wxMutex& mutex)
 195 {
 196     mutex.Unlock();
 197     p_internal->waiters++;
 198     WaitForSingleObject(p_internal->event, INFINITE);
 199     p_internal->waiters--;
 200     mutex.Lock();
 201 }
 202
 203 bool wxCondition::Wait(wxMutex& mutex,
 204                        unsigned long sec,
 205                        unsigned long nsec)
 206 {
 207     DWORD ret;
 208
 209     mutex.Unlock();
 210     p_internal->waiters++;
 211     ret = WaitForSingleObject(p_internal->event, (sec*1000)+(nsec/1000000));
 212     p_internal->waiters--;
 213     mutex.Lock();
 214
 215     return (ret != WAIT_TIMEOUT);
 216 }
 217
 218 void wxCondition::Signal()
 219 {
 220     SetEvent(p_internal->event);
 221 }
 222
 223 void wxCondition::Broadcast()
 224 {
 225     int i;
 226
 227     for (i=0;i<p_internal->waiters;i++)
 228     {
 229         if ( SetEvent(p_internal->event) == 0 )
 230         {
 231             wxLogSysError(_("Couldn't change the state of event object."));
 232         }
 233     }
 234 }
 235
 236 // ----------------------------------------------------------------------------
 237 // wxCriticalSection implementation
 238 // ----------------------------------------------------------------------------
 239
 240 class wxCriticalSectionInternal
 241 {
 242 public:
 243     // init the critical section object
 244     wxCriticalSectionInternal()
 245         { ::InitializeCriticalSection(&m_data); }
 246
 247     // implicit cast to the associated data
 248     operator CRITICAL_SECTION *() { return &m_data; }
 249
 250     // free the associated ressources
 251     ~wxCriticalSectionInternal()
 252         { ::DeleteCriticalSection(&m_data); }
 253
 254 private:
 255     CRITICAL_SECTION m_data;
 256 };
 257
 258 wxCriticalSection::wxCriticalSection()
 259 {
 260     m_critsect = new wxCriticalSectionInternal;
 261 }
 262
 263 wxCriticalSection::~wxCriticalSection()
 264 {
 265     delete m_critsect;
 266 }
 267
 268 void wxCriticalSection::Enter()
 269 {
 270     ::EnterCriticalSection(*m_critsect);
 271 }
 272
 273 void wxCriticalSection::Leave()
 274 {
 275     ::LeaveCriticalSection(*m_critsect);
 276 }
 277
 278 // ----------------------------------------------------------------------------
 279 // wxThread implementation
 280 // ----------------------------------------------------------------------------
 281
 282 // wxThreadInternal class
 283 // ----------------------
 284
 285 class wxThreadInternal
 286 {
 287 public:
 288     wxThreadInternal()
 289     {
 290         m_hThread = 0;
 291         m_state = STATE_NEW;
 292         m_priority = WXTHREAD_DEFAULT_PRIORITY;
 293     }
 294
 295     // create a new (suspended) thread (for the given thread object)
 296     bool Create(wxThread *thread);
 297
 298     // suspend/resume/terminate
 299     bool Suspend();
 300     bool Resume();
 301     void Cancel() { m_state = STATE_CANCELED; }
 302
 303     // thread state
 304     void SetState(wxThreadState state) { m_state = state; }
 305     wxThreadState GetState() const { return m_state; }
 306
 307     // thread priority
 308     void SetPriority(unsigned int priority) { m_priority = priority; }
 309     unsigned int GetPriority() const { return m_priority; }
 310
 311     // thread handle and id
 312     HANDLE GetHandle() const { return m_hThread; }
 313     DWORD  GetId() const { return m_tid; }
 314
 315     // thread function
 316     static DWORD WinThreadStart(wxThread *thread);
 317
 318 private:
 319     HANDLE        m_hThread;    // handle of the thread
 320     wxThreadState m_state;      // state, see wxThreadState enum
 321     unsigned int  m_priority;   // thread priority in "wx" units
 322     DWORD         m_tid;        // thread id
 323 };
 324
 325 DWORD wxThreadInternal::WinThreadStart(wxThread *thread)
 326 {
 327     // store the thread object in the TLS
 328     if ( !::TlsSetValue(s_tlsThisThread, thread) )
 329     {
 330         wxLogSysError(_("Can not start thread: error writing TLS."));
 331
 332         return (DWORD)-1;
 333     }
 334
 335     DWORD ret = (DWORD)thread->Entry();
 336     thread->p_internal->SetState(STATE_EXITED);
 337     thread->OnExit();
 338
 339     delete thread;
 340
 341     return ret;
 342 }
 343
 344 bool wxThreadInternal::Create(wxThread *thread)
 345 {
 346     m_hThread = ::CreateThread
 347                   (
 348                     NULL,                               // default security
 349                     0,                                  // default stack size
 350                     (LPTHREAD_START_ROUTINE)            // thread entry point
 351                     wxThreadInternal::WinThreadStart,   //
 352                     (LPVOID)thread,                     // parameter
 353                     CREATE_SUSPENDED,                   // flags
 354                     &m_tid                              // [out] thread id
 355                   );
 356
 357     if ( m_hThread == NULL )
 358     {
 359         wxLogSysError(_("Can't create thread"));
 360
 361         return FALSE;
 362     }
 363
 364     // translate wxWindows priority to the Windows one
 365     int win_priority;
 366     if (m_priority <= 20)
 367         win_priority = THREAD_PRIORITY_LOWEST;
 368     else if (m_priority <= 40)
 369         win_priority = THREAD_PRIORITY_BELOW_NORMAL;
 370     else if (m_priority <= 60)
 371         win_priority = THREAD_PRIORITY_NORMAL;
 372     else if (m_priority <= 80)
 373         win_priority = THREAD_PRIORITY_ABOVE_NORMAL;
 374     else if (m_priority <= 100)
 375         win_priority = THREAD_PRIORITY_HIGHEST;
 376     else
 377     {
 378         wxFAIL_MSG("invalid value of thread priority parameter");
 379         win_priority = THREAD_PRIORITY_NORMAL;
 380     }
 381
 382     if ( ::SetThreadPriority(m_hThread, win_priority) == 0 )
 383     {
 384         wxLogSysError(_("Can't set thread priority"));
 385     }
 386
 387     return TRUE;
 388 }
 389
 390 bool wxThreadInternal::Suspend()
 391 {
 392     DWORD nSuspendCount = ::SuspendThread(m_hThread);
 393     if ( nSuspendCount == (DWORD)-1 )
 394     {
 395         wxLogSysError(_("Can not suspend thread %x"), m_hThread);
 396
 397         return FALSE;
 398     }
 399
 400     m_state = STATE_PAUSED;
 401
 402     return TRUE;
 403 }
 404
 405 bool wxThreadInternal::Resume()
 406 {
 407     DWORD nSuspendCount = ::ResumeThread(m_hThread);
 408     if ( nSuspendCount == (DWORD)-1 )
 409     {
 410         wxLogSysError(_("Can not resume thread %x"), m_hThread);
 411
 412         return FALSE;
 413     }
 414
 415     m_state = STATE_RUNNING;
 416
 417     return TRUE;
 418 }
 419
 420 // static functions
 421 // ----------------
 422
 423 wxThread *wxThread::This()
 424 {
 425     wxThread *thread = (wxThread *)::TlsGetValue(s_tlsThisThread);
 426
 427     // be careful, 0 may be a valid return value as well
 428     if ( !thread && (::GetLastError() != NO_ERROR) )
 429     {
 430         wxLogSysError(_("Couldn't get the current thread pointer"));
 431
 432         // return NULL...
 433     }
 434
 435     return thread;
 436 }
 437
 438 bool wxThread::IsMain()
 439 {
 440     return ::GetCurrentThreadId() == s_idMainThread;
 441 }
 442
 443 void wxThread::Yield()
 444 {
 445     // 0 argument to Sleep() is special
 446     ::Sleep(0);
 447 }
 448
 449 void wxThread::Sleep(unsigned long milliseconds)
 450 {
 451     ::Sleep(milliseconds);
 452 }
 453
 454 // create/start thread
 455 // -------------------
 456
 457 wxThreadError wxThread::Create()
 458 {
 459     if ( !p_internal->Create(this) )
 460         return wxTHREAD_NO_RESOURCE;
 461
 462     return wxTHREAD_NO_ERROR;
 463 }
 464
 465 wxThreadError wxThread::Run()
 466 {
 467     wxCriticalSectionLocker lock(m_critsect);
 468
 469     if ( p_internal->GetState() != STATE_NEW )
 470     {
 471         // actually, it may be almost any state at all, not only STATE_RUNNING
 472         return wxTHREAD_RUNNING;
 473     }
 474
 475     return Resume();
 476 }
 477
 478 // suspend/resume thread
 479 // ---------------------
 480
 481 wxThreadError wxThread::Pause()
 482 {
 483     wxCriticalSectionLocker lock(m_critsect);
 484
 485     return p_internal->Suspend() ? wxTHREAD_NO_ERROR : wxTHREAD_MISC_ERROR;
 486 }
 487
 488 wxThreadError wxThread::Resume()
 489 {
 490     wxCriticalSectionLocker lock(m_critsect);
 491
 492     return p_internal->Resume() ? wxTHREAD_NO_ERROR : wxTHREAD_MISC_ERROR;
 493 }
 494
 495 // stopping thread
 496 // ---------------
 497
 498 wxThread::ExitCode wxThread::Delete()
 499 {
 500     ExitCode rc = 0;
 501
 502     // Delete() is always safe to call, so consider all possible states
 503     if ( IsPaused() )
 504         Resume();
 505
 506     if ( IsRunning() )
 507     {
 508         if ( IsMain() )
 509         {
 510             // set flag for wxIsWaitingForThread()
 511             s_waitingForThread = TRUE;
 512
 513             wxBeginBusyCursor();
 514         }
 515
 516         HANDLE hThread;
 517         {
 518             wxCriticalSectionLocker lock(m_critsect);
 519
 520             p_internal->Cancel();
 521             hThread = p_internal->GetHandle();
 522         }
 523
 524         // we can't just wait for the thread to terminate because it might be
 525         // calling some GUI functions and so it will never terminate before we
 526         // process the Windows messages that result from these functions
 527         DWORD result;
 528         do
 529         {
 530             result = ::MsgWaitForMultipleObjects
 531                      (
 532                        1,              // number of objects to wait for
 533                        &hThread,       // the objects
 534                        FALSE,          // don't wait for all objects
 535                        INFINITE,       // no timeout
 536                        QS_ALLEVENTS    // return as soon as there are any events
 537                      );
 538
 539             switch ( result )
 540             {
 541                 case 0xFFFFFFFF:
 542                     // error
 543                     wxLogSysError(_("Can not wait for thread termination"));
 544                     Kill();
 545                     return (ExitCode)-1;
 546
 547                 case WAIT_OBJECT_0:
 548                     // thread we're waiting for terminated
 549                     break;
 550
 551                 case WAIT_OBJECT_0 + 1:
 552                     // new message arrived, process it
 553                     if ( !wxTheApp->DoMessage() )
 554                     {
 555                         // WM_QUIT received: kill the thread
 556                         Kill();
 557
 558                         return (ExitCode)-1;
 559                     }
 560
 561                     if ( IsMain() )
 562                     {
 563                         // give the thread we're waiting for chance to exit
 564                         // from the GUI call it might have been in
 565                         if ( (s_nWaitingForGui > 0) && wxGuiOwnedByMainThread() )
 566                         {
 567                             wxMutexGuiLeave();
 568                         }
 569                     }
 570
 571                     break;
 572
 573                 default:
 574                     wxFAIL_MSG("unexpected result of MsgWaitForMultipleObject");
 575             }
 576         } while ( result != WAIT_OBJECT_0 );
 577
 578         if ( IsMain() )
 579         {
 580             s_waitingForThread = FALSE;
 581
 582             wxEndBusyCursor();
 583         }
 584
 585         if ( !::GetExitCodeThread(hThread, (LPDWORD)&rc) )
 586         {
 587             wxLogLastError("GetExitCodeThread");
 588
 589             rc = (ExitCode)-1;
 590         }
 591
 592         wxASSERT_MSG( (LPVOID)rc != (LPVOID)STILL_ACTIVE,
 593                       "thread must be already terminated." );
 594
 595         ::CloseHandle(hThread);
 596     }
 597
 598     return rc;
 599 }
 600
 601 wxThreadError wxThread::Kill()
 602 {
 603     if ( !IsRunning() )
 604         return wxTHREAD_NOT_RUNNING;
 605
 606     if ( !::TerminateThread(p_internal->GetHandle(), (DWORD)-1) )
 607     {
 608         wxLogSysError(_("Couldn't terminate thread"));
 609
 610         return wxTHREAD_MISC_ERROR;
 611     }
 612
 613     delete this;
 614
 615     return wxTHREAD_NO_ERROR;
 616 }
 617
 618 void wxThread::Exit(void *status)
 619 {
 620     delete this;
 621
 622     ::ExitThread((DWORD)status);
 623
 624     wxFAIL_MSG("Couldn't return from ExitThread()!");
 625 }
 626
 627 void wxThread::SetPriority(unsigned int prio)
 628 {
 629     wxCriticalSectionLocker lock(m_critsect);
 630
 631     p_internal->SetPriority(prio);
 632 }
 633
 634 unsigned int wxThread::GetPriority() const
 635 {
 636     wxCriticalSectionLocker lock((wxCriticalSection &)m_critsect);
 637
 638     return p_internal->GetPriority();
 639 }
 640
 641 unsigned long wxThread::GetID() const
 642 {
 643     wxCriticalSectionLocker lock((wxCriticalSection &)m_critsect);
 644
 645     return (unsigned long)p_internal->GetId();
 646 }
 647
 648 bool wxThread::IsRunning() const
 649 {
 650     wxCriticalSectionLocker lock((wxCriticalSection &)m_critsect);
 651
 652     return p_internal->GetState() == STATE_RUNNING;
 653 }
 654
 655 bool wxThread::IsAlive() const
 656 {
 657     wxCriticalSectionLocker lock((wxCriticalSection &)m_critsect);
 658
 659     return (p_internal->GetState() == STATE_RUNNING) ||
 660            (p_internal->GetState() == STATE_PAUSED);
 661 }
 662
 663 bool wxThread::TestDestroy()
 664 {
 665     wxCriticalSectionLocker lock((wxCriticalSection &)m_critsect);
 666
 667     return p_internal->GetState() == STATE_CANCELED;
 668 }
 669
 670 wxThread::wxThread()
 671 {
 672     p_internal = new wxThreadInternal();
 673 }
 674
 675 wxThread::~wxThread()
 676 {
 677     delete p_internal;
 678 }
 679
 680 // ----------------------------------------------------------------------------
 681 // Automatic initialization for thread module
 682 // ----------------------------------------------------------------------------
 683
 684 class wxThreadModule : public wxModule
 685 {
 686 public:
 687     virtual bool OnInit();
 688     virtual void OnExit();
 689
 690 private:
 691     DECLARE_DYNAMIC_CLASS(wxThreadModule)
 692 };
 693
 694 IMPLEMENT_DYNAMIC_CLASS(wxThreadModule, wxModule)
 695
 696 bool wxThreadModule::OnInit()
 697 {
 698     // allocate TLS index for storing the pointer to the current thread
 699     s_tlsThisThread = ::TlsAlloc();
 700     if ( s_tlsThisThread == 0xFFFFFFFF )
 701     {
 702         // in normal circumstances it will only happen if all other
 703         // TLS_MINIMUM_AVAILABLE (>= 64) indices are already taken - in other
 704         // words, this should never happen
 705         wxLogSysError(_("Thread module initialization failed: "
 706                         "impossible to allocate index in thread "
 707                         "local storage"));
 708
 709         return FALSE;
 710     }
 711
 712     // main thread doesn't have associated wxThread object, so store 0 in the
 713     // TLS instead
 714     if ( !::TlsSetValue(s_tlsThisThread, (LPVOID)0) )
 715     {
 716         ::TlsFree(s_tlsThisThread);
 717         s_tlsThisThread = 0xFFFFFFFF;
 718
 719         wxLogSysError(_("Thread module initialization failed: "
 720                         "can not store value in thread local storage"));
 721
 722         return FALSE;
 723     }
 724
 725     s_critsectWaitingForGui = new wxCriticalSection();
 726
 727     s_critsectGui = new wxCriticalSection();
 728     s_critsectGui->Enter();
 729
 730     // no error return for GetCurrentThreadId()
 731     s_idMainThread = ::GetCurrentThreadId();
 732
 733     return TRUE;
 734 }
 735
 736 void wxThreadModule::OnExit()
 737 {
 738     if ( !::TlsFree(s_tlsThisThread) )
 739     {
 740         wxLogLastError("TlsFree failed.");
 741     }
 742
 743     if ( s_critsectGui )
 744     {
 745         s_critsectGui->Leave();
 746         delete s_critsectGui;
 747         s_critsectGui = NULL;
 748     }
 749
 750     wxDELETE(s_critsectWaitingForGui);
 751 }
 752
 753 // ----------------------------------------------------------------------------
 754 // under Windows, these functions are implemented usign a critical section and
 755 // not a mutex, so the names are a bit confusing
 756 // ----------------------------------------------------------------------------
 757
 758 void WXDLLEXPORT wxMutexGuiEnter()
 759 {
 760     // this would dead lock everything...
 761     wxASSERT_MSG( !wxThread::IsMain(),
 762                   "main thread doesn't want to block in wxMutexGuiEnter()!" );
 763
 764     // the order in which we enter the critical sections here is crucial!!
 765
 766     // set the flag telling to the main thread that we want to do some GUI
 767     {
 768         wxCriticalSectionLocker enter(*s_critsectWaitingForGui);
 769
 770         s_nWaitingForGui++;
 771     }
 772
 773     wxWakeUpMainThread();
 774
 775     // now we may block here because the main thread will soon let us in
 776     // (during the next iteration of OnIdle())
 777     s_critsectGui->Enter();
 778 }
 779
 780 void WXDLLEXPORT wxMutexGuiLeave()
 781 {
 782     wxCriticalSectionLocker enter(*s_critsectWaitingForGui);
 783
 784     if ( wxThread::IsMain() )
 785     {
 786         s_bGuiOwnedByMainThread = FALSE;
 787     }
 788     else
 789     {
 790         // decrement the number of waiters now
 791         wxASSERT_MSG( s_nWaitingForGui > 0,
 792                       "calling wxMutexGuiLeave() without entering it first?" );
 793
 794         s_nWaitingForGui--;
 795
 796         wxWakeUpMainThread();
 797     }
 798
 799     s_critsectGui->Leave();
 800 }
 801
 802 void WXDLLEXPORT wxMutexGuiLeaveOrEnter()
 803 {
 804     wxASSERT_MSG( wxThread::IsMain(),
 805                   "only main thread may call wxMutexGuiLeaveOrEnter()!" );
 806
 807     wxCriticalSectionLocker enter(*s_critsectWaitingForGui);
 808
 809     if ( s_nWaitingForGui == 0 )
 810     {
 811         // no threads are waiting for GUI - so we may acquire the lock without
 812         // any danger (but only if we don't already have it)
 813         if ( !wxGuiOwnedByMainThread() )
 814         {
 815             s_critsectGui->Enter();
 816
 817             s_bGuiOwnedByMainThread = TRUE;
 818         }
 819         //else: already have it, nothing to do
 820     }
 821     else
 822     {
 823         // some threads are waiting, release the GUI lock if we have it
 824         if ( wxGuiOwnedByMainThread() )
 825         {
 826             wxMutexGuiLeave();
 827         }
 828         //else: some other worker thread is doing GUI
 829     }
 830 }
 831
 832 bool WXDLLEXPORT wxGuiOwnedByMainThread()
 833 {
 834     return s_bGuiOwnedByMainThread;
 835 }
 836
 837 // wake up the main thread if it's in ::GetMessage()
 838 void WXDLLEXPORT wxWakeUpMainThread()
 839 {
 840     // sending any message would do - hopefully WM_NULL is harmless enough
 841     if ( !::PostThreadMessage(s_idMainThread, WM_NULL, 0, 0) )
 842     {
 843         // should never happen
 844         wxLogLastError("PostThreadMessage(WM_NULL)");
 845     }
 846 }
 847
 848 bool WXDLLEXPORT wxIsWaitingForThread()
 849 {
 850     return s_waitingForThread;
 851 }
 852
 853 #endif // wxUSE_THREADS