1 /////////////////////////////////////////////////////////////////////////////
3 // Purpose: interface of all thread-related wxWidgets classes
4 // Author: wxWidgets team
6 // Licence: wxWindows license
7 /////////////////////////////////////////////////////////////////////////////
10 /** See wxCondition. */
15 wxCOND_TIMEOUT
, //!< WaitTimeout() has timed out
23 wxCondition variables correspond to pthread conditions or to Win32 event objects.
24 They may be used in a multithreaded application to wait until the given condition
25 becomes @true which happens when the condition becomes signaled.
27 For example, if a worker thread is doing some long task and another thread has
28 to wait until it is finished, the latter thread will wait on the condition
29 object and the worker thread will signal it on exit (this example is not
30 perfect because in this particular case it would be much better to just
31 wxThread::Wait for the worker thread, but if there are several worker threads
32 it already makes much more sense).
34 Note that a call to wxCondition::Signal may happen before the other thread calls
35 wxCondition::Wait and, just as with the pthread conditions, the signal is then
36 lost and so if you want to be sure that you don't miss it you must keep the
37 mutex associated with the condition initially locked and lock it again before calling
38 wxCondition::Signal. Of course, this means that this call is going to block
39 until wxCondition::Wait is called by another thread.
41 @section condition_example Example
43 This example shows how a main thread may launch a worker thread which starts
44 running and then waits until the main thread signals it to continue:
47 class MySignallingThread : public wxThread
50 MySignallingThread(wxMutex *mutex, wxCondition *condition)
53 m_condition = condition;
58 virtual ExitCode Entry()
62 // tell the other(s) thread(s) that we're about to terminate: we must
63 // lock the mutex first or we might signal the condition before the
64 // waiting threads start waiting on it!
65 wxMutexLocker lock(*m_mutex);
66 m_condition->Broadcast(); // same as Signal() here -- one waiter only
72 wxCondition *m_condition;
79 wxCondition condition(mutex);
81 // the mutex should be initially locked
84 // create and run the thread but notice that it won't be able to
85 // exit (and signal its exit) before we unlock the mutex below
86 MySignallingThread *thread = new MySignallingThread(&mutex, &condition);
90 // wait for the thread termination: Wait() atomically unlocks the mutex
91 // which allows the thread to continue and starts waiting
99 Of course, here it would be much better to simply use a joinable thread and
100 call wxThread::Wait on it, but this example does illustrate the importance of
101 properly locking the mutex when using wxCondition.
106 @see wxThread, wxMutex
112 Default and only constructor.
113 The @a mutex must be locked by the caller before calling Wait() function.
114 Use IsOk() to check if the object was successfully initialized.
116 wxCondition(wxMutex
& mutex
);
119 Destroys the wxCondition object.
121 The destructor is not virtual so this class should not be used polymorphically.
126 Broadcasts to all waiting threads, waking all of them up.
128 Note that this method may be called whether the mutex associated with
129 this condition is locked or not.
133 wxCondError
Broadcast();
136 Returns @true if the object had been initialized successfully, @false
137 if an error occurred.
142 Signals the object waking up at most one thread.
144 If several threads are waiting on the same condition, the exact thread
145 which is woken up is undefined. If no threads are waiting, the signal is
146 lost and the condition would have to be signalled again to wake up any
147 thread which may start waiting on it later.
149 Note that this method may be called whether the mutex associated with this
150 condition is locked or not.
154 wxCondError
Signal();
157 Waits until the condition is signalled.
159 This method atomically releases the lock on the mutex associated with this
160 condition (this is why it must be locked prior to calling Wait()) and puts the
161 thread to sleep until Signal() or Broadcast() is called.
162 It then locks the mutex again and returns.
164 Note that even if Signal() had been called before Wait() without waking
165 up any thread, the thread would still wait for another one and so it is
166 important to ensure that the condition will be signalled after
167 Wait() or the thread may sleep forever.
169 @return Returns wxCOND_NO_ERROR on success, another value if an error occurred.
176 Waits until the condition is signalled or the timeout has elapsed.
178 This method is identical to Wait() except that it returns, with the
179 return code of @c wxCOND_TIMEOUT as soon as the given timeout expires.
182 Timeout in milliseconds
184 @return Returns wxCOND_NO_ERROR if the condition was signalled,
185 wxCOND_TIMEOUT if the timeout elapsed before this happened or
186 another error code from wxCondError enum.
188 wxCondError
WaitTimeout(unsigned long milliseconds
);
193 @class wxCriticalSectionLocker
195 This is a small helper class to be used with wxCriticalSection objects.
197 A wxCriticalSectionLocker enters the critical section in the constructor and
198 leaves it in the destructor making it much more difficult to forget to leave
199 a critical section (which, in general, will lead to serious and difficult
207 // gs_critSect is some (global) critical section guarding access to the
209 wxCriticalSectionLocker locker(gs_critSect);
226 Without wxCriticalSectionLocker, you would need to remember to manually leave
227 the critical section before each @c return.
232 @see wxCriticalSection, wxMutexLocker
234 class wxCriticalSectionLocker
238 Constructs a wxCriticalSectionLocker object associated with given
239 @a criticalsection and enters it.
241 wxCriticalSectionLocker(wxCriticalSection
& criticalsection
);
244 Destructor leaves the critical section.
246 ~wxCriticalSectionLocker();
252 @class wxThreadHelper
254 The wxThreadHelper class is a mix-in class that manages a single background
255 thread, either detached or joinable (see wxThread for the differences).
256 By deriving from wxThreadHelper, a class can implement the thread
257 code in its own wxThreadHelper::Entry() method and easily share data and
258 synchronization objects between the main thread and the worker thread.
260 Doing this prevents the awkward passing of pointers that is needed when the
261 original object in the main thread needs to synchronize with its worker thread
262 in its own wxThread derived object.
264 For example, wxFrame may need to make some calculations in a background thread
265 and then display the results of those calculations in the main window.
267 Ordinarily, a wxThread derived object would be created with the calculation
268 code implemented in wxThread::Entry. To access the inputs to the calculation,
269 the frame object would often need to pass a pointer to itself to the thread object.
270 Similarly, the frame object would hold a pointer to the thread object.
272 Shared data and synchronization objects could be stored in either object
273 though the object without the data would have to access the data through
275 However with wxThreadHelper the frame object and the thread object are
276 treated as the same object. Shared data and synchronization variables are
277 stored in the single object, eliminating a layer of indirection and the
282 extern const wxEventType wxEVT_COMMAND_MYTHREAD_UPDATE;
284 class MyFrame : public wxFrame, public wxThreadHelper
290 // it's better to do any thread cleanup in the OnClose()
291 // event handler, rather than in the destructor.
292 // This is because the event loop for a top-level window is not
293 // active anymore when its destructor is called and if the thread
294 // sends events when ending, they won't be processed unless
295 // you ended the thread from OnClose.
296 // See @ref overview_windowdeletion for more info.
300 void DoStartALongTask();
301 void OnThreadUpdate(wxCommandEvent& evt);
302 void OnClose(wxCloseEvent& evt);
306 virtual wxThread::ExitCode Entry();
308 // the output data of the Entry() routine:
310 wxCriticalSection m_dataCS; // protects field above
312 DECLARE_EVENT_TABLE()
315 DEFINE_EVENT_TYPE(wxEVT_COMMAND_MYTHREAD_UPDATE)
316 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
317 EVT_COMMAND(wxID_ANY, wxEVT_COMMAND_MYTHREAD_UPDATE, MyFrame::OnThreadUpdate)
318 EVT_CLOSE(MyFrame::OnClose)
321 void MyFrame::DoStartALongTask()
323 // we want to start a long task, but we don't want our GUI to block
324 // while it's executed, so we use a thread to do it.
325 if (CreateThread(wxTHREAD_JOINABLE) != wxTHREAD_NO_ERROR)
327 wxLogError("Could not create the worker thread!");
332 if (GetThread()->Run() != wxTHREAD_NO_ERROR)
334 wxLogError("Could not run the worker thread!");
339 wxThread::ExitCode MyFrame::Entry()
342 // this function gets executed in the secondary thread context!
346 // here we do our long task, periodically calling TestDestroy():
347 while (!GetThread()->TestDestroy())
349 // since this Entry() is implemented in MyFrame context we don't
350 // need any pointer to access the m_data, m_processedData, m_dataCS
351 // variables... very nice!
353 // this is an example of the generic structure of a download thread:
355 download_chunk(buffer, 1024); // this takes time...
358 // ensure noone reads m_data while we write it
359 wxCriticalSectionLocker lock(m_dataCS);
360 memcpy(m_data+offset, buffer, 1024);
365 // VERY IMPORTANT: do not call any GUI function inside this
366 // function; rather use wxQueueEvent():
367 wxQueueEvent(this, new wxCommandEvent(wxEVT_COMMAND_MYTHREAD_UPDATE));
368 // we used pointer 'this' assuming it's safe; see OnClose()
371 // TestDestroy() returned true (which means the main thread asked us
372 // to terminate as soon as possible) or we ended the long task...
373 return (wxThread::ExitCode)0;
376 void MyFrame::OnClose(wxCloseEvent&)
378 // important: before terminating, we _must_ wait for our joinable
379 // thread to end, if it's running; in fact it uses variables of this
380 // instance and posts events to *this event handler
382 if (GetThread() && // DoStartALongTask() may have not been called
383 GetThread()->IsRunning())
389 void MyFrame::OnThreadUpdate(wxCommandEvent&evt)
391 // ...do something... e.g. m_pGauge->Pulse();
393 // read some parts of m_data just for fun:
394 wxCriticalSectionLocker lock(m_dataCS);
395 wxPrintf("%c", m_data[100]);
408 This constructor simply initializes internal member variables and tells
409 wxThreadHelper which type the thread internally managed should be.
411 wxThreadHelper(wxThreadKind kind
= wxTHREAD_JOINABLE
);
414 The destructor frees the resources associated with the thread, forcing
415 it to terminate (it uses wxThread::Kill function).
417 Because of the wxThread::Kill unsafety, you should always wait
418 (with wxThread::Wait) for joinable threads to end or call wxThread::Delete
419 on detached threads, instead of relying on this destructor for stopping
422 virtual ~wxThreadHelper();
425 This is the entry point of the thread.
427 This function is pure virtual and must be implemented by any derived class.
428 The thread execution will start here.
430 You'll typically want your Entry() to look like:
432 wxThread::ExitCode Entry()
434 while (!GetThread()->TestDestroy())
436 // ... do some work ...
441 if (HappenedStoppingError)
442 return (wxThread::ExitCode)1; // failure
445 return (wxThread::ExitCode)0; // success
449 The returned value is the thread exit code which is only useful for
450 joinable threads and is the value returned by @c "GetThread()->Wait()".
452 This function is called by wxWidgets itself and should never be called
455 virtual ExitCode
Entry() = 0;
458 Creates a new thread of the given @a kind.
460 The thread object is created in the suspended state, and you
461 should call @ref wxThread::Run "GetThread()->Run()" to start running it.
463 You may optionally specify the stack size to be allocated to it (ignored
464 on platforms that don't support setting it explicitly, e.g. Unix).
466 @return One of the ::wxThreadError enum values.
468 wxThreadError
CreateThread(wxThreadKind kind
= wxTHREAD_JOINABLE
,
469 unsigned int stackSize
= 0);
472 This is a public function that returns the wxThread object associated with
475 wxThread
* GetThread() const;
478 Returns the last type of thread given to the CreateThread() function
479 or to the constructor.
481 wxThreadKind
GetThreadKind() const;
485 Possible critical section types
488 enum wxCriticalSectionType
491 /** Recursive critical section under both Windows and Unix */
493 wxCRITSEC_NON_RECURSIVE
494 /** Non-recursive critical section under Unix, recursive under Windows */
498 @class wxCriticalSection
500 A critical section object is used for exactly the same purpose as a wxMutex.
501 The only difference is that under Windows platform critical sections are only
502 visible inside one process, while mutexes may be shared among processes,
503 so using critical sections is slightly more efficient.
505 The terminology is also slightly different: mutex may be locked (or acquired)
506 and unlocked (or released) while critical section is entered and left by the program.
508 Finally, you should try to use wxCriticalSectionLocker class whenever
509 possible instead of directly using wxCriticalSection for the same reasons
510 wxMutexLocker is preferrable to wxMutex - please see wxMutex for an example.
515 @see wxThread, wxCondition, wxCriticalSectionLocker
517 class wxCriticalSection
521 Default constructor initializes critical section object.
522 By default critical sections are recursive under Unix and Windows.
524 wxCriticalSection( wxCriticalSectionType critSecType
= wxCRITSEC_DEFAULT
);
527 Destructor frees the resources.
529 ~wxCriticalSection();
532 Enter the critical section (same as locking a mutex).
534 There is no error return for this function.
535 After entering the critical section protecting some global
536 data the thread running in critical section may safely use/modify it.
541 Leave the critical section allowing other threads use the global data
542 protected by it. There is no error return for this function.
548 The possible thread kinds.
552 /** Detached thread */
555 /** Joinable thread */
560 The possible thread errors.
565 wxTHREAD_NO_ERROR
= 0,
567 /** No resource left to create a new thread. */
568 wxTHREAD_NO_RESOURCE
,
570 /** The thread is already running. */
573 /** The thread isn't running. */
574 wxTHREAD_NOT_RUNNING
,
576 /** Thread we waited for had to be killed. */
579 /** Some other error */
584 Defines the interval of priority
588 WXTHREAD_MIN_PRIORITY
= 0u,
589 WXTHREAD_DEFAULT_PRIORITY
= 50u,
590 WXTHREAD_MAX_PRIORITY
= 100u
597 A thread is basically a path of execution through a program.
598 Threads are sometimes called @e light-weight processes, but the fundamental difference
599 between threads and processes is that memory spaces of different processes are
600 separated while all threads share the same address space.
602 While it makes it much easier to share common data between several threads, it
603 also makes it much easier to shoot oneself in the foot, so careful use of
604 synchronization objects such as mutexes (see wxMutex) or critical sections
605 (see wxCriticalSection) is recommended.
606 In addition, don't create global thread objects because they allocate memory
607 in their constructor, which will cause problems for the memory checking system.
610 @section thread_types Types of wxThreads
612 There are two types of threads in wxWidgets: @e detached and @e joinable,
613 modeled after the the POSIX thread API. This is different from the Win32 API
614 where all threads are joinable.
616 By default wxThreads in wxWidgets use the @b detached behavior.
617 Detached threads delete themselves once they have completed, either by themselves
618 when they complete processing or through a call to Delete(), and thus
619 @b must be created on the heap (through the new operator, for example).
621 Typically you'll want to store the instances of the detached wxThreads you
622 allocate, so that you can call functions on them.
623 Because of their nature however you'll need to always use a critical section
627 // declare a new type of event, to be used by our MyThread class:
628 extern const wxEventType wxEVT_COMMAND_MYTHREAD_COMPLETED;
629 extern const wxEventType wxEVT_COMMAND_MYTHREAD_UPDATE;
632 class MyThread : public wxThread
635 MyThread(MyFrame *handler)
636 : wxThread(wxTHREAD_DETACHED)
637 { m_pHandler = handler }
641 virtual ExitCode Entry();
645 class MyFrame : public wxFrame
651 // it's better to do any thread cleanup in the OnClose()
652 // event handler, rather than in the destructor.
653 // This is because the event loop for a top-level window is not
654 // active anymore when its destructor is called and if the thread
655 // sends events when ending, they won't be processed unless
656 // you ended the thread from OnClose.
657 // See @ref overview_windowdeletion for more info.
660 void DoStartThread();
661 void DoPauseThread();
663 // a resume routine would be nearly identic to DoPauseThread()
664 void DoResumeThread() { ... }
666 void OnThreadCompletion(wxCommandEvent&);
667 void OnClose(wxCloseEvent&);
671 wxCriticalSection m_pThreadCS; // protects the m_pThread pointer
673 DECLARE_EVENT_TABLE()
676 BEGIN_EVENT_TABLE(MyFrame, wxFrame)
677 EVT_CLOSE(MyFrame::OnClose)
678 EVT_MENU(Minimal_Start, MyFrame::DoStartThread)
679 EVT_COMMAND(wxID_ANY, wxEVT_COMMAND_MYTHREAD_UPDATE, MyFrame::OnThreadUpdate)
680 EVT_COMMAND(wxID_ANY, wxEVT_COMMAND_MYTHREAD_COMPLETED, MyFrame::OnThreadCompletion)
683 DEFINE_EVENT_TYPE(wxEVT_COMMAND_MYTHREAD_COMPLETED)
684 DEFINE_EVENT_TYPE(wxEVT_COMMAND_MYTHREAD_UPDATE)
686 void MyFrame::DoStartThread()
688 m_pThread = new MyThread(this);
690 if ( m_pThread->Create() != wxTHREAD_NO_ERROR )
692 wxLogError("Can't create the thread!");
698 if (m_pThread->Run() != wxTHREAD_NO_ERROR )
700 wxLogError("Can't create the thread!");
705 // after the call to wxThread::Run(), the m_pThread pointer is "unsafe":
706 // at any moment the thread may cease to exist (because it completes its work).
707 // To avoid dangling pointers OnThreadExit() will set m_pThread
708 // to NULL when the thread dies.
712 wxThread::ExitCode MyThread::Entry()
714 while (!TestDestroy())
716 // ... do a bit of work...
718 wxQueueEvent(m_pHandler, new wxCommandEvent(wxEVT_COMMAND_MYTHREAD_UPDATE));
721 // signal the event handler that this thread is going to be destroyed
722 // NOTE: here we assume that using the m_pHandler pointer is safe,
723 // (in this case this is assured by the MyFrame destructor)
724 wxQueueEvent(m_pHandler, new wxCommandEvent(wxEVT_COMMAND_MYTHREAD_COMPLETED));
726 return (wxThread::ExitCode)0; // success
729 MyThread::~MyThread()
731 wxCriticalSectionLocker enter(m_pHandler->m_pThreadCS);
733 // the thread is being destroyed; make sure not to leave dangling pointers around
734 m_pHandler->m_pThread = NULL;
737 void MyFrame::OnThreadCompletion(wxCommandEvent&)
739 wxMessageOutputDebug().Printf("MYFRAME: MyThread exited!\n");
742 void MyFrame::OnThreadUpdate(wxCommandEvent&)
744 wxMessageOutputDebug().Printf("MYFRAME: MyThread update...\n");
747 void MyFrame::DoPauseThread()
749 // anytime we access the m_pThread pointer we must ensure that it won't
750 // be modified in the meanwhile; since only a single thread may be
751 // inside a given critical section at a given time, the following code
753 wxCriticalSectionLocker enter(m_pThreadCS);
755 if (m_pThread) // does the thread still exist?
757 // without a critical section, once reached this point it may happen
758 // that the OS scheduler gives control to the MyThread::Entry() function,
759 // which in turn may return (because it completes its work) making
760 // invalid the m_pThread pointer
762 if (m_pThread->Pause() != wxTHREAD_NO_ERROR )
763 wxLogError("Can't pause the thread!");
767 void MyFrame::OnClose(wxCloseEvent&)
770 wxCriticalSectionLocker enter(m_pThreadCS);
772 if (m_pThread) // does the thread still exist?
774 m_out.Printf("MYFRAME: deleting thread");
776 if (m_pThread->Delete() != wxTHREAD_NO_ERROR )
777 wxLogError("Can't delete the thread!");
779 } // exit from the critical section to give the thread
780 // the possibility to enter its destructor
781 // (which is guarded with m_pThreadCS critical section!)
785 { // was the ~MyThread() function executed?
786 wxCriticalSectionLocker enter(m_pThreadCS);
787 if (!m_pThread) break;
790 // wait for thread completion
791 wxThread::This()->Sleep(1);
798 For a more detailed and comprehensive example, see @sample{thread}.
799 For a simpler way to share data and synchronization objects between
800 the main and the secondary thread see wxThreadHelper.
802 Conversely, @b joinable threads do not delete themselves when they are done
803 processing and as such are safe to create on the stack. Joinable threads
804 also provide the ability for one to get value it returned from Entry()
806 You shouldn't hurry to create all the threads joinable, however, because this
807 has a disadvantage as well: you @b must Wait() for a joinable thread or the
808 system resources used by it will never be freed, and you also must delete the
809 corresponding wxThread object yourself if you did not create it on the stack.
810 In contrast, detached threads are of the "fire-and-forget" kind: you only have
811 to start a detached thread and it will terminate and destroy itself.
814 @section thread_deletion wxThread Deletion
816 Regardless of whether it has terminated or not, you should call Wait() on a
817 @b joinable thread to release its memory, as outlined in @ref thread_types.
818 If you created a joinable thread on the heap, remember to delete it manually
819 with the @c delete operator or similar means as only detached threads handle
820 this type of memory management.
822 Since @b detached threads delete themselves when they are finished processing,
823 you should take care when calling a routine on one. If you are certain the
824 thread is still running and would like to end it, you may call Delete()
825 to gracefully end it (which implies that the thread will be deleted after
826 that call to Delete()). It should be implied that you should @b never attempt
827 to delete a detached thread with the @c delete operator or similar means.
829 As mentioned, Wait() or Delete() functions attempt to gracefully terminate a
830 joinable and a detached thread, respectively. They do this by waiting until
831 the thread in question calls TestDestroy() or ends processing (i.e. returns
832 from wxThread::Entry).
834 Obviously, if the thread does call TestDestroy() and does not end, the
835 thread which called Wait() or Delete() will come to halt.
836 This is why it's important to call TestDestroy() in the Entry() routine of
837 your threads as often as possible and immediately exit when it returns @true.
839 As a last resort you can end the thread immediately through Kill(). It is
840 strongly recommended that you do not do this, however, as it does not free
841 the resources associated with the object (although the wxThread object of
842 detached threads will still be deleted) and could leave the C runtime
843 library in an undefined state.
846 @section thread_secondary wxWidgets Calls in Secondary Threads
848 All threads other than the "main application thread" (the one running
849 wxApp::OnInit() or the one your main function runs in, for example) are
850 considered "secondary threads". These include all threads created by Create()
851 or the corresponding constructors.
853 GUI calls, such as those to a wxWindow or wxBitmap are explicitly not safe
854 at all in secondary threads and could end your application prematurely.
855 This is due to several reasons, including the underlying native API and
856 the fact that wxThread does not run a GUI event loop similar to other APIs
859 A workaround for some wxWidgets ports is calling wxMutexGUIEnter()
860 before any GUI calls and then calling wxMutexGUILeave() afterwords. However,
861 the recommended way is to simply process the GUI calls in the main thread
862 through an event that is posted by wxQueueEvent().
863 This does not imply that calls to these classes are thread-safe, however,
864 as most wxWidgets classes are not thread-safe, including wxString.
867 @section thread_poll Don't Poll a wxThread
869 A common problem users experience with wxThread is that in their main thread
870 they will check the thread every now and then to see if it has ended through
871 IsRunning(), only to find that their application has run into problems
872 because the thread is using the default behavior (i.e. it's @b detached) and
873 has already deleted itself.
874 Naturally, they instead attempt to use joinable threads in place of the previous
875 behavior. However, polling a wxThread for when it has ended is in general a
876 bad idea - in fact calling a routine on any running wxThread should be avoided
877 if possible. Instead, find a way to notify yourself when the thread has ended.
879 Usually you only need to notify the main thread, in which case you can
880 post an event to it via wxQueueEvent().
881 In the case of secondary threads you can call a routine of another class
882 when the thread is about to complete processing and/or set the value of
883 a variable, possibly using mutexes (see wxMutex) and/or other synchronization
889 @see wxThreadHelper, wxMutex, wxCondition, wxCriticalSection,
896 The return type for the thread functions.
898 typedef void* ExitCode
;
901 This constructor creates a new detached (default) or joinable C++
902 thread object. It does not create or start execution of the real thread -
903 for this you should use the Create() and Run() methods.
905 The possible values for @a kind parameters are:
906 - @b wxTHREAD_DETACHED - Creates a detached thread.
907 - @b wxTHREAD_JOINABLE - Creates a joinable thread.
909 wxThread(wxThreadKind kind
= wxTHREAD_DETACHED
);
912 The destructor frees the resources associated with the thread.
913 Notice that you should never delete a detached thread -- you may only call
914 Delete() on it or wait until it terminates (and auto destructs) itself.
916 Because the detached threads delete themselves, they can only be allocated on the heap.
917 Joinable threads should be deleted explicitly. The Delete() and Kill() functions
918 will not delete the C++ thread object. It is also safe to allocate them on stack.
923 Creates a new thread.
925 The thread object is created in the suspended state, and you should call Run()
926 to start running it. You may optionally specify the stack size to be allocated
927 to it (Ignored on platforms that don't support setting it explicitly,
928 eg. Unix system without @c pthread_attr_setstacksize).
930 If you do not specify the stack size,the system's default value is used.
933 It is a good idea to explicitly specify a value as systems'
934 default values vary from just a couple of KB on some systems (BSD and
935 OS/2 systems) to one or several MB (Windows, Solaris, Linux).
936 So, if you have a thread that requires more than just a few KB of memory, you
937 will have mysterious problems on some platforms but not on the common ones.
938 On the other hand, just indicating a large stack size by default will give you
939 performance issues on those systems with small default stack since those
940 typically use fully committed memory for the stack.
941 On the contrary, if you use a lot of threads (say several hundred),
942 virtual adress space can get tight unless you explicitly specify a
943 smaller amount of thread stack space for each thread.
946 - @b wxTHREAD_NO_ERROR - No error.
947 - @b wxTHREAD_NO_RESOURCE - There were insufficient resources to create the thread.
948 - @b wxTHREAD_NO_RUNNING - The thread is already running
950 wxThreadError
Create(unsigned int stackSize
= 0);
953 Calling Delete() gracefully terminates a @b detached thread, either when
954 the thread calls TestDestroy() or when it finishes processing.
957 This function works on a joinable thread but in that case makes
958 the TestDestroy() function of the thread return @true and then
959 waits for its completion (i.e. it differs from Wait() because
960 it asks the thread to terminate before waiting).
962 See @ref thread_deletion for a broader explanation of this routine.
964 wxThreadError
Delete(void** rc
= NULL
);
967 Returns the number of system CPUs or -1 if the value is unknown.
969 @see SetConcurrency()
971 static int GetCPUCount();
974 Returns the platform specific thread ID of the current thread as a long.
975 This can be used to uniquely identify threads, even if they are not wxThreads.
977 static unsigned long GetCurrentId();
980 Gets the thread identifier: this is a platform dependent number that uniquely
981 identifies the thread throughout the system during its existence
982 (i.e. the thread identifiers may be reused).
984 wxThreadIdType
GetId() const;
987 Gets the priority of the thread, between zero and 100.
989 The following priorities are defined:
990 - @b WXTHREAD_MIN_PRIORITY: 0
991 - @b WXTHREAD_DEFAULT_PRIORITY: 50
992 - @b WXTHREAD_MAX_PRIORITY: 100
994 unsigned int GetPriority() const;
997 Returns @true if the thread is alive (i.e. started and not terminating).
999 Note that this function can only safely be used with joinable threads, not
1000 detached ones as the latter delete themselves and so when the real thread is
1001 no longer alive, it is not possible to call this function because
1002 the wxThread object no longer exists.
1004 bool IsAlive() const;
1007 Returns @true if the thread is of the detached kind, @false if it is a
1010 bool IsDetached() const;
1013 Returns @true if the calling thread is the main application thread.
1015 static bool IsMain();
1018 Returns @true if the thread is paused.
1020 bool IsPaused() const;
1023 Returns @true if the thread is running.
1025 This method may only be safely used for joinable threads, see the remark in
1028 bool IsRunning() const;
1031 Immediately terminates the target thread.
1033 @b "This function is dangerous and should be used with extreme care"
1034 (and not used at all whenever possible)! The resources allocated to the
1035 thread will not be freed and the state of the C runtime library may become
1036 inconsistent. Use Delete() for detached threads or Wait() for joinable
1039 For detached threads Kill() will also delete the associated C++ object.
1040 However this will not happen for joinable threads and this means that you will
1041 still have to delete the wxThread object yourself to avoid memory leaks.
1043 In neither case OnExit() of the dying thread will be called, so no
1044 thread-specific cleanup will be performed.
1045 This function can only be called from another thread context, i.e. a thread
1048 It is also an error to call this function for a thread which is not running or
1049 paused (in the latter case, the thread will be resumed first) -- if you do it,
1050 a @b wxTHREAD_NOT_RUNNING error will be returned.
1052 wxThreadError
Kill();
1055 Called when the thread exits.
1057 This function is called in the context of the thread associated with the
1058 wxThread object, not in the context of the main thread.
1059 This function will not be called if the thread was @ref Kill() killed.
1061 This function should never be called directly.
1063 virtual void OnExit();
1066 Suspends the thread.
1068 Under some implementations (Win32), the thread is suspended immediately,
1069 under others it will only be suspended when it calls TestDestroy() for
1070 the next time (hence, if the thread doesn't call it at all, it won't be
1073 This function can only be called from another thread context.
1075 wxThreadError
Pause();
1078 Resumes a thread suspended by the call to Pause().
1080 This function can only be called from another thread context.
1082 wxThreadError
Resume();
1085 Starts the thread execution. Should be called after Create().
1087 Note that once you Run() a @b detached thread, @e any function call you do
1088 on the thread pointer (you must allocate it on the heap) is @e "unsafe";
1089 i.e. the thread may have terminated at any moment after Run() and your pointer
1090 may be dangling. See @ref thread_types for an example of safe manipulation
1091 of detached threads.
1093 This function can only be called from another thread context.
1095 wxThreadError
Run();
1098 Sets the thread concurrency level for this process.
1100 This is, roughly, the number of threads that the system tries to schedule
1102 The value of 0 for @a level may be used to set the default one.
1104 @return @true on success or @false otherwise (for example, if this function is
1105 not implemented for this platform -- currently everything except Solaris).
1107 static bool SetConcurrency(size_t level
);
1110 Sets the priority of the thread, between 0 and 100.
1111 It can only be set after calling Create() but before calling Run().
1113 The following priorities are defined:
1114 - @b WXTHREAD_MIN_PRIORITY: 0
1115 - @b WXTHREAD_DEFAULT_PRIORITY: 50
1116 - @b WXTHREAD_MAX_PRIORITY: 100
1118 void SetPriority(unsigned int priority
);
1121 Pauses the thread execution for the given amount of time.
1123 This is the same as wxMilliSleep().
1125 static void Sleep(unsigned long milliseconds
);
1128 This function should be called periodically by the thread to ensure that
1129 calls to Pause() and Delete() will work.
1131 If it returns @true, the thread should exit as soon as possible.
1132 Notice that under some platforms (POSIX), implementation of Pause() also
1133 relies on this function being called, so not calling it would prevent
1134 both stopping and suspending thread from working.
1136 virtual bool TestDestroy();
1139 Return the thread object for the calling thread.
1141 @NULL is returned if the calling thread is the main (GUI) thread, but
1142 IsMain() should be used to test whether the thread is really the main one
1143 because @NULL may also be returned for the thread not created with wxThread
1144 class. Generally speaking, the return value for such a thread is undefined.
1146 static wxThread
* This();
1149 Waits for a @b joinable thread to terminate and returns the value the thread
1150 returned from Entry() or @c "(ExitCode)-1" on error. Notice that, unlike
1151 Delete(), this function doesn't cancel the thread in any way so the caller
1152 waits for as long as it takes to the thread to exit.
1154 You can only Wait() for @b joinable (not detached) threads.
1156 This function can only be called from another thread context.
1158 See @ref thread_deletion for a broader explanation of this routine.
1163 Give the rest of the thread's time-slice to the system allowing the other
1166 Note that using this function is @b strongly discouraged, since in
1167 many cases it indicates a design weakness of your threading model
1168 (as does using Sleep() functions).
1170 Threads should use the CPU in an efficient manner, i.e. they should
1171 do their current work efficiently, then as soon as the work is done block
1172 on a wakeup event (wxCondition, wxMutex, select(), poll(), ...) which will
1173 get signalled e.g. by other threads or a user device once further thread
1175 Using Yield() or Sleep() indicates polling-type behaviour, since we're
1176 fuzzily giving up our timeslice and wait until sometime later we'll get
1177 reactivated, at which time we realize that there isn't really much to do
1178 and Yield() again...
1180 The most critical characteristic of Yield() is that it's operating system
1181 specific: there may be scheduler changes which cause your thread to not
1182 wake up relatively soon again, but instead many seconds later,
1183 causing huge performance issues for your application.
1186 With a well-behaving, CPU-efficient thread the operating system is likely
1187 to properly care for its reactivation the moment it needs it, whereas with
1188 non-deterministic, Yield-using threads all bets are off and the system
1189 scheduler is free to penalize them drastically</strong>, and this effect
1190 gets worse with increasing system load due to less free CPU resources available.
1191 You may refer to various Linux kernel @c sched_yield discussions for more
1196 static void Yield();
1201 This is the entry point of the thread.
1203 This function is pure virtual and must be implemented by any derived class.
1204 The thread execution will start here.
1206 The returned value is the thread exit code which is only useful for
1207 joinable threads and is the value returned by Wait().
1208 This function is called by wxWidgets itself and should never be called
1211 virtual ExitCode
Entry() = 0;
1214 This is a protected function of the wxThread class and thus can only be called
1215 from a derived class. It also can only be called in the context of this
1216 thread, i.e. a thread can only exit from itself, not from another thread.
1218 This function will terminate the OS thread (i.e. stop the associated path of
1219 execution) and also delete the associated C++ object for detached threads.
1220 OnExit() will be called just before exiting.
1222 void Exit(ExitCode exitcode
= 0);
1226 /** See wxSemaphore. */
1229 wxSEMA_NO_ERROR
= 0,
1230 wxSEMA_INVALID
, //!< semaphore hasn't been initialized successfully
1231 wxSEMA_BUSY
, //!< returned by TryWait() if Wait() would block
1232 wxSEMA_TIMEOUT
, //!< returned by WaitTimeout()
1233 wxSEMA_OVERFLOW
, //!< Post() would increase counter past the max
1240 wxSemaphore is a counter limiting the number of threads concurrently accessing
1241 a shared resource. This counter is always between 0 and the maximum value
1242 specified during the semaphore creation. When the counter is strictly greater
1243 than 0, a call to wxSemaphore::Wait() returns immediately and decrements the
1244 counter. As soon as it reaches 0, any subsequent calls to wxSemaphore::Wait
1245 block and only return when the semaphore counter becomes strictly positive
1246 again as the result of calling wxSemaphore::Post which increments the counter.
1248 In general, semaphores are useful to restrict access to a shared resource
1249 which can only be accessed by some fixed number of clients at the same time.
1250 For example, when modeling a hotel reservation system a semaphore with the counter
1251 equal to the total number of available rooms could be created. Each time a room
1252 is reserved, the semaphore should be acquired by calling wxSemaphore::Wait
1253 and each time a room is freed it should be released by calling wxSemaphore::Post.
1256 @category{threading}
1262 Specifying a @a maxcount of 0 actually makes wxSemaphore behave as if
1263 there is no upper limit. If @a maxcount is 1, the semaphore behaves almost as a
1264 mutex (but unlike a mutex it can be released by a thread different from the one
1267 @a initialcount is the initial value of the semaphore which must be between
1268 0 and @a maxcount (if it is not set to 0).
1270 wxSemaphore(int initialcount
= 0, int maxcount
= 0);
1273 Destructor is not virtual, don't use this class polymorphically.
1278 Increments the semaphore count and signals one of the waiting
1279 threads in an atomic way. Returns @e wxSEMA_OVERFLOW if the count
1280 would increase the counter past the maximum.
1283 - wxSEMA_NO_ERROR: There was no error.
1284 - wxSEMA_INVALID : Semaphore hasn't been initialized successfully.
1285 - wxSEMA_OVERFLOW: Post() would increase counter past the max.
1286 - wxSEMA_MISC_ERROR: Miscellaneous error.
1291 Same as Wait(), but returns immediately.
1294 - wxSEMA_NO_ERROR: There was no error.
1295 - wxSEMA_INVALID: Semaphore hasn't been initialized successfully.
1296 - wxSEMA_BUSY: Returned by TryWait() if Wait() would block, i.e. the count is zero.
1297 - wxSEMA_MISC_ERROR: Miscellaneous error.
1299 wxSemaError
TryWait();
1302 Wait indefinitely until the semaphore count becomes strictly positive
1303 and then decrement it and return.
1306 - wxSEMA_NO_ERROR: There was no error.
1307 - wxSEMA_INVALID: Semaphore hasn't been initialized successfully.
1308 - wxSEMA_MISC_ERROR: Miscellaneous error.
1313 Same as Wait(), but with a timeout limit.
1316 - wxSEMA_NO_ERROR: There was no error.
1317 - wxSEMA_INVALID: Semaphore hasn't been initialized successfully.
1318 - wxSEMA_TIMEOUT: Timeout occurred without receiving semaphore.
1319 - wxSEMA_MISC_ERROR: Miscellaneous error.
1321 wxSemaError
WaitTimeout(unsigned long timeout_millis
);
1327 @class wxMutexLocker
1329 This is a small helper class to be used with wxMutex objects.
1331 A wxMutexLocker acquires a mutex lock in the constructor and releases
1332 (or unlocks) the mutex in the destructor making it much more difficult to
1333 forget to release a mutex (which, in general, will promptly lead to serious
1334 problems). See wxMutex for an example of wxMutexLocker usage.
1337 @category{threading}
1339 @see wxMutex, wxCriticalSectionLocker
1345 Constructs a wxMutexLocker object associated with mutex and locks it.
1346 Call IsOk() to check if the mutex was successfully locked.
1348 wxMutexLocker(wxMutex
& mutex
);
1351 Destructor releases the mutex if it was successfully acquired in the ctor.
1356 Returns @true if mutex was acquired in the constructor, @false otherwise.
1363 The possible wxMutex kinds.
1367 /** Normal non-recursive mutex: try to always use this one. */
1370 /** Recursive mutex: don't use these ones with wxCondition. */
1376 The possible wxMutex errors.
1380 /** The operation completed successfully. */
1381 wxMUTEX_NO_ERROR
= 0,
1383 /** The mutex hasn't been initialized. */
1386 /** The mutex is already locked by the calling thread. */
1389 /** The mutex is already locked by another thread. */
1392 /** An attempt to unlock a mutex which is not locked. */
1395 /** wxMutex::LockTimeout() has timed out. */
1398 /** Any other error */
1406 A mutex object is a synchronization object whose state is set to signaled when
1407 it is not owned by any thread, and nonsignaled when it is owned. Its name comes
1408 from its usefulness in coordinating mutually-exclusive access to a shared
1409 resource as only one thread at a time can own a mutex object.
1411 Mutexes may be recursive in the sense that a thread can lock a mutex which it
1412 had already locked before (instead of dead locking the entire process in this
1413 situation by starting to wait on a mutex which will never be released while the
1414 thread is waiting) but using them is not recommended under Unix and they are
1415 @b not recursive by default. The reason for this is that recursive
1416 mutexes are not supported by all Unix flavours and, worse, they cannot be used
1419 For example, when several threads use the data stored in the linked list,
1420 modifications to the list should only be allowed to one thread at a time
1421 because during a new node addition the list integrity is temporarily broken
1422 (this is also called @e program @e invariant).
1425 // this variable has an "s_" prefix because it is static: seeing an "s_" in
1426 // a multithreaded program is in general a good sign that you should use a
1427 // mutex (or a critical section)
1428 static wxMutex *s_mutexProtectingTheGlobalData;
1430 // we store some numbers in this global array which is presumably used by
1431 // several threads simultaneously
1434 void MyThread::AddNewNode(int num)
1436 // ensure that no other thread accesses the list
1437 s_mutexProtectingTheGlobalList->Lock();
1441 s_mutexProtectingTheGlobalList->Unlock();
1444 // return true if the given number is greater than all array elements
1445 bool MyThread::IsGreater(int num)
1447 // before using the list we must acquire the mutex
1448 wxMutexLocker lock(s_mutexProtectingTheGlobalData);
1450 size_t count = s_data.Count();
1451 for ( size_t n = 0; n < count; n++ )
1453 if ( s_data[n] > num )
1461 Notice how wxMutexLocker was used in the second function to ensure that the
1462 mutex is unlocked in any case: whether the function returns true or false
1463 (because the destructor of the local object @e lock is always called).
1464 Using this class instead of directly using wxMutex is, in general, safer
1465 and is even more so if your program uses C++ exceptions.
1468 @category{threading}
1470 @see wxThread, wxCondition, wxMutexLocker, wxCriticalSection
1476 Default constructor.
1478 wxMutex(wxMutexType type
= wxMUTEX_DEFAULT
);
1481 Destroys the wxMutex object.
1486 Locks the mutex object.
1487 This is equivalent to LockTimeout() with infinite timeout.
1489 @return One of: @c wxMUTEX_NO_ERROR, @c wxMUTEX_DEAD_LOCK.
1491 wxMutexError
Lock();
1494 Try to lock the mutex object during the specified time interval.
1496 @return One of: @c wxMUTEX_NO_ERROR, @c wxMUTEX_DEAD_LOCK, @c wxMUTEX_TIMEOUT.
1498 wxMutexError
LockTimeout(unsigned long msec
);
1501 Tries to lock the mutex object. If it can't, returns immediately with an error.
1503 @return One of: @c wxMUTEX_NO_ERROR, @c wxMUTEX_BUSY.
1505 wxMutexError
TryLock();
1508 Unlocks the mutex object.
1510 @return One of: @c wxMUTEX_NO_ERROR, @c wxMUTEX_UNLOCKED.
1512 wxMutexError
Unlock();
1517 // ============================================================================
1518 // Global functions/macros
1519 // ============================================================================
1521 /** @ingroup group_funcmacro_thread */
1525 This macro declares a (static) critical section object named @a cs if
1526 @c wxUSE_THREADS is 1 and does nothing if it is 0.
1528 @header{wx/thread.h}
1530 #define wxCRIT_SECT_DECLARE(cs)
1533 This macro declares a critical section object named @a cs if
1534 @c wxUSE_THREADS is 1 and does nothing if it is 0. As it doesn't include
1535 the @c static keyword (unlike wxCRIT_SECT_DECLARE()), it can be used to
1536 declare a class or struct member which explains its name.
1538 @header{wx/thread.h}
1540 #define wxCRIT_SECT_DECLARE_MEMBER(cs)
1543 This macro creates a wxCriticalSectionLocker named @a name and associated
1544 with the critical section @a cs if @c wxUSE_THREADS is 1 and does nothing
1547 @header{wx/thread.h}
1549 #define wxCRIT_SECT_LOCKER(name, cs)
1552 This macro combines wxCRIT_SECT_DECLARE() and wxCRIT_SECT_LOCKER(): it
1553 creates a static critical section object and also the lock object
1554 associated with it. Because of this, it can be only used inside a function,
1555 not at global scope. For example:
1560 static int s_counter = 0;
1562 wxCRITICAL_SECTION(counter);
1568 Note that this example assumes that the function is called the first time
1569 from the main thread so that the critical section object is initialized
1570 correctly by the time other threads start calling it, if this is not the
1571 case this approach can @b not be used and the critical section must be made
1574 @header{wx/thread.h}
1576 #define wxCRITICAL_SECTION(name)
1579 This macro is equivalent to
1580 @ref wxCriticalSection::Leave "critical_section.Leave()" if
1581 @c wxUSE_THREADS is 1 and does nothing if it is 0.
1583 @header{wx/thread.h}
1585 #define wxLEAVE_CRIT_SECT(critical_section)
1588 This macro is equivalent to
1589 @ref wxCriticalSection::Enter "critical_section.Enter()" if
1590 @c wxUSE_THREADS is 1 and does nothing if it is 0.
1592 @header{wx/thread.h}
1594 #define wxENTER_CRIT_SECT(critical_section)
1597 Returns @true if this thread is the main one. Always returns @true if
1598 @c wxUSE_THREADS is 0.
1600 @header{wx/thread.h}
1602 bool wxIsMainThread();
1605 This function must be called when any thread other than the main GUI thread
1606 wants to get access to the GUI library. This function will block the
1607 execution of the calling thread until the main thread (or any other thread
1608 holding the main GUI lock) leaves the GUI library and no other thread will
1609 enter the GUI library until the calling thread calls wxMutexGuiLeave().
1611 Typically, these functions are used like this:
1614 void MyThread::Foo(void)
1616 // before doing any GUI calls we must ensure that
1617 // this thread is the only one doing it!
1622 my_window-DrawSomething();
1628 This function is only defined on platforms which support preemptive
1631 @note Under GTK, no creation of top-level windows is allowed in any thread
1634 @header{wx/thread.h}
1636 void wxMutexGuiEnter();
1639 This function is only defined on platforms which support preemptive
1642 @see wxMutexGuiEnter()
1644 @header{wx/thread.h}
1646 void wxMutexGuiLeave();