interface/thread.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        thread.h
   3 // Purpose:     interface of wxCondition
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10     @class wxCondition
  11     @wxheader{thread.h}
  12
  13     wxCondition variables correspond to pthread conditions or to Win32 event
  14     objects. They may be used in a multithreaded application to wait until the
  15     given condition becomes @true which happens when the condition becomes signaled.
  16
  17     For example, if a worker thread is doing some long task and another thread has
  18     to wait until it is finished, the latter thread will wait on the condition
  19     object and the worker thread will signal it on exit (this example is not
  20     perfect because in this particular case it would be much better to just
  21     wxThread::Wait for the worker thread, but if there are several
  22     worker threads it already makes much more sense).
  23
  24     Note that a call to wxCondition::Signal may happen before the
  25     other thread calls wxCondition::Wait and, just as with the
  26     pthread conditions, the signal is then lost and so if you want to be sure that
  27     you don't miss it you must keep the mutex associated with the condition
  28     initially locked and lock it again before calling
  29     wxCondition::Signal. Of course, this means that this call is
  30     going to block until wxCondition::Wait is called by another
  31     thread.
  32
  33     @library{wxbase}
  34     @category{thread}
  35
  36     @see wxThread, wxMutex
  37 */
  38 class wxCondition
  39 {
  40 public:
  41     /**
  42         Default and only constructor. The @a mutex must be locked by the caller
  43         before calling Wait() function.
  44         Use IsOk() to check if the object was successfully
  45         initialized.
  46     */
  47     wxCondition(wxMutex& mutex);
  48
  49     /**
  50         Destroys the wxCondition object. The destructor is not virtual so this class
  51         should not be used polymorphically.
  52     */
  53     ~wxCondition();
  54
  55     /**
  56         Broadcasts to all waiting threads, waking all of them up. Note that this method
  57         may be called whether the mutex associated with this condition is locked or
  58         not.
  59
  60         @see Signal()
  61     */
  62     void Broadcast();
  63
  64     /**
  65         Returns @true if the object had been initialized successfully, @false
  66         if an error occurred.
  67     */
  68     bool IsOk() const;
  69
  70     /**
  71         Signals the object waking up at most one thread. If several threads are waiting
  72         on the same condition, the exact thread which is woken up is undefined. If no
  73         threads are waiting, the signal is lost and the condition would have to be
  74         signalled again to wake up any thread which may start waiting on it later.
  75         Note that this method may be called whether the mutex associated with this
  76         condition is locked or not.
  77
  78         @see Broadcast()
  79     */
  80     void Signal();
  81
  82     /**
  83         Waits until the condition is signalled.
  84         This method atomically releases the lock on the mutex associated with this
  85         condition (this is why it must be locked prior to calling Wait) and puts the
  86         thread to sleep until Signal() or
  87         Broadcast() is called. It then locks the mutex
  88         again and returns.
  89         Note that even if Signal() had been called before
  90         Wait without waking up any thread, the thread would still wait for another one
  91         and so it is important to ensure that the condition will be signalled after
  92         Wait or the thread may sleep forever.
  93
  94         @return Returns wxCOND_NO_ERROR on success, another value if an error
  95                  occurred.
  96
  97         @see WaitTimeout()
  98     */
  99     wxCondError Wait();
 100
 101     /**
 102         Waits until the condition is signalled or the timeout has elapsed.
 103         This method is identical to Wait() except that it
 104         returns, with the return code of @c wxCOND_TIMEOUT as soon as the given
 105         timeout expires.
 106
 107         @param milliseconds
 108             Timeout in milliseconds
 109     */
 110     wxCondError WaitTimeout(unsigned long milliseconds);
 111 };
 112
 113
 114
 115 /**
 116     @class wxCriticalSectionLocker
 117     @wxheader{thread.h}
 118
 119     This is a small helper class to be used with wxCriticalSection
 120     objects. A wxCriticalSectionLocker enters the critical section in the
 121     constructor and leaves it in the destructor making it much more difficult to
 122     forget to leave a critical section (which, in general, will lead to serious
 123     and difficult to debug problems).
 124
 125     Example of using it:
 126
 127     @code
 128     void Set Foo()
 129     {
 130         // gs_critSect is some (global) critical section guarding access to the
 131         // object "foo"
 132         wxCriticalSectionLocker locker(gs_critSect);
 133
 134         if ( ... )
 135         {
 136             // do something
 137             ...
 138
 139             return;
 140         }
 141
 142         // do something else
 143         ...
 144
 145         return;
 146     }
 147     @endcode
 148
 149     Without wxCriticalSectionLocker, you would need to remember to manually leave
 150     the critical section before each @c return.
 151
 152     @library{wxbase}
 153     @category{thread}
 154
 155     @see wxCriticalSection, wxMutexLocker
 156 */
 157 class wxCriticalSectionLocker
 158 {
 159 public:
 160     /**
 161         Constructs a wxCriticalSectionLocker object associated with given
 162         @a criticalsection and enters it.
 163     */
 164     wxCriticalSectionLocker(wxCriticalSection& criticalsection);
 165
 166     /**
 167         Destructor leaves the critical section.
 168     */
 169     ~wxCriticalSectionLocker();
 170 };
 171
 172
 173
 174 /**
 175     @class wxThreadHelper
 176     @wxheader{thread.h}
 177
 178     The wxThreadHelper class is a mix-in class that manages a single background
 179     thread.  By deriving from wxThreadHelper, a class can implement the thread
 180     code in its own wxThreadHelper::Entry method
 181     and easily share data and synchronization objects between the main thread
 182     and the worker thread.  Doing this prevents the awkward passing of pointers
 183     that is needed when the original object in the main thread needs to
 184     synchronize with its worker thread in its own wxThread derived object.
 185
 186     For example, wxFrame may need to make some calculations
 187     in a background thread and then display the results of those calculations in
 188     the main window.
 189
 190     Ordinarily, a wxThread derived object would be created
 191     with the calculation code implemented in
 192     wxThread::Entry.  To access the inputs to the
 193     calculation, the frame object would often to pass a pointer to itself to the
 194     thread object.  Similarly, the frame object would hold a pointer to the
 195     thread object.  Shared data and synchronization objects could be stored in
 196     either object though the object without the data would have to access the
 197     data through a pointer.
 198
 199     However, with wxThreadHelper, the frame object and the thread object are
 200     treated as the same object.  Shared data and synchronization variables are
 201     stored in the single object, eliminating a layer of indirection and the
 202     associated pointers.
 203
 204     @library{wxbase}
 205     @category{thread}
 206
 207     @see wxThread
 208 */
 209 class wxThreadHelper
 210 {
 211 public:
 212     /**
 213         This constructor simply initializes a member variable.
 214     */
 215     wxThreadHelper();
 216
 217     /**
 218         The destructor frees the resources associated with the thread.
 219     */
 220     ~wxThreadHelper();
 221
 222     /**
 223         Creates a new thread. The thread object is created in the suspended state, and
 224         you
 225         should call @ref wxThread::run GetThread()-Run to start running
 226         it.  You may optionally specify the stack size to be allocated to it (Ignored on
 227         platforms that don't support setting it explicitly, eg. Unix).
 228
 229         @return One of:
 230     */
 231     wxThreadError Create(unsigned int stackSize = 0);
 232
 233     /**
 234         This is the entry point of the thread. This function is pure virtual and must
 235         be implemented by any derived class. The thread execution will start here.
 236         The returned value is the thread exit code which is only useful for
 237         joinable threads and is the value returned by
 238         @ref wxThread::wait GetThread()-Wait.
 239         This function is called by wxWidgets itself and should never be called
 240         directly.
 241     */
 242     virtual ExitCode Entry();
 243
 244     /**
 245         This is a public function that returns the wxThread object
 246         associated with the thread.
 247     */
 248     wxThread* GetThread();
 249
 250     /**
 251         wxThread * m_thread
 252         the actual wxThread object.
 253     */
 254 };
 255
 256
 257
 258 /**
 259     @class wxCriticalSection
 260     @wxheader{thread.h}
 261
 262     A critical section object is used for exactly the same purpose as
 263     mutexes(). The only difference is that under Windows platform
 264     critical sections are only visible inside one process, while mutexes may be
 265     shared between processes, so using critical sections is slightly more
 266     efficient. The terminology is also slightly different: mutex may be locked (or
 267     acquired) and unlocked (or released) while critical section is entered and left
 268     by the program.
 269
 270     Finally, you should try to use
 271     wxCriticalSectionLocker class whenever
 272     possible instead of directly using wxCriticalSection for the same reasons
 273     wxMutexLocker is preferrable to
 274     wxMutex - please see wxMutex for an example.
 275
 276     @library{wxbase}
 277     @category{thread}
 278
 279     @see wxThread, wxCondition, wxCriticalSectionLocker
 280 */
 281 class wxCriticalSection
 282 {
 283 public:
 284     /**
 285         Default constructor initializes critical section object.
 286     */
 287     wxCriticalSection();
 288
 289     /**
 290         Destructor frees the resources.
 291     */
 292     ~wxCriticalSection();
 293
 294     /**
 295         Enter the critical section (same as locking a mutex). There is no error return
 296         for this function. After entering the critical section protecting some global
 297         data the thread running in critical section may safely use/modify it.
 298     */
 299     void Enter();
 300
 301     /**
 302         Leave the critical section allowing other threads use the global data protected
 303         by it. There is no error return for this function.
 304     */
 305     void Leave();
 306 };
 307
 308
 309
 310 /**
 311     @class wxThread
 312     @wxheader{thread.h}
 313
 314     A thread is basically a path of execution through a program. Threads are
 315     sometimes called @e light-weight processes, but the fundamental difference
 316     between threads and processes is that memory spaces of different processes are
 317     separated while all threads share the same address space.
 318
 319     While it makes it much easier to share common data between several threads, it
 320     also
 321     makes it much easier to shoot oneself in the foot, so careful use of
 322     synchronization
 323     objects such as mutexes() or @ref overview_wxcriticalsection "critical
 324     sections" is recommended. In addition, don't create global thread
 325     objects because they allocate memory in their constructor, which will cause
 326     problems for the memory checking system.
 327
 328     @library{wxbase}
 329     @category{thread}
 330
 331     @see wxMutex, wxCondition, wxCriticalSection
 332 */
 333 class wxThread
 334 {
 335 public:
 336     /**
 337         This constructor creates a new detached (default) or joinable C++ thread
 338         object. It
 339         does not create or start execution of the real thread -- for this you should
 340         use the Create() and Run() methods.
 341         The possible values for @a kind parameters are:
 342
 343         @b wxTHREAD_DETACHED
 344
 345         Creates a detached thread.
 346
 347         @b wxTHREAD_JOINABLE
 348
 349         Creates a joinable thread.
 350     */
 351     wxThread(wxThreadKind kind = wxTHREAD_DETACHED);
 352
 353     /**
 354         The destructor frees the resources associated with the thread. Notice that you
 355         should never delete a detached thread -- you may only call
 356         Delete() on it or wait until it terminates (and auto
 357         destructs) itself. Because the detached threads delete themselves, they can
 358         only be allocated on the heap.
 359         Joinable threads should be deleted explicitly. The Delete() and Kill() functions
 360         will not delete the C++ thread object. It is also safe to allocate them on
 361         stack.
 362     */
 363     ~wxThread();
 364
 365     /**
 366         Creates a new thread. The thread object is created in the suspended state, and
 367         you
 368         should call Run() to start running it.  You may optionally
 369         specify the stack size to be allocated to it (Ignored on platforms that don't
 370         support setting it explicitly, eg. Unix system without
 371         @c pthread_attr_setstacksize). If you do not specify the stack size,
 372         the system's default value is used.
 373         @b Warning: It is a good idea to explicitly specify a value as systems'
 374         default values vary from just a couple of KB on some systems (BSD and
 375         OS/2 systems) to one or several MB (Windows, Solaris, Linux). So, if you
 376         have a thread that requires more than just a few KB of memory, you will
 377         have mysterious problems on some platforms but not on the common ones. On the
 378         other hand, just indicating a large stack size by default will give you
 379         performance issues on those systems with small default stack since those
 380         typically use fully committed memory for the stack. On the contrary, if
 381         use a lot of threads (say several hundred), virtual adress space can get tight
 382         unless you explicitly specify a smaller amount of thread stack space for each
 383         thread.
 384
 385         @return One of:
 386     */
 387     wxThreadError Create(unsigned int stackSize = 0);
 388
 389     /**
 390         Calling Delete() gracefully terminates a
 391         detached thread, either when the thread calls TestDestroy() or finished
 392         processing.
 393         (Note that while this could work on a joinable thread you simply should not
 394         call this routine on one as afterwards you may not be able to call
 395         Wait() to free the memory of that thread).
 396         See @ref overview_deletionwxthread "wxThread deletion" for a broader
 397         explanation of this routine.
 398     */
 399     wxThreadError Delete();
 400
 401     /**
 402         A common problem users experience with wxThread is that in their main thread
 403         they will check the thread every now and then to see if it has ended through
 404         IsRunning(), only to find that their
 405         application has run into problems because the thread is using the default
 406         behavior and has already deleted itself. Naturally, they instead attempt to
 407         use joinable threads in place of the previous behavior.
 408         However, polling a wxThread for when it has ended is in general a bad idea -
 409         in fact calling a routine on any running wxThread should be avoided if
 410         possible. Instead, find a way to notify yourself when the thread has ended.
 411         Usually you only need to notify the main thread, in which case you can post
 412         an event to it via wxPostEvent() or
 413         wxEvtHandler::AddPendingEvent. In
 414         the case of secondary threads you can call a routine of another class
 415         when the thread is about to complete processing and/or set the value
 416         of a variable, possibly using mutexes() and/or other
 417         synchronization means if necessary.
 418     */
 419
 420
 421     /**
 422         This is the entry point of the thread. This function is pure virtual and must
 423         be implemented by any derived class. The thread execution will start here.
 424         The returned value is the thread exit code which is only useful for
 425         joinable threads and is the value returned by Wait().
 426         This function is called by wxWidgets itself and should never be called
 427         directly.
 428     */
 429     virtual ExitCode Entry();
 430
 431     /**
 432         This is a protected function of the wxThread class and thus can only be called
 433         from a derived class. It also can only be called in the context of this
 434         thread, i.e. a thread can only exit from itself, not from another thread.
 435         This function will terminate the OS thread (i.e. stop the associated path of
 436         execution) and also delete the associated C++ object for detached threads.
 437         OnExit() will be called just before exiting.
 438     */
 439     void Exit(ExitCode exitcode = 0);
 440
 441     /**
 442         Returns the number of system CPUs or -1 if the value is unknown.
 443
 444         @see SetConcurrency()
 445     */
 446     static int GetCPUCount();
 447
 448     /**
 449         Returns the platform specific thread ID of the current thread as a
 450         long.  This can be used to uniquely identify threads, even if they are
 451         not wxThreads.
 452     */
 453     static unsigned long GetCurrentId();
 454
 455     /**
 456         Gets the thread identifier: this is a platform dependent number that uniquely
 457         identifies the
 458         thread throughout the system during its existence (i.e. the thread identifiers
 459         may be reused).
 460     */
 461     unsigned long GetId() const;
 462
 463     /**
 464         Gets the priority of the thread, between zero and 100.
 465         The following priorities are defined:
 466
 467         @b WXTHREAD_MIN_PRIORITY
 468
 469         0
 470
 471         @b WXTHREAD_DEFAULT_PRIORITY
 472
 473         50
 474
 475         @b WXTHREAD_MAX_PRIORITY
 476
 477         100
 478     */
 479     int GetPriority() const;
 480
 481     /**
 482         Returns @true if the thread is alive (i.e. started and not terminating).
 483         Note that this function can only safely be used with joinable threads, not
 484         detached ones as the latter delete themselves and so when the real thread is
 485         no longer alive, it is not possible to call this function because
 486         the wxThread object no longer exists.
 487     */
 488     bool IsAlive() const;
 489
 490     /**
 491         Returns @true if the thread is of the detached kind, @false if it is a
 492         joinable
 493         one.
 494     */
 495     bool IsDetached() const;
 496
 497     /**
 498         Returns @true if the calling thread is the main application thread.
 499     */
 500     static bool IsMain();
 501
 502     /**
 503         Returns @true if the thread is paused.
 504     */
 505     bool IsPaused() const;
 506
 507     /**
 508         Returns @true if the thread is running.
 509         This method may only be safely used for joinable threads, see the remark in
 510         IsAlive().
 511     */
 512     bool IsRunning() const;
 513
 514     /**
 515         Immediately terminates the target thread. @b This function is dangerous and
 516         should
 517         be used with extreme care (and not used at all whenever possible)! The resources
 518         allocated to the thread will not be freed and the state of the C runtime library
 519         may become inconsistent. Use Delete() for detached
 520         threads or Wait() for joinable threads instead.
 521         For detached threads Kill() will also delete the associated C++ object.
 522         However this will not happen for joinable threads and this means that you will
 523         still have to delete the wxThread object yourself to avoid memory leaks.
 524         In neither case OnExit() of the dying thread will be
 525         called, so no thread-specific cleanup will be performed.
 526         This function can only be called from another thread context, i.e. a thread
 527         cannot kill itself.
 528         It is also an error to call this function for a thread which is not running or
 529         paused (in the latter case, the thread will be resumed first) -- if you do it,
 530         a @c wxTHREAD_NOT_RUNNING error will be returned.
 531     */
 532     wxThreadError Kill();
 533
 534     /**
 535         Called when the thread exits. This function is called in the context of the
 536         thread associated with the wxThread object, not in the context of the main
 537         thread. This function will not be called if the thread was
 538         @ref kill() killed.
 539         This function should never be called directly.
 540     */
 541     void OnExit();
 542
 543     /**
 544         Suspends the thread. Under some implementations (Win32), the thread is
 545         suspended immediately, under others it will only be suspended when it calls
 546         TestDestroy() for the next time (hence, if the
 547         thread doesn't call it at all, it won't be suspended).
 548         This function can only be called from another thread context.
 549     */
 550     wxThreadError Pause();
 551
 552     /**
 553         Resumes a thread suspended by the call to Pause().
 554         This function can only be called from another thread context.
 555     */
 556     wxThreadError Resume();
 557
 558     /**
 559         Starts the thread execution. Should be called after
 560         Create().
 561         This function can only be called from another thread context.
 562     */
 563     wxThreadError Run();
 564
 565     /**
 566         Sets the thread concurrency level for this process. This is, roughly, the
 567         number of threads that the system tries to schedule to run in parallel.
 568         The value of 0 for @a level may be used to set the default one.
 569         Returns @true on success or @false otherwise (for example, if this function is
 570         not implemented for this platform -- currently everything except Solaris).
 571     */
 572     static bool SetConcurrency(size_t level);
 573
 574     /**
 575         Sets the priority of the thread, between 0 and 100. It can only be set
 576         after calling Create() but before calling
 577         Run().
 578         The following priorities are already defined:
 579
 580         @b WXTHREAD_MIN_PRIORITY
 581
 582         0
 583
 584         @b WXTHREAD_DEFAULT_PRIORITY
 585
 586         50
 587
 588         @b WXTHREAD_MAX_PRIORITY
 589
 590         100
 591     */
 592     void SetPriority(int priority);
 593
 594     /**
 595         Pauses the thread execution for the given amount of time.
 596
 597         This is the same as wxMilliSleep().
 598     */
 599     static void Sleep(unsigned long milliseconds);
 600
 601     /**
 602         This function should be called periodically by the thread to ensure that calls
 603         to Pause() and Delete() will
 604         work. If it returns @true, the thread should exit as soon as possible.
 605         Notice that under some platforms (POSIX), implementation of
 606         Pause() also relies on this function being called, so
 607         not calling it would prevent both stopping and suspending thread from working.
 608     */
 609     virtual bool TestDestroy();
 610
 611     /**
 612         Return the thread object for the calling thread. @NULL is returned if the
 613         calling thread
 614         is the main (GUI) thread, but IsMain() should be used to test
 615         whether the thread is really the main one because @NULL may also be returned for
 616         the thread
 617         not created with wxThread class. Generally speaking, the return value for such
 618         a thread
 619         is undefined.
 620     */
 621     static wxThread* This();
 622
 623     /**
 624         There are two types of threads in wxWidgets: @e detached and @e joinable,
 625         modeled after the the POSIX thread API. This is different from the Win32 API
 626         where all threads are joinable.
 627         By default wxThreads in wxWidgets use the detached behavior. Detached threads
 628         delete themselves once they have completed, either by themselves when they
 629         complete
 630         processing or through a call to Delete(), and thus
 631         must be created on the heap (through the new operator, for example).
 632         Conversely,
 633         joinable threads do not delete themselves when they are done processing and as
 634         such
 635         are safe to create on the stack. Joinable threads also provide the ability
 636         for one to get value it returned from Entry()
 637         through Wait().
 638         You shouldn't hurry to create all the threads joinable, however, because this
 639         has a disadvantage as well: you @b must Wait() for a joinable thread or the
 640         system resources used by it will never be freed, and you also must delete the
 641         corresponding wxThread object yourself if you did not create it on the stack.
 642         In
 643         contrast, detached threads are of the "fire-and-forget" kind: you only have to
 644         start
 645         a detached thread and it will terminate and destroy itself.
 646     */
 647
 648
 649     /**
 650         Waits for a joinable thread to terminate and returns the value the thread
 651         returned from Entry() or @c (ExitCode)-1 on
 652         error. Notice that, unlike Delete() doesn't cancel the
 653         thread in any way so the caller waits for as long as it takes to the thread to
 654         exit.
 655         You can only Wait() for joinable (not detached) threads.
 656         This function can only be called from another thread context.
 657         See @ref overview_deletionwxthread "wxThread deletion" for a broader
 658         explanation of this routine.
 659     */
 660     ExitCode Wait() const;
 661
 662     /**
 663         Give the rest of the thread time slice to the system allowing the other threads
 664         to run.
 665         Note that using this function is @b strongly discouraged, since in
 666         many cases it indicates a design weakness of your threading model (as
 667         does using Sleep functions).
 668         Threads should use the CPU in an efficient manner, i.e. they should
 669         do their current work efficiently, then as soon as the work is done block
 670         on a wakeup event (wxCondition, wxMutex, select(), poll(), ...)
 671         which will get signalled e.g. by other threads or a user device once further
 672         thread work is available. Using Yield or Sleep
 673         indicates polling-type behaviour, since we're fuzzily giving up our timeslice
 674         and wait until sometime later we'll get reactivated, at which time we
 675         realize that there isn't really much to do and Yield again...
 676         The most critical characteristic of Yield is that it's operating system
 677         specific: there may be scheduler changes which cause your thread to not
 678         wake up relatively soon again, but instead many seconds later,
 679         causing huge performance issues for your application. @b with a
 680         well-behaving, CPU-efficient thread the operating system is likely to properly
 681         care for its reactivation the moment it needs it, whereas with
 682         non-deterministic, Yield-using threads all bets are off and the system
 683         scheduler is free to penalize drastically, and this effect gets worse
 684         with increasing system load due to less free CPU resources available.
 685         You may refer to various Linux kernel sched_yield discussions for more
 686         information.
 687         See also Sleep().
 688     */
 689     void Yield();
 690
 691     /**
 692         Regardless of whether it has terminated or not, you should call
 693         Wait() on a joinable thread to release its
 694         memory, as outlined in @ref overview_typeswxthread "Types of wxThreads". If you
 695         created
 696         a joinable thread on the heap, remember to delete it manually with the delete
 697         operator or similar means as only detached threads handle this type of memory
 698         management.
 699         Since detached threads delete themselves when they are finished processing,
 700         you should take care when calling a routine on one. If you are certain the
 701         thread is still running and would like to end it, you may call
 702         Delete() to gracefully end it (which implies
 703         that the thread will be deleted after that call to Delete()). It should be
 704         implied that you should never attempt to delete a detached thread with the
 705         delete operator or similar means.
 706         As mentioned, Wait() or
 707         Delete() attempts to gracefully terminate
 708         a joinable and detached thread, respectively. It does this by waiting until
 709         the thread in question calls TestDestroy()
 710         or ends processing (returns from wxThread::Entry).
 711         Obviously, if the thread does call TestDestroy() and does not end the calling
 712         thread will come to halt. This is why it is important to call TestDestroy() in
 713         the Entry() routine of your threads as often as possible.
 714         As a last resort you can end the thread immediately through
 715         Kill(). It is strongly recommended that you
 716         do not do this, however, as it does not free the resources associated with
 717         the object (although the wxThread object of detached threads will still be
 718         deleted) and could leave the C runtime library in an undefined state.
 719     */
 720
 721
 722     /**
 723         All threads other then the "main application thread" (the one
 724         wxApp::OnInit or your main function runs in, for
 725         example) are considered "secondary threads". These include all threads created
 726         by Create() or the corresponding constructors.
 727         GUI calls, such as those to a wxWindow or
 728         wxBitmap are explicitly not safe at all in secondary threads
 729         and could end your application prematurely. This is due to several reasons,
 730         including the underlying native API and the fact that wxThread does not run a
 731         GUI event loop similar to other APIs as MFC.
 732         A workaround that works on some wxWidgets ports is calling wxMutexGUIEnter()
 733         before any GUI calls and then calling wxMutexGUILeave() afterwords. However,
 734         the recommended way is to simply process the GUI calls in the main thread
 735         through an event that is posted by either wxPostEvent() or
 736         wxEvtHandler::AddPendingEvent. This does
 737         not imply that calls to these classes are thread-safe, however, as most
 738         wxWidgets classes are not thread-safe, including wxString.
 739     */
 740 };
 741
 742
 743
 744 /**
 745     @class wxSemaphore
 746     @wxheader{thread.h}
 747
 748     wxSemaphore is a counter limiting the number of threads concurrently accessing
 749     a shared resource. This counter is always between 0 and the maximum value
 750     specified during the semaphore creation. When the counter is strictly greater
 751     than 0, a call to wxSemaphore::Wait returns immediately and
 752     decrements the counter. As soon as it reaches 0, any subsequent calls to
 753     wxSemaphore::Wait block and only return when the semaphore
 754     counter becomes strictly positive again as the result of calling
 755     wxSemaphore::Post which increments the counter.
 756
 757     In general, semaphores are useful to restrict access to a shared resource
 758     which can only be accessed by some fixed number of clients at the same time. For
 759     example, when modeling a hotel reservation system a semaphore with the counter
 760     equal to the total number of available rooms could be created. Each time a room
 761     is reserved, the semaphore should be acquired by calling
 762     wxSemaphore::Wait and each time a room is freed it should be
 763     released by calling wxSemaphore::Post.
 764
 765     @library{wxbase}
 766     @category{thread}
 767 */
 768 class wxSemaphore
 769 {
 770 public:
 771     /**
 772         Specifying a @a maxcount of 0 actually makes wxSemaphore behave as if
 773         there is no upper limit. If maxcount is 1, the semaphore behaves almost as a
 774         mutex (but unlike a mutex it can be released by a thread different from the one
 775         which acquired it).
 776         @a initialcount is the initial value of the semaphore which must be between
 777         0 and @a maxcount (if it is not set to 0).
 778     */
 779     wxSemaphore(int initialcount = 0, int maxcount = 0);
 780
 781     /**
 782         Destructor is not virtual, don't use this class polymorphically.
 783     */
 784     ~wxSemaphore();
 785
 786     /**
 787         Increments the semaphore count and signals one of the waiting
 788         threads in an atomic way. Returns wxSEMA_OVERFLOW if the count
 789         would increase the counter past the maximum.
 790
 791         @return One of:
 792     */
 793     wxSemaError Post();
 794
 795     /**
 796         Same as Wait(), but returns immediately.
 797
 798         @return One of:
 799     */
 800     wxSemaError TryWait();
 801
 802     /**
 803         Wait indefinitely until the semaphore count becomes strictly positive
 804         and then decrement it and return.
 805
 806         @return One of:
 807     */
 808     wxSemaError Wait();
 809 };
 810
 811
 812
 813 /**
 814     @class wxMutexLocker
 815     @wxheader{thread.h}
 816
 817     This is a small helper class to be used with wxMutex
 818     objects. A wxMutexLocker acquires a mutex lock in the constructor and releases
 819     (or unlocks) the mutex in the destructor making it much more difficult to
 820     forget to release a mutex (which, in general, will promptly lead to serious
 821     problems). See wxMutex for an example of wxMutexLocker
 822     usage.
 823
 824     @library{wxbase}
 825     @category{thread}
 826
 827     @see wxMutex, wxCriticalSectionLocker
 828 */
 829 class wxMutexLocker
 830 {
 831 public:
 832     /**
 833         Constructs a wxMutexLocker object associated with mutex and locks it.
 834         Call @ref isok() IsLocked to check if the mutex was
 835         successfully locked.
 836     */
 837     wxMutexLocker(wxMutex& mutex);
 838
 839     /**
 840         Destructor releases the mutex if it was successfully acquired in the ctor.
 841     */
 842     ~wxMutexLocker();
 843
 844     /**
 845         Returns @true if mutex was acquired in the constructor, @false otherwise.
 846     */
 847     bool IsOk() const;
 848 };
 849
 850
 851
 852 /**
 853     @class wxMutex
 854     @wxheader{thread.h}
 855
 856     A mutex object is a synchronization object whose state is set to signaled when
 857     it is not owned by any thread, and nonsignaled when it is owned. Its name comes
 858     from its usefulness in coordinating mutually-exclusive access to a shared
 859     resource as only one thread at a time can own a mutex object.
 860
 861     Mutexes may be recursive in the sense that a thread can lock a mutex which it
 862     had already locked before (instead of dead locking the entire process in this
 863     situation by starting to wait on a mutex which will never be released while the
 864     thread is waiting) but using them is not recommended under Unix and they are
 865     @b not recursive there by default. The reason for this is that recursive
 866     mutexes are not supported by all Unix flavours and, worse, they cannot be used
 867     with wxCondition. On the other hand, Win32 mutexes are
 868     always recursive.
 869
 870     For example, when several threads use the data stored in the linked list,
 871     modifications to the list should only be allowed to one thread at a time
 872     because during a new node addition the list integrity is temporarily broken
 873     (this is also called @e program invariant).
 874
 875     @library{wxbase}
 876     @category{thread}
 877
 878     @see wxThread, wxCondition, wxMutexLocker, wxCriticalSection
 879 */
 880 class wxMutex
 881 {
 882 public:
 883     /**
 884         Default constructor.
 885     */
 886     wxMutex(wxMutexType type = wxMUTEX_DEFAULT);
 887
 888     /**
 889         Destroys the wxMutex object.
 890     */
 891     ~wxMutex();
 892
 893     /**
 894         Locks the mutex object. This is equivalent to
 895         LockTimeout() with infinite timeout.
 896
 897         @return One of:
 898     */
 899     wxMutexError Lock();
 900
 901     /**
 902         Try to lock the mutex object during the specified time interval.
 903
 904         @return One of:
 905     */
 906     wxMutexError LockTimeout(unsigned long msec);
 907
 908     /**
 909         Tries to lock the mutex object. If it can't, returns immediately with an error.
 910
 911         @return One of:
 912     */
 913     wxMutexError TryLock();
 914
 915     /**
 916         Unlocks the mutex object.
 917
 918         @return One of:
 919     */
 920     wxMutexError Unlock();
 921 };
 922
 923
 924
 925 // ============================================================================
 926 // Global functions/macros
 927 // ============================================================================
 928
 929 /** @ingroup group_funcmacro_thread */
 930 //@{
 931
 932 /**
 933     This macro declares a (static) critical section object named @a cs if
 934     @c wxUSE_THREADS is 1 and does nothing if it is 0.
 935
 936     @header{wx/thread.h}
 937 */
 938 #define wxCRIT_SECT_DECLARE(cs)
 939
 940 /**
 941     This macro declares a critical section object named @a cs if
 942     @c wxUSE_THREADS is 1 and does nothing if it is 0. As it doesn't include
 943     the @c static keyword (unlike wxCRIT_SECT_DECLARE()), it can be used to
 944     declare a class or struct member which explains its name.
 945
 946     @header{wx/thread.h}
 947 */
 948 #define wxCRIT_SECT_DECLARE_MEMBER(cs)
 949
 950 /**
 951     This macro creates a wxCriticalSectionLocker named @a name and associated
 952     with the critical section @a cs if @c wxUSE_THREADS is 1 and does nothing
 953     if it is 0.
 954
 955     @header{wx/thread.h}
 956 */
 957 #define wxCRIT_SECT_LOCKER(name, cs)
 958
 959 /**
 960     This macro combines wxCRIT_SECT_DECLARE() and wxCRIT_SECT_LOCKER(): it
 961     creates a static critical section object and also the lock object
 962     associated with it. Because of this, it can be only used inside a function,
 963     not at global scope. For example:
 964
 965     @code
 966     int IncCount()
 967     {
 968         static int s_counter = 0;
 969
 970         wxCRITICAL_SECTION(counter);
 971
 972         return ++s_counter;
 973     }
 974     @endcode
 975
 976     Note that this example assumes that the function is called the first time
 977     from the main thread so that the critical section object is initialized
 978     correctly by the time other threads start calling it, if this is not the
 979     case this approach can @b not be used and the critical section must be made
 980     a global instead.
 981
 982     @header{wx/thread.h}
 983 */
 984 #define wxCRITICAL_SECTION(name)
 985
 986 /**
 987     This macro is equivalent to
 988     @ref wxCriticalSection::Leave "critical_section.Leave()" if
 989     @c wxUSE_THREADS is 1 and does nothing if it is 0.
 990
 991     @header{wx/thread.h}
 992 */
 993 #define wxLEAVE_CRIT_SECT(critical_section)
 994
 995 /**
 996     This macro is equivalent to
 997     @ref wxCriticalSection::Enter "critical_section.Enter()" if
 998     @c wxUSE_THREADS is 1 and does nothing if it is 0.
 999
1000     @header{wx/thread.h}
1001 */
1002 #define wxENTER_CRIT_SECT(critical_section)
1003
1004 /**
1005     Returns @true if this thread is the main one. Always returns @true if
1006     @c wxUSE_THREADS is 0.
1007
1008     @header{wx/thread.h}
1009 */
1010 bool wxIsMainThread();
1011
1012 /**
1013     This function must be called when any thread other than the main GUI thread
1014     wants to get access to the GUI library. This function will block the
1015     execution of the calling thread until the main thread (or any other thread
1016     holding the main GUI lock) leaves the GUI library and no other thread will
1017     enter the GUI library until the calling thread calls wxMutexGuiLeave().
1018
1019     Typically, these functions are used like this:
1020
1021     @code
1022     void MyThread::Foo(void)
1023     {
1024         // before doing any GUI calls we must ensure that
1025         // this thread is the only one doing it!
1026
1027         wxMutexGuiEnter();
1028
1029         // Call GUI here:
1030         my_window-DrawSomething();
1031
1032         wxMutexGuiLeave();
1033     }
1034     @endcode
1035
1036     This function is only defined on platforms which support preemptive
1037     threads.
1038
1039     @note Under GTK, no creation of top-level windows is allowed in any thread
1040           but the main one.
1041
1042     @header{wx/thread.h}
1043 */
1044 void wxMutexGuiEnter();
1045
1046 /**
1047     This function is only defined on platforms which support preemptive
1048     threads.
1049
1050     @see wxMutexGuiEnter()
1051
1052     @header{wx/thread.h}
1053 */
1054 void wxMutexGuiLeave();
1055
1056 //@}
1057