docs/doxygen/overviews/thread.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        thread.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_thread Multithreading
  12
  13 Classes: wxThread, wxThreadHelper, wxMutex, wxCriticalSection, wxCondition, wxSemaphore
  14
  15 wxWidgets provides a complete set of classes encapsulating objects necessary in
  16 multithreaded (MT) programs: the wxThread class itself and different
  17 synchronization objects: mutexes (see wxMutex) and critical sections (see
  18 wxCriticalSection)  with conditions (see wxCondition). The thread API in
  19 wxWidgets resembles to POSIX1.c threads API (a.k.a. pthreads), although several
  20 functions have different names and some features inspired by Win32 thread API
  21 are there as well.
  22
  23 These classes will hopefully make writing MT programs easier and they also
  24 provide some extra error checking (compared to the native (be it Win32 or
  25 Posix) thread API), however it is still a non-trivial undertaking especially
  26 for large projects. Before starting an MT application (or starting to add MT
  27 features to an existing one) it is worth asking oneself if there is no easier
  28 and safer way to implement the same functionality. Of course, in some
  29 situations threads really make sense (classical example is a server application
  30 which launches a new thread for each new client), but in others it might be an
  31 overkill. On the other hand, the recent evolution of the computer hardware shows
  32 an important trend towards multi-core systems, which are better exploited using
  33 multiple threads (e.g. you may want to split a long task among as many threads
  34 as many CPU (cores) the system reports; see wxThread::GetCPUCount).
  35
  36 To implement non-blocking operations without using multiple threads you have
  37 two other possible implementation choices:
  38 - using wxIdleEvent (e.g. to perform a long calculation while updating a progress dialog)
  39 - simply do everything at once but call wxWindow::Update() periodically to update the screen.
  40
  41 Even if there are the ::wxMutexGuiEnter and ::wxMutexGuiLeave functions which allows
  42 to use GUI functions from multiple threads, if you do decide to use threads in your
  43 application, it is strongly recommended that <b>no more than one calls GUI functions</b>.
  44 The design which uses one GUI thread and several worker threads which communicate
  45 with the main one using @b events is much more robust and will undoubtedly save you
  46 countless problems (example: under Win32 a thread can only access GDI objects such
  47 as pens, brushes, c created by itself and not by the other threads).
  48
  49 For communication between secondary threads and the main thread, you may use
  50 wxEvtHandler::QueueEvent or its short version ::wxQueueEvent. These functions
  51 have a thread-safe implementation so that they can be used as they are for
  52 sending events from one thread to another. However there is no built in method
  53 to send messages to the worker threads and you will need to use the available
  54 synchronization classes to implement the solution which suits your needs
  55 yourself. In particular, please note that it is not enough to derive
  56 your class from wxThread and wxEvtHandler to send messages to it: in fact, this
  57 does not work at all.
  58
  59 See also the @sample{thread} for a sample showing some simple interactions
  60 between the main and secondary threads.
  61
  62 */
  63