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 overview
  12
  13  Classes: #wxThread, #wxMutex, #wxCriticalSection, #wxCondition
  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 wxWidgets
  19  resembles to POSIX1.c threads API (a.k.a. pthreads), although several functions have
  20  different names and some features inspired by Win32 thread API are there as well.
  21
  22  These classes will hopefully make writing MT programs easier and they also
  23  provide some extra error checking (compared to the native (be it Win32 or Posix)
  24  thread API), however it is still a non-trivial undertaking especially for large
  25  projects. Before starting an MT application (or starting to add MT features to
  26  an existing one) it is worth asking oneself if there is no easier and safer way
  27  to implement the same functionality. Of course, in some situations threads
  28  really make sense (classical example is a server application which launches a
  29  new thread for each new client), but in others it might be a very poor choice
  30  (example: launching a separate thread when doing a long computation to show a
  31  progress dialog). Other implementation choices are available: for the progress
  32  dialog example it is far better to do the calculations in the idle handler
  33  (see @ref wxIdleEvent) or even simply do everything at once but call wxWindow::Update()
  34  periodically to update the screen.
  35
  36  If you do decide to use threads in your application, it is strongly recommended
  37  that no more than one thread calls GUI functions. The thread sample shows that
  38  it @e is possible for many different threads to call GUI functions at once
  39  (all the threads created in the sample access GUI), but it is a very poor design
  40  choice for anything except an example. The design which uses one GUI thread and
  41  several worker threads which communicate with the main one using events is much
  42  more robust and will undoubtedly save you countless problems (example: under
  43  Win32 a thread can only access GDI objects such as pens, brushes, c created by
  44  itself and not by the other threads).
  45
  46  For communication between secondary threads and the main thread, you may use
  47  wxEvtHandler::AddPendingEvent or its short version #wxPostEvent. These functions
  48  have a thread-safe implementation so that they can be used as they are for
  49  sending events from one thread to another. However there is no built in method
  50  to send messages to the worker threads and you will need to use the available
  51  synchronization classes to implement the solution which suits your needs
  52  yourself. In particular, please note that it is not enough to derive
  53  your class from #wxThread and #wxEvtHandler to send messages to it:
  54  in fact, this does not work at all.
  55
  56 */
  57