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, 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 i
  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 a
  31 very poor choice (example: launching a separate thread when doing a long
  32 computation to show a progress dialog). Other implementation choices are
  33 available: for the progress dialog example it is far better to do the
  34 calculations in the idle handler (see wxIdleEvent) or even simply do everything
  35 at once but call wxWindow::Update() periodically to update the screen.
  36
  37 If you do decide to use threads in your application, it is strongly recommended
  38 that no more than one thread calls GUI functions. The thread sample shows that
  39 it @e is possible for many different threads to call GUI functions at once (all
  40 the threads created in the sample access GUI), but it is a very poor design
  41 choice for anything except an example. The design which uses one GUI thread and
  42 several worker threads which communicate with the main one using events is much
  43 more robust and will undoubtedly save you countless problems (example: under
  44 Win32 a thread can only access GDI objects such as pens, brushes, c created by
  45 itself and not by the other threads).
  46
  47 For communication between secondary threads and the main thread, you may use
  48 wxEvtHandler::QueueEvent or its short version ::wxQueueEvent. These functions
  49 have a thread-safe implementation so that they can be used as they are for
  50 sending events from one thread to another. However there is no built in method
  51 to send messages to the worker threads and you will need to use the available
  52 synchronization classes to implement the solution which suits your needs
  53 yourself. In particular, please note that it is not enough to derive
  54 your class from wxThread and wxEvtHandler to send messages to it: in fact, this
  55 does not work at all.
  56
  57 */
  58