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     NOTE: we explicitely don't name wxMutexGUIEnter() and wxMutexGUILeave()
  11           as they're not safe. See also ticket #10366.
  12 */
  13
  14 /**
  15
  16 @page overview_thread Multithreading
  17
  18 Classes: wxThread, wxThreadHelper, wxMutex, wxCriticalSection, wxCondition, wxSemaphore
  19
  20 wxWidgets provides a complete set of classes encapsulating objects necessary in
  21 multithreaded (MT) programs: the wxThread class itself and different
  22 synchronization objects: mutexes (see wxMutex) and critical sections (see
  23 wxCriticalSection)  with conditions (see wxCondition). The thread API in
  24 wxWidgets resembles to POSIX1.c threads API (a.k.a. pthreads), although several
  25 functions have different names and some features inspired by Win32 thread API
  26 are there as well.
  27
  28 These classes hopefully make writing MT programs easier and they also
  29 provide some extra error checking (compared to the native - be it Win32 or
  30 Posix - thread API), however it is still a non-trivial undertaking especially
  31 for large projects.
  32 Before starting an MT application (or starting to add MT
  33 features to an existing one) it is worth asking oneself if there is no easier
  34 and safer way to implement the same functionality.
  35 Of course, in some situations threads really make sense (classical example is a
  36 server application which launches a new thread for each new client), but in others
  37 it might be an overkill.
  38 On the other hand, the recent evolution of the computer hardware shows
  39 an important trend towards multi-core systems, which are better exploited using
  40 multiple threads (e.g. you may want to split a long task among as many threads
  41 as many CPU (cores) the system reports; see wxThread::GetCPUCount).
  42
  43 To implement non-blocking operations @e without using multiple threads you have
  44 two possible implementation choices:
  45 - use wxIdleEvent (e.g. to perform a long calculation while updating a progress dialog)
  46 - do everything at once but call wxWindow::Update() or wxApp::YieldFor(wxEVT_CATEGORY_UI)
  47   periodically to update the screen.
  48
  49 If instead you choose to use threads in your application, it is strongly recommended
  50 that <b>no secondary threads call GUI functions</b>.
  51 The design which uses one GUI thread and several worker threads which communicate
  52 with the main one using @b events is much more robust and will undoubtedly save you
  53 countless problems (example: under Win32 a thread can only access GDI objects such
  54 as pens, brushes, c created by itself and not by the other threads).
  55
  56 For communication between secondary threads and the main thread, you may use
  57 wxEvtHandler::QueueEvent or its short version ::wxQueueEvent. These functions
  58 have a thread-safe implementation so that they can be used as they are for
  59 sending events from one thread to another. However there is no built in method
  60 to send messages to the worker threads and you will need to use the available
  61 synchronization classes to implement the solution which suits your needs
  62 yourself. In particular, please note that it is not enough to derive
  63 your class from wxThread and wxEvtHandler to send messages to it: in fact, this
  64 does not work at all.
  65
  66 See also the @sample{thread} for a sample showing some simple interactions
  67 between the main and secondary threads.
  68
  69 */
  70