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1\section{Multithreading overview}\label{wxthreadoverview}
2
3Classes: \helpref{wxThread}{wxthread}, \helpref{wxMutex}{wxmutex},
4\helpref{wxCriticalSection}{wxcriticalsection},
5\helpref{wxCondition}{wxcondition}
6
7wxWidgets provides a complete set of classes encapsulating objects necessary in
8multithreaded (MT) programs: the \helpref{thread}{wxthread} class itself and different
9synchronization objects: \helpref{mutexes}{wxmutex} and
10\helpref{critical sections}{wxcriticalsection} with
11\helpref{conditions}{wxcondition}. The thread API in wxWidgets resembles to
12POSIX1.c threads API (a.k.a. pthreads), although several functions have
13different names and some features inspired by Win32 thread API are there as
14well.
15
16These classes will hopefully make writing MT programs easier and they also
17provide some extra error checking (compared to the native (be it Win32 or Posix)
18thread API), however it is still an non-trivial undertaking especially for large
19projects. Before starting an MT application (or starting to add MT features to
20an existing one) it is worth asking oneself if there is no easier and safer way
21to implement the same functionality. Of course, in some situations threads
22really make sense (classical example is a server application which launches a
23new thread for each new client), but in others it might be a very poor choice
24(example: launching a separate thread when doing a long computation to show a
25progress dialog). Other implementation choices are available: for the progress
26dialog example it is far better to do the calculations in the
27\helpref{idle handler}{wxidleevent} or call \helpref{wxYield()}{wxyield}
28periodically to update the screen.
29
30If you do decide to use threads in your application, it is strongly recommended
31that no more than one thread calls GUI functions. The thread sample shows that
32it {\it is} possible for many different threads to call GUI functions at once
33(all the threads created in the sample access GUI), but it is a very poor design
34choice for anything except an example. The design which uses one GUI thread and
35several worker threads which communicate with the main one using events is much
36more robust and will undoubtedly save you countless problems (example: under
37Win32 a thread can only access GDI objects such as pens, brushes, \&c created by
38itself and not by the other threads).
39
40For communication between threads, use
41\helpref{wxEvtHandler::AddPendingEvent}{wxevthandleraddpendingevent}
42or its short version \helpref{wxPostEvent}{wxpostevent}. These functions
43have thread safe implementation so that they can be used as they are for
44sending event from one thread to another.
45
46