docs/latex/wx/tthreads.tex

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