20e85460c4
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@1837 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
44 lines
2.5 KiB
TeX
44 lines
2.5 KiB
TeX
\section{Multithreading overview}\label{wxthreadoverview}
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Classes: \helpref{wxThread}{wxthread}, \helpref{wxMutex}{wxmutex},
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\helpref{wxCriticalSection}{wxcriticalsection},
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\helpref{wxCondition}{wxcondition}
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wxWindows provides a complete set of classes encapsulating objects necessary in
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multithreaded (MT) programs: the \helpref{thread}{wxthread} class itself and different
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synchronization objects: \helpref{mutexes}{wxmutex} and
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\helpref{critical sections}{wxcriticalsection} with
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\helpref{conditions}{wxcondition}.
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These classes will hopefully make writing MT programs easier and they also
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provide some extra error checking (compared to the native (be it Win32 or Posix)
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thread API), however it is still an untrivial undertaking especially for large
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projects. Before starting an MT application (or starting to add MT features to
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an existing one) it is worth asking oneself if there is no easier and safer way
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to implement the same functionality. Of course, in some situations threads
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really make sense (classical example is a server application which launches a
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new thread for each new client), but in others it might be a very poor choice
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(example: launching a separate thread when doing a long computation to show a
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progress dialog). Other implementation choices are available: for the progress
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dialog example it is far better to do the calculations in the
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\helpref{idle handler}{wxidleevent} or call \helpref{wxYield()}{wxyield}
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periodically to update the screen.
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If you do decide to use threads in your application, it is strongly recommended
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that no more than one thread calls GUI functions. The thread sample shows that
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it {\it is} possible for many different threads to call GUI functions at once
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(all the threads created in the sample access GUI), but it is a very poor design
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choice for anything except an example. The design which uses one GUI thread and
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several worker threads which communicate with the main one using events is much
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more robust and will undoubtedly save you countless problems (example: under
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Win32 a thread can only access GDI objects such as pens, brushes, \&c created by
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itself and not by the other threads).
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Final note: in the current release of wxWindows, there are no specific
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facilities for communicating between the threads. However, the usual
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\helpref{ProcessEvent()}{wxevthandlerprocessevent} function may be used for
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thread communication too - but you should provide your own synchronisation
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mechanism if you use it (e.g. just use a critical section before sending a
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message) because there is no built-in synchronisation.
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