c6427d4da4
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57448 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
64 lines
3.4 KiB
C
64 lines
3.4 KiB
C
/////////////////////////////////////////////////////////////////////////////
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// Name: thread.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_thread Multithreading
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Classes: wxThread, wxThreadHelper, wxMutex, wxCriticalSection, wxCondition, wxSemaphore
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wxWidgets provides a complete set of classes encapsulating objects necessary in
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multithreaded (MT) programs: the wxThread class itself and different
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synchronization objects: mutexes (see wxMutex) and critical sections (see
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wxCriticalSection) with conditions (see wxCondition). The thread API in
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wxWidgets resembles to POSIX1.c threads API (a.k.a. pthreads), although several
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functions have different names and some features inspired by Win32 thread API
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are there as well.
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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
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Posix) thread API), however it is still a non-trivial undertaking especially
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for large projects. Before starting an MT application (or starting to add MT
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features to an existing one) it is worth asking oneself if there is no easier
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and safer way to implement the same functionality. Of course, in some
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situations threads really make sense (classical example is a server application
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which launches a new thread for each new client), but in others it might be an
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overkill. On the other hand, the recent evolution of the computer hardware shows
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an important trend towards multi-core systems, which are better exploited using
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multiple threads (e.g. you may want to split a long task among as many threads
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as many CPU (cores) the system reports; see wxThread::GetCPUCount).
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To implement non-blocking operations without using multiple threads you have
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two other possible implementation choices:
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- using wxIdleEvent (e.g. to perform a long calculation while updating a progress dialog)
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- simply do everything at once but call wxWindow::Update() periodically to update the screen.
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Even if there are the ::wxMutexGuiEnter and ::wxMutexGuiLeave functions which allows
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to use GUI functions from multiple threads, if you do decide to use threads in your
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application, it is strongly recommended that <b>no more than one calls GUI functions</b>.
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The design which uses one GUI thread and several worker threads which communicate
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with the main one using @b events is much more robust and will undoubtedly save you
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countless problems (example: under Win32 a thread can only access GDI objects such
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as pens, brushes, c created by itself and not by the other threads).
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For communication between secondary threads and the main thread, you may use
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wxEvtHandler::QueueEvent or its short version ::wxQueueEvent. These functions
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have a thread-safe implementation so that they can be used as they are for
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sending events from one thread to another. However there is no built in method
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to send messages to the worker threads and you will need to use the available
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synchronization classes to implement the solution which suits your needs
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yourself. In particular, please note that it is not enough to derive
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your class from wxThread and wxEvtHandler to send messages to it: in fact, this
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does not work at all.
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See also the @sample{thread} for a sample showing some simple interactions
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between the main and secondary threads.
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*/
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