3f66f6a5b3
This keyword is not expanded by Git which means it's not replaced with the correct revision value in the releases made using git-based scripts and it's confusing to have lines with unexpanded "$Id$" in the released files. As expanding them with Git is not that simple (it could be done with git archive and export-subst attribute) and there are not many benefits in having them in the first place, just remove all these lines. If nothing else, this will make an eventual transition to Git simpler. Closes #14487. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74602 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
90 lines
4.3 KiB
C
90 lines
4.3 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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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/*
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NOTE: we explicitly don't name wxMutexGUIEnter() and wxMutexGUILeave()
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as they're not safe. See also ticket #10366.
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*/
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/**
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@page overview_thread Multithreading Overview
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@tableofcontents
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wxWidgets provides a complete set of classes encapsulating objects necessary in
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multi-threaded (MT) applications: 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 hopefully make writing MT programs easier and they also provide
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some extra error checking (compared to the native - be it Win32 or Posix -
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thread API), however it is still a non-trivial 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 an overkill. On the
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other hand, the recent evolution of the computer hardware shows an important
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trend towards multi-core systems, which are better exploited using multiple
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threads (e.g. you may want to split a long task among as many threads as many
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CPU (cores) the system reports; see wxThread::GetCPUCount).
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To implement non-blocking operations @e without using multiple threads you have
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two possible implementation choices:
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- use wxIdleEvent (e.g. to perform a long calculation while updating a progress dialog)
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- do everything at once but call wxWindow::Update() or wxApp::YieldFor(wxEVT_CATEGORY_UI)
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periodically to update the screen.
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If instead you choose to use threads in your application, please read the
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following section of this overview.
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@see wxThread, wxThreadHelper, wxMutex, wxCriticalSection, wxCondition,
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wxSemaphore
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@section overview_thread_notes Important Notes for Multi-threaded Applications
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When writing a multi-threaded application, it is strongly recommended that
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<b>no secondary threads call GUI functions</b>. The design which uses one GUI
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thread and several worker threads which communicate with the main one using
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@b events is much more robust and will undoubtedly save you countless problems
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(example: under Win32 a thread can only access GDI objects such as pens,
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brushes, device contexts 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 your class
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from wxThread and wxEvtHandler to send messages to it: in fact, this does not
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work at all. You're instead encouraged to use wxThreadHelper as it greatly
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simplifies the communication and the sharing of resources.
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You should also look at the wxThread docs for important notes about secondary
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threads and their deletion.
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Last, remember that if wxEventLoopBase::YieldFor() is used directly or
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indirectly (e.g. through wxProgressDialog) in your code, then you may have both
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re-entrancy problems and also problems caused by the processing of events out
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of order. To resolve the last problem wxThreadEvent can be used: thanks to its
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implementation of the wxThreadEvent::GetEventCategory function wxThreadEvent
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classes in fact do not get processed by wxEventLoopBase::YieldFor() unless you
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specify the @c wxEVT_CATEGORY_THREAD flag.
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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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