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mention multi-core systems and wxThread::GetCPUCount

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git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57448 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Francesco Montorsi
2008-12-20 21:26:25 +00:00
parent 267400868a
commit c6427d4da4
2 changed files with 27 additions and 18 deletions
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39
docs/doxygen/overviews/thread.h
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@@ -10,12 +10,12 @@
@page overview_thread Multithreading
Classes: wxThread, wxMutex, wxCriticalSection, wxCondition
Classes: wxThread, wxThreadHelper, wxMutex, wxCriticalSection, wxCondition, wxSemaphore
wxWidgets provides a complete set of classes encapsulating objects necessary in
multithreaded (MT) programs: the wxThread class itself and different
synchronization objects: mutexes (see wxMutex) and critical sections (see
wxCriticalSection) with conditions (see wxCondition). The thread API i
wxCriticalSection) with conditions (see wxCondition). The thread API in
wxWidgets resembles to POSIX1.c threads API (a.k.a. pthreads), although several
functions have different names and some features inspired by Win32 thread API
are there as well.
@@ -27,22 +27,24 @@ for large projects. Before starting an MT application (or starting to add MT
features to an existing one) it is worth asking oneself if there is no easier
and safer way to implement the same functionality. Of course, in some
situations threads really make sense (classical example is a server application
which launches a new thread for each new client), but in others it might be a
very poor choice (example: launching a separate thread when doing a long
computation to show a progress dialog). Other implementation choices are
available: for the progress dialog example it is far better to do the
calculations in the idle handler (see wxIdleEvent) or even simply do everything
at once but call wxWindow::Update() periodically to update the screen.
which launches a new thread for each new client), but in others it might be an
overkill. On the other hand, the recent evolution of the computer hardware shows
an important trend towards multi-core systems, which are better exploited using
multiple threads (e.g. you may want to split a long task among as many threads
as many CPU (cores) the system reports; see wxThread::GetCPUCount).
If you do decide to use threads in your application, it is strongly recommended
that no more than one thread calls GUI functions. The thread sample shows that
it @e is possible for many different threads to call GUI functions at once (all
the threads created in the sample access GUI), but it is a very poor design
choice for anything except an example. The design which uses one GUI thread and
several worker threads which communicate with the main one using events is much
more robust and will undoubtedly save you countless problems (example: under
Win32 a thread can only access GDI objects such as pens, brushes, c created by
itself and not by the other threads).
To implement non-blocking operations without using multiple threads you have
two other possible implementation choices:
- using wxIdleEvent (e.g. to perform a long calculation while updating a progress dialog)
- simply do everything at once but call wxWindow::Update() periodically to update the screen.
Even if there are the ::wxMutexGuiEnter and ::wxMutexGuiLeave functions which allows
to use GUI functions from multiple threads, if you do decide to use threads in your
application, it is strongly recommended that <b>no more than one calls GUI functions</b>.
The design which uses one GUI thread and several worker threads which communicate
with the main one using @b events is much more robust and will undoubtedly save you
countless problems (example: under Win32 a thread can only access GDI objects such
as pens, brushes, c created by itself and not by the other threads).
For communication between secondary threads and the main thread, you may use
wxEvtHandler::QueueEvent or its short version ::wxQueueEvent. These functions
@@ -54,5 +56,8 @@ yourself. In particular, please note that it is not enough to derive
your class from wxThread and wxEvtHandler to send messages to it: in fact, this
does not work at all.
See also the @sample{thread} for a sample showing some simple interactions
between the main and secondary threads.
*/