X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/be8098689121d2352751c51005c133797d77ecea..65baafba0e8cd74f2264b7e2f7625ff5bea84864:/docs/latex/wx/conditn.tex diff --git a/docs/latex/wx/conditn.tex b/docs/latex/wx/conditn.tex index bb71a7e7d7..c39e2c1689 100644 --- a/docs/latex/wx/conditn.tex +++ b/docs/latex/wx/conditn.tex @@ -13,8 +13,12 @@ worker threads it already makes much more sense). Note that a call to \helpref{Signal()}{wxconditionsignal} may happen before the other thread calls \helpref{Wait()}{wxconditionwait} and, just as with the -pthread conditions, the signal is then lost and so if you want to be sure to -get it you must use a mutex together with the condition variable. +pthread conditions, the signal is then lost and so if you want to be sure that +you don't miss it you must keep the mutex associated with the condition +initially locked and lock it again before calling +\helpref{Signal()}{wxconditionsignal}. Of course, this means that this call is +going to block until \helpref{Wait()}{wxconditionwait} is called by another +thread. \wxheading{Example} @@ -22,10 +26,10 @@ This example shows how a main thread may launch a worker thread which starts running and then waits until the main thread signals it to continue: \begin{verbatim} -class MyWaitingThread : public wxThread +class MySignallingThread : public wxThread { public: - MyWaitingThread(wxMutex *mutex, wxCondition *condition) + MySignallingThread(wxMutex *mutex, wxCondition *condition) { m_mutex = mutex; m_condition = condition; @@ -35,45 +39,64 @@ public: virtual ExitCode Entry() { - // wait for the signal from the main thread: it is absolutely necessary - // to look the mutex before doing it! - m_mutex->Lock(); - m_condition->Signal(); - m_mutex->Unlock(); - ... do our job ... + // tell the other(s) thread(s) that we're about to terminate: we must + // lock the mutex first or we might signal the condition before the + // waiting threads start waiting on it! + wxMutexLocker lock(m_mutex); + m_condition.Broadcast(); // same as Signal() here -- one waiter only + return 0; } private: wxCondition *m_condition; + wxMutex *m_mutex; }; int main() { wxMutex mutex; - wxCondition condition(&mutex); - - for ( int i = 0; i < 10; i++ ) - { - MyWaitingThread *thread = new MyWaitingThread(&mutex, &condition); + wxCondition condition(mutex); - thread->Run(); - } + // the mutex should be initially locked + mutex.Lock(); - // wake up one of the threads - condition.Signal(); + // create and run the thread but notice that it won't be able to + // exit (and signal its exit) before we unlock the mutex below + MySignallingThread *thread = new MySignallingThread(&mutex, &condition); - // wake up all the other ones - condition.Broadcast(); + thread->Run(); - ... wait until they terminate or do something else ... + // wait for the thread termination: Wait() atomically unlocks the mutex + // which allows the thread to continue and starts waiting + condition.Wait(); + // now we can exit return 0; } \end{verbatim} +Of course, here it would be much better to simply use a joinable thread and +call \helpref{wxThread::Wait}{wxthreadwait} on it, but this example does +illustrate the importance of properly locking the mutex when using +wxCondition. + +\wxheading{Constants} + +The following return codes are returned by wxCondition member functions: + +\begin{verbatim} +enum wxCondError +{ + wxCOND_NO_ERROR = 0, // successful completion + wxCOND_INVALID, // object hasn't been initialized successfully + wxCOND_TIMEOUT, // WaitTimeout() has timed out + wxCOND_MISC_ERROR // some other error +}; +\end{verbatim} + \wxheading{Derived from} None. @@ -88,13 +111,17 @@ None. \latexignore{\rtfignore{\wxheading{Members}}} -\membersection{wxCondition::wxCondition}\label{wxconditionconstr} +\membersection{wxCondition::wxCondition}\label{wxconditionctor} + +\func{}{wxCondition}{\param{wxMutex\& }{mutex}} -\func{}{wxCondition}{\param{wxMutex }{*mutex}} +Default and only constructor. The {\it mutex} must be locked by the caller +before calling \helpref{Wait}{wxconditionwait} function. -Default and only constructor. The {\it mutex} must be non {\tt NULL}. +Use \helpref{IsOk}{wxconditionisok} to check if the object was successfully +initialized. -\membersection{wxCondition::\destruct{wxCondition}} +\membersection{wxCondition::\destruct{wxCondition}}\label{wxconditiondtor} \func{}{\destruct{wxCondition}}{\void} @@ -113,6 +140,13 @@ not. \helpref{wxCondition::Signal}{wxconditionsignal} +\membersection{wxCondition::IsOk}\label{wxconditionisok} + +\constfunc{bool}{IsOk}{\void} + +Returns {\tt true} if the object had been initialized successfully, {\tt false} +if an error occurred. + \membersection{wxCondition::Signal}\label{wxconditionsignal} \func{void}{Signal}{\void} @@ -131,26 +165,46 @@ condition is locked or not. \membersection{wxCondition::Wait}\label{wxconditionwait} -\func{void}{Wait}{\void} +\func{wxCondError}{Wait}{\void} Waits until the condition is signalled. -\func{bool}{Wait}{\param{unsigned long}{ sec}, \param{unsigned long}{ nsec}} +This method atomically releases the lock on the mutex associated with this +condition (this is why it must be locked prior to calling Wait) and puts the +thread to sleep until \helpref{Signal}{wxconditionsignal} or +\helpref{Broadcast}{wxconditionbroadcast} is called. + +Note that even if \helpref{Signal}{wxconditionsignal} had been called before +Wait without waking up any thread, the thread would still wait for another one +and so it is important to ensure that the condition will be signalled after +Wait or the thread may sleep forever. + +\wxheading{Return value} + +Returns {\tt wxCOND\_NO\_ERROR} on success, another value if an error occurred. + +\wxheading{See also} + +\helpref{WaitTimeout}{wxconditionwaittimeout} + + +\membersection{wxCondition::WaitTimeout}\label{wxconditionwaittimeout} + +\func{wxCondError}{WaitTimeout}{\param{unsigned long}{ milliseconds}} Waits until the condition is signalled or the timeout has elapsed. -Note that the mutex associated with this condition {\bf must} be acquired by -the thread before calling this method. +This method is identical to \helpref{Wait}{wxconditionwait} except that it +returns, with the return code of {\tt wxCOND\_TIMEOUT} as soon as the given +timeout expires. \wxheading{Parameters} -\docparam{sec}{Timeout in seconds} - -\docparam{nsec}{Timeout nanoseconds component (added to {\it sec}).} +\docparam{milliseconds}{Timeout in milliseconds} \wxheading{Return value} -The second form returns {\tt TRUE} if the condition has been signalled, or -{\tt FALSE} if it returned because the timeout has elapsed. - +Returns {\tt wxCOND\_NO\_ERROR} if the condition was signalled, +{\tt wxCOND\_TIMEOUT} if the timeout elapsed before this happened or another +error code from wxCondError enum.