X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/9063ea8ee28601bfa00b6c724847ff22eced970d..a43ec16b16cf61894294f071011ec984d8a3d673:/docs/latex/wx/conditn.tex?ds=sidebyside

diff --git a/docs/latex/wx/conditn.tex b/docs/latex/wx/conditn.tex
index 777a3cd226..1c31d62d80 100644
--- a/docs/latex/wx/conditn.tex
+++ b/docs/latex/wx/conditn.tex
@@ -5,12 +5,98 @@ objects. They may be used in a multithreaded application to wait until the
 given condition becomes true which happens when the condition becomes signaled.
 
 For example, if a worker thread is doing some long task and another thread has
-to wait until it's finished, the latter thread will wait on the condition
+to wait until it is finished, the latter thread will wait on the condition
 object and the worker thread will signal it on exit (this example is not
 perfect because in this particular case it would be much better to just 
 \helpref{Wait()}{wxthreadwait} for the worker thread, but if there are several
 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 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}
+
+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 MySignallingThread : public wxThread
+{
+public:
+    MySignallingThread(wxMutex *mutex, wxCondition *condition)
+    {
+        m_mutex = mutex;
+        m_condition = condition;
+
+        Create();
+    }
+
+    virtual ExitCode Entry()
+    {
+        ... 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);
+
+    // the mutex should be initially locked
+    mutex.Lock();
+
+    // 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);
+
+    thread->Run();
+
+    // 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.
@@ -25,49 +111,101 @@ None.
 
 \latexignore{\rtfignore{\wxheading{Members}}}
 
-\membersection{wxCondition::wxCondition}\label{wxconditionconstr}
+\membersection{wxCondition::wxCondition}\label{wxconditionctor}
+
+\func{}{wxCondition}{\param{wxMutex\& }{mutex}}
 
-\func{}{wxCondition}{\void}
+Default and only constructor. The {\it mutex} must be locked by the caller
+before calling \helpref{Wait}{wxconditionwait} function.
 
-Default constructor.
+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}
 
-Destroys the wxCondition object.
+Destroys the wxCondition object. The destructor is not virtual so this class
+should not be used polymorphically.
 
 \membersection{wxCondition::Broadcast}\label{wxconditionbroadcast}
 
 \func{void}{Broadcast}{\void}
 
-Broadcasts to all waiting objects.
+Broadcasts to all waiting threads, waking all of them up. Note that this method
+may be called whether the mutex associated with this condition is locked or
+not.
+
+\wxheading{See also}
+
+\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}
 
-Signals the object.
+Signals the object waking up at most one thread. If several threads are waiting
+on the same condition, the exact thread which is woken up is undefined. If no
+threads are waiting, the signal is lost and the condition would have to be
+signalled again to wake up any thread which may start waiting on it later.
+
+Note that this method may be called whether the mutex associated with this
+condition is locked or not.
+
+\wxheading{See also}
+
+\helpref{wxCondition::Broadcast}{wxconditionbroadcast}
 
 \membersection{wxCondition::Wait}\label{wxconditionwait}
 
-\func{void}{Wait}{\param{wxMutex\&}{ mutex}}
+\func{wxCondError}{Wait}{\void}
 
-Waits indefinitely.
+Waits until the condition is signalled.
 
-\func{bool}{Wait}{\param{wxMutex\&}{ mutex}, \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. It then locks the mutex
+again and returns.
 
-Waits until a signal is raised or the timeout has elapsed.
+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{Parameters}
+\wxheading{Return value}
+
+Returns {\tt wxCOND\_NO\_ERROR} on success, another value if an error occurred.
+
+\wxheading{See also}
+
+\helpref{WaitTimeout}{wxconditionwaittimeout}
 
-\docparam{mutex}{wxMutex object.}
 
-\docparam{sec}{Timeout in seconds}
+\membersection{wxCondition::WaitTimeout}\label{wxconditionwaittimeout}
+
+\func{wxCondError}{WaitTimeout}{\param{unsigned long}{ milliseconds}}
+
+Waits until the condition is signalled or the timeout has elapsed.
+
+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{nsec}{Timeout nanoseconds component (added to {\it sec}).}
+\docparam{milliseconds}{Timeout in milliseconds}
 
 \wxheading{Return value}
 
-The second form returns if the signal was raised, or FALSE if there was a timeout.
+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.
 
