fixed another return FALSE in a function returning a pointer (patch 545046)

[wxWidgets.git] / docs / latex / wx / conditn.tex

diff --git a/docs/latex/wx/conditn.tex b/docs/latex/wx/conditn.tex
index 88b04eeb289e3870c86d28d97960011e28080d2b..44ba4395096cba093bed5a68f6f8afc1a2e9d351 100644 (file)
--- a/docs/latex/wx/conditn.tex
+++ b/docs/latex/wx/conditn.tex
@@ -12,28 +12,22 @@ perfect because in this particular case it would be much better to just
 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} but, in marked contrast
-with the pthread conditions, this will still work as the missed signals are
-queued and \helpref{Wait()}{wxconditionwait} simply returns immediately if
-there are ny pending signals.
-
-However, the calls to \helpref{Broadcast()}{wxconditionbroadcast} are {\bf not} 
-queued and so it will only wake up the threads already waiting on the
-condition. Accordingly, you will probably want to use a mutex to ensure that
-the thread(s) you want to be waken up have indeed started to wait before
-calling \helpref{Broadcast()}{wxconditionbroadcast}.
+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.
 
 \wxheading{Example}
 
-This example shows how a main thread may launch a worker thread and wait until
-it starts running:
+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
 {
 public:
-    MyWaitingThread(wxCondition *condition)
+    MyWaitingThread(wxMutex *mutex, wxCondition *condition)
     {
+        m_mutex = mutex;
         m_condition = condition;
 
         Create();
@@ -41,8 +35,11 @@ public:
 
     virtual ExitCode Entry()
     {
-        // let the main thread know that we started running
+        // 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 ...
 
@@ -55,15 +52,23 @@ private:
 
 int main()
 {
-    wxCondition condition;
-    MyWaitingThread *thread - new MyWaitingThread(&condition);
+    wxMutex mutex;
+    wxCondition condition(mutex);
+
+    for ( int i = 0; i < 10; i++ )
+    {
+        MyWaitingThread *thread = new MyWaitingThread(&mutex, &condition);
 
-    thread->Run();
+        thread->Run();
+    }
 
-    // wait until the thread really starts running
-    condition.Wait();
+    // wake up one of the threads
+    condition.Signal();
 
-    ...
+    // wake up all the other ones
+    condition.Broadcast();
+
+    ... wait until they terminate or do something else ...
 
     return 0;
 }
@@ -85,37 +90,58 @@ None.
 
 \membersection{wxCondition::wxCondition}\label{wxconditionconstr}
 
-\func{}{wxCondition}{\void}
+\func{}{wxCondition}{\param{wxMutex\& }{mutex}}
 
-Default constructor.
+Default and only constructor. The {\it mutex} must be locked by the caller
+before calling \helpref{Wait}{wxconditionwait} function.
 
 \membersection{wxCondition::\destruct{wxCondition}}
 
 \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::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}{\void}
 
-Waits indefinitely.
+Waits until the condition is signalled.
 
 \func{bool}{Wait}{\param{unsigned long}{ sec}, \param{unsigned long}{ nsec}}
 
-Waits until a signal is raised or the timeout has elapsed.
+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.
 
 \wxheading{Parameters}
 
@@ -125,5 +151,7 @@ Waits until a signal is raised or the timeout has elapsed.
 
 \wxheading{Return value}
 
-The second form returns if the signal was raised, or FALSE if there was a timeout.
+The second form returns {\tt TRUE} if the condition has been signalled, or
+{\tt FALSE} if it returned because the timeout has elapsed.
+