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	1	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
	2	%% Name: semaphore.tex
	3	%% Purpose: wxSemaphore documentation
	4	%% Author: Vadim Zeitlin
	5	%% Modified by:
	6	%% Created: 02.04.02
	7	%% RCS-ID: $Id$
	8	%% Copyright: (c) 2002 Vadim Zeitlin
	9	%% License: wxWindows license
	10	%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
	11
	12	\section{\class{wxSemaphore}}\label{wxsemaphore}
	13
	14	wxSemaphore is a counter limiting the number of threads concurrently accessing
	15	a shared resource. This counter is always between $0$ and the maximum value
	16	specified during the semaphore creation. When the counter is strictly greater
	17	than $0$, a call to \helpref{Wait}{wxsemaphorewait} returns immediately and
	18	decrements the counter. As soon as it reaches $0$, any subsequent calls to
	19	\helpref{Wait}{wxsemaphorewait} block and only return when the semaphore
	20	counter becomes strictly positive again as the result of calling
	21	\helpref{Post}{wxsemaphorepost} which increments the counter.
	22
	23	In general, semaphores are useful to restrict access to a shared resource
	24	which can only be accessed by some fixed number of clients at the same time. For
	25	example, when modeling a hotel reservation system a semaphore with the counter
	26	equal to the total number of available rooms could be created. Each time a room
	27	is reserved, the semaphore should be acquired by calling
	28	\helpref{Wait}{wxsemaphorewait} and each time a room is freed it should be
	29	released by calling \helpref{Post}{wxsemaphorepost}.
	30
	31	\wxheading{Derived from}
	32
	33	No base class
	34
	35	\wxheading{Include files}
	36
	37	<wx/thread.h>
	38
	39	\wxheading{Library}
	40
	41	\helpref{wxBase}{librarieslist}
	42
	43	\latexignore{\rtfignore{\wxheading{Members}}}
	44
	45	\membersection{wxSemaphore::wxSemaphore}\label{wxsemaphorewxsemaphore}
	46
	47	\func{}{wxSemaphore}{\param{int }{initialcount = 0}, \param{int }{maxcount = 0}}
	48
	49	Specifying a {\it maxcount} of $0$ actually makes wxSemaphore behave as if
	50	there is no upper limit. If maxcount is $1$, the semaphore behaves exactly as a
	51	mutex.
	52
	53	{\it initialcount} is the initial value of the semaphore which must be between
	54	$0$ and {\it maxcount} (if it is not set to $0$).
	55
	56	\membersection{wxSemaphore::\destruct{wxSemaphore}}\label{wxsemaphoredtor}
	57
	58	\func{}{\destruct{wxSemaphore}}{\void}
	59
	60	Destructor is not virtual, don't use this class polymorphically.
	61
	62	\membersection{wxSemaphore::Post}\label{wxsemaphorepost}
	63
	64	\func{wxSemaError }{Post}{\void}
	65
	66	Increments the semaphore count and signals one of the waiting
	67	threads in an atomic way. Returns wxSEMA\_OVERFLOW if the count
	68	would increase the counter past the maximum.
	69
	70	\wxheading{Return value}
	71
	72	One of:
	73
	74	\twocolwidtha{7cm}
	75	\begin{twocollist}\itemsep=0pt
	76	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	77	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	78	\twocolitem{{\bf wxSEMA\_OVERFLOW}}{Post() would increase counter past the max.}
	79	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	80	\end{twocollist}
	81
	82
	83	\membersection{wxSemaphore::TryWait}\label{wxsemaphoretrywait}
	84
	85	\func{wxSemaError }{TryWait}{\void}
	86
	87	Same as \helpref{Wait()}{wxsemaphorewait}, but returns immediately.
	88
	89	\wxheading{Return value}
	90
	91	One of:
	92
	93	\twocolwidtha{7cm}
	94	\begin{twocollist}\itemsep=0pt
	95	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	96	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	97	\twocolitem{{\bf wxSEMA\_BUSY}}{Returned by TryWait() if Wait() would block, i.e. the count is zero.}
	98	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	99	\end{twocollist}
	100
	101
	102	\membersection{wxSemaphore::Wait}\label{wxsemaphorewait}
	103
	104	\func{wxSemaError }{Wait}{\void}
	105
	106	Wait indefinitely until the semaphore count becomes strictly positive
	107	and then decrement it and return.
	108
	109	\wxheading{Return value}
	110
	111	One of:
	112
	113	\twocolwidtha{7cm}
	114	\begin{twocollist}\itemsep=0pt
	115	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	116	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	117	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	118	\end{twocollist}
	119
	120	\membersection{wxSemaphore::WaitTimeout}\label{wxsemaphorewaittimeout}
	121
	122	\func{wxSemaError }{WaitTimeout}{\param{unsigned
	123	long}{timeout\_millis}}
	124
	125	Same as \helpref{Wait()}{wxsemaphorewait}, but with a timeout
	126	limit.
	127
	128	\wxheading{Return value}
	129
	130	One of:
	131
	132	\twocolwidtha{7cm}
	133	\begin{twocollist}\itemsep=0pt
	134	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	135	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	136	\twocolitem{{\bf wxSEMA\_TIMEOUT}}{Timeout occurred without receiving semaphore.}
	137	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	138	\end{twocollist}