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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, the semaphores are useful to restrict access to a shared resource
	24	which can only be accessed by some fixed number of clients at once. 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	\latexignore{\rtfignore{\wxheading{Members}}}
	40
	41	\membersection{wxSemaphore::wxSemaphore}\label{wxsemaphorewxsemaphore}
	42
	43	\func{}{wxSemaphore}{\param{int }{initialcount = 0}, \param{int }{maxcount = 0}}
	44
	45	Specifying a {\it maxcount} of $0$ actually makes wxSemaphore behave as if
	46	there is no upper limit. If maxcount is $1$ the semaphore behaves exactly as a
	47	mutex.
	48
	49	{\it initialcount} is the initial value of the semaphore which must be between
	50	$0$ and {\it maxcount} (if it is not set to $0$).
	51
	52	\membersection{wxSemaphore::\destruct{wxSemaphore}}\label{wxsemaphoredtor}
	53
	54	\func{}{\destruct{wxSemaphore}}{\void}
	55
	56	Destructor is not virtual, don't use this class polymorphically.
	57
	58	\membersection{wxSemaphore::Post}\label{wxsemaphorepost}
	59
	60	\func{wxSemaError }{Post}{\void}
	61
	62	Increments the semaphore count and signals one of the waiting
	63	threads in an atomic way. Returns wxSEMA\_OVERFLOW if the count
	64	would increase the counter past the maximum.
	65
	66	\wxheading{Return value}
	67
	68	One of:
	69
	70	\twocolwidtha{7cm}
	71	\begin{twocollist}\itemsep=0pt
	72	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	73	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	74	\twocolitem{{\bf wxSEMA\_OVERFLOW}}{Post() would increase counter past the max.}
	75	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	76	\end{twocollist}
	77
	78
	79	\membersection{wxSemaphore::TryWait}\label{wxsemaphoretrywait}
	80
	81	\func{wxSemaError }{TryWait}{\void}
	82
	83	Same as \helpref{Wait()}{wxsemaphorewait}, but returns immediately.
	84
	85	\wxheading{Return value}
	86
	87	One of:
	88
	89	\twocolwidtha{7cm}
	90	\begin{twocollist}\itemsep=0pt
	91	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	92	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	93	\twocolitem{{\bf wxSEMA\_BUSY}}{Returned by TryWait() if Wait() would block, i.e. the count is zero.}
	94	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	95	\end{twocollist}
	96
	97
	98	\membersection{wxSemaphore::Wait}\label{wxsemaphorewait}
	99
	100	\func{wxSemaError }{Wait}{\void}
	101
	102	Wait indefinitely until the semaphore count becomes strictly positive
	103	and then decrement it and return.
	104
	105	\wxheading{Return value}
	106
	107	One of:
	108
	109	\twocolwidtha{7cm}
	110	\begin{twocollist}\itemsep=0pt
	111	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	112	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	113	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	114	\end{twocollist}
	115
	116	\membersection{wxSemaphore::WaitTimeout}\label{wxsemaphorewaittimeout}
	117
	118	\func{wxSemaError }{WaitTimeout}{\param{unsigned
	119	long}{timeout\_millis}}
	120
	121	Same as \helpref{Wait()}{wxsemaphorewait}, but with a timeout
	122	limit.
	123
	124	\wxheading{Return value}
	125
	126	One of:
	127
	128	\twocolwidtha{7cm}
	129	\begin{twocollist}\itemsep=0pt
	130	\twocolitem{{\bf wxSEMA\_NO\_ERROR}}{There was no error.}
	131	\twocolitem{{\bf wxSEMA\_INVALID}}{Semaphore hasn't been initialized successfully.}
	132	\twocolitem{{\bf wxSEMA\_TIMEOUT}}{Timeout occurred without receiving semaphore.}
	133	\twocolitem{{\bf wxSEMA\_MISC\_ERROR}}{Miscellaneous error.}
	134	\end{twocollist}