docs/latex/wx/semaphor.tex

   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{void}{Post}{\void}
  61
  62 Increments the semaphore count and signals one of the waiting threads in an
  63 atomic way.
  64
  65 \membersection{wxSemaphore::TryWait}\label{wxsemaphoretrywait}
  66
  67 \func{bool}{TryWait}{\void}
  68
  69 Same as \helpref{Wait()}{wxsemaphorewait}, but does not block, returns
  70 {\tt TRUE} if the semaphore was successfully acquired and {\tt FALSE} if the
  71 count is zero and it couldn't be done.
  72
  73 \membersection{wxSemaphore::Wait}\label{wxsemaphorewait}
  74
  75 \func{void}{Wait}{\void}
  76
  77 Wait indefinitely until the semaphore count becomes strictly positive
  78 and then decrement it and return.
  79
  80 \func{bool}{Wait}{\param{unsigned long }{timeout\_millis}}
  81
  82 Same as the version above, but with a timeout limit: returns {\tt TRUE} if the
  83 semaphore was acquired and {\tt FALSE} if the timeout has elapsed
  84