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<HTML
><HEAD
><TITLE
>SDL_SemTryWait</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
"><LINK
REL="HOME"
TITLE="SDL Library Documentation"
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>SDL Library Documentation</TH
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><HR
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><H1
><A
NAME="SDLSEMTRYWAIT"
></A
>SDL_SemTryWait</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8069"
></A
><H2
>Name</H2
>SDL_SemTryWait -- Attempt to lock a semaphore but don't suspend the thread.</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN8072"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN8073"
></A
><P
></P
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include "SDL.h"
#include "SDL_thread.h"</PRE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int <B
CLASS="FSFUNC"
>SDL_SemTryWait</B
></CODE
>(SDL_sem *sem);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8079"
></A
><H2
>Description</H2
><P
><TT
CLASS="FUNCTION"
>SDL_SemTryWait</TT
> is a non-blocking varient of
<A
HREF="sdlsemwait.html"
><TT
CLASS="FUNCTION"
>SDL_SemWait</TT
></A
>. If the value of the semaphore
pointed to by <TT
CLASS="PARAMETER"
><I
>sem</I
></TT
> is positive it will atomically
decrement the semaphore value and return 0, otherwise it will return
<SPAN
CLASS="RETURNVALUE"
>SDL_MUTEX_TIMEDOUT</SPAN
> instead of suspending the thread.</P
><P
>After <TT
CLASS="FUNCTION"
>SDL_SemTryWait</TT
> is successful, the semaphore
can be released and its count atomically incremented by a successful call to
<A
HREF="sdlsempost.html"
>SDL_SemPost</A
>.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8090"
></A
><H2
>Return Value</H2
><P
>Returns <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> if the semaphore was successfully locked or
either <SPAN
CLASS="RETURNVALUE"
>SDL_MUTEX_TIMEDOUT</SPAN
> or <SPAN
CLASS="RETURNVALUE"
>-1</SPAN
>
if the thread would have suspended or there was an error, respectivly.</P
><P
>If the semaphore was not successfully locked, the semaphore will be unchanged.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8097"
></A
><H2
>Examples</H2
><P
><PRE
CLASS="PROGRAMLISTING"
>res = SDL_SemTryWait(my_sem);
if (res == SDL_MUTEX_TIMEDOUT) {
return TRY_AGAIN;
}
if (res == -1) {
return WAIT_ERROR;
}
...
SDL_SemPost(my_sem);</PRE
></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN8101"
></A
><H2
>See Also</H2
><P
><A
HREF="sdlcreatesemaphore.html"
><TT
CLASS="FUNCTION"
>SDL_CreateSemaphore</TT
></A
>,
<A
HREF="sdldestroysemaphore.html"
><TT
CLASS="FUNCTION"
>SDL_DestroySemaphore</TT
></A
>,
<A
HREF="sdlsemwait.html"
><TT
CLASS="FUNCTION"
>SDL_SemWait</TT
></A
>,
<A
HREF="sdlsemwaittimeout.html"
><TT
CLASS="FUNCTION"
>SDL_SemWaitTimeout</TT
></A
>,
<A
HREF="sdlsempost.html"
><TT
CLASS="FUNCTION"
>SDL_SemPost</TT
></A
>,
<A
HREF="sdlsemvalue.html"
><TT
CLASS="FUNCTION"
>SDL_SemValue</TT
></A
></P
></DIV
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