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Date: Mon, 11 Oct 2004 15:17:27 +0300 (EEST) From: Hannu Savolainen Subject: Re: SDL uses obsolete OSS features I did some work on getting OSS to work better with SDL. There have been some problems with select which should be fixed now. I'm having some problems in understanding what is the purpose of the DSP_WaitAudio() routine. I added a return to the very beginning of this routine and commendted out the define for USE_BLOCKING_WRITES. At least lbreakout2 seems to work as well as earlier. The latencies are the same. An ordinary blocking write does exactly the same thing than DSP_WaitAudio does. So I would recommend using the USE_BLOCKING_WRITES approach and removing everything from the DSP_WaitAudio routine. Also enabling USE_BLOCKING_WRITES makes it possible to simplify DSP_PlayAudio() because you don't need to handle the partial writes (the do-while loop). Attached is a patch against SDL-1.2.7. After these changes SDL will use OSS as it's designed to be used (make it as simple as possible). This code should work with all OSS implementations because it uses only the very fundamental features that have been there since the jurassic times.
author Sam Lantinga <slouken@libsdl.org>
date Fri, 12 Nov 2004 21:39:04 +0000
parents 355632dca928
children
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<HTML
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><TITLE
>SDL_SemTryWait</TITLE
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><H1
><A
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></A
>SDL_SemTryWait</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8069"
></A
><H2
>Name</H2
>SDL_SemTryWait&nbsp;--&nbsp;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
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