Mercurial > sdl-ios-xcode
annotate docs/html/sdlsemwait.html @ 968:4675910b0b7b
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> |
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date | Fri, 12 Nov 2004 21:39:04 +0000 |
parents | 355632dca928 |
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rev | line source |
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0 | 1 <HTML |
2 ><HEAD | |
3 ><TITLE | |
4 >SDL_SemWait</TITLE | |
5 ><META | |
6 NAME="GENERATOR" | |
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ |
0 | 8 "><LINK |
9 REL="HOME" | |
10 TITLE="SDL Library Documentation" | |
11 HREF="index.html"><LINK | |
12 REL="UP" | |
13 TITLE="Multi-threaded Programming" | |
14 HREF="thread.html"><LINK | |
15 REL="PREVIOUS" | |
16 TITLE="SDL_DestroySemaphore" | |
17 HREF="sdldestroysemaphore.html"><LINK | |
18 REL="NEXT" | |
19 TITLE="SDL_SemTryWait" | |
20 HREF="sdlsemtrywait.html"></HEAD | |
21 ><BODY | |
22 CLASS="REFENTRY" | |
23 BGCOLOR="#FFF8DC" | |
24 TEXT="#000000" | |
25 LINK="#0000ee" | |
26 VLINK="#551a8b" | |
27 ALINK="#ff0000" | |
28 ><DIV | |
29 CLASS="NAVHEADER" | |
30 ><TABLE | |
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31 SUMMARY="Header navigation table" |
0 | 32 WIDTH="100%" |
33 BORDER="0" | |
34 CELLPADDING="0" | |
35 CELLSPACING="0" | |
36 ><TR | |
37 ><TH | |
38 COLSPAN="3" | |
39 ALIGN="center" | |
40 >SDL Library Documentation</TH | |
41 ></TR | |
42 ><TR | |
43 ><TD | |
44 WIDTH="10%" | |
45 ALIGN="left" | |
46 VALIGN="bottom" | |
47 ><A | |
48 HREF="sdldestroysemaphore.html" | |
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49 ACCESSKEY="P" |
0 | 50 >Prev</A |
51 ></TD | |
52 ><TD | |
53 WIDTH="80%" | |
54 ALIGN="center" | |
55 VALIGN="bottom" | |
56 ></TD | |
57 ><TD | |
58 WIDTH="10%" | |
59 ALIGN="right" | |
60 VALIGN="bottom" | |
61 ><A | |
62 HREF="sdlsemtrywait.html" | |
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63 ACCESSKEY="N" |
0 | 64 >Next</A |
65 ></TD | |
66 ></TR | |
67 ></TABLE | |
68 ><HR | |
69 ALIGN="LEFT" | |
70 WIDTH="100%"></DIV | |
71 ><H1 | |
72 ><A | |
73 NAME="SDLSEMWAIT" | |
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74 ></A |
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75 >SDL_SemWait</H1 |
0 | 76 ><DIV |
77 CLASS="REFNAMEDIV" | |
78 ><A | |
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79 NAME="AEN8023" |
0 | 80 ></A |
81 ><H2 | |
82 >Name</H2 | |
83 >SDL_SemWait -- Lock a semaphore and suspend the thread if the semaphore value is zero.</DIV | |
84 ><DIV | |
85 CLASS="REFSYNOPSISDIV" | |
86 ><A | |
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87 NAME="AEN8026" |
0 | 88 ></A |
89 ><H2 | |
90 >Synopsis</H2 | |
91 ><DIV | |
92 CLASS="FUNCSYNOPSIS" | |
93 ><A | |
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94 NAME="AEN8027" |
0 | 95 ></A |
96 ><P | |
97 ></P | |
98 ><PRE | |
99 CLASS="FUNCSYNOPSISINFO" | |
100 >#include "SDL.h" | |
101 #include "SDL_thread.h"</PRE | |
102 ><P | |
103 ><CODE | |
104 ><CODE | |
105 CLASS="FUNCDEF" | |
106 >int <B | |
107 CLASS="FSFUNC" | |
108 >SDL_SemWait</B | |
109 ></CODE | |
110 >(SDL_sem *sem);</CODE | |
111 ></P | |
112 ><P | |
113 ></P | |
114 ></DIV | |
115 ></DIV | |
116 ><DIV | |
117 CLASS="REFSECT1" | |
118 ><A | |
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119 NAME="AEN8033" |
0 | 120 ></A |
121 ><H2 | |
122 >Description</H2 | |
123 ><P | |
124 ><TT | |
125 CLASS="FUNCTION" | |
126 >SDL_SemWait()</TT | |
127 > suspends the calling thread until either | |
128 the semaphore pointed to by <TT | |
129 CLASS="PARAMETER" | |
130 ><I | |
131 >sem</I | |
132 ></TT | |
133 > has a positive value, | |
134 the call is interrupted by a signal or error. If the call is successful it | |
135 will atomically decrement the semaphore value.</P | |
136 ><P | |
137 >After <TT | |
138 CLASS="FUNCTION" | |
139 >SDL_SemWait()</TT | |
140 > is successful, the semaphore | |
141 can be released and its count atomically incremented by a successful call to | |
142 <A | |
143 HREF="sdlsempost.html" | |
144 >SDL_SemPost</A | |
145 >.</P | |
146 ></DIV | |
147 ><DIV | |
148 CLASS="REFSECT1" | |
149 ><A | |
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150 NAME="AEN8041" |
0 | 151 ></A |
152 ><H2 | |
153 >Return Value</H2 | |
154 ><P | |
155 >Returns <SPAN | |
156 CLASS="RETURNVALUE" | |
157 >0</SPAN | |
158 > if successful or | |
159 <SPAN | |
160 CLASS="RETURNVALUE" | |
161 >-1</SPAN | |
162 > if there was an error (leaving the semaphore unchanged).</P | |
163 ></DIV | |
164 ><DIV | |
165 CLASS="REFSECT1" | |
166 ><A | |
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167 NAME="AEN8046" |
0 | 168 ></A |
169 ><H2 | |
170 >Examples</H2 | |
171 ><P | |
172 ><PRE | |
173 CLASS="PROGRAMLISTING" | |
174 >if (SDL_SemWait(my_sem) == -1) { | |
175 return WAIT_FAILED; | |
176 } | |
177 | |
178 ... | |
179 | |
180 SDL_SemPost(my_sem);</PRE | |
181 ></P | |
182 ></DIV | |
183 ><DIV | |
184 CLASS="REFSECT1" | |
185 ><A | |
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186 NAME="AEN8050" |
0 | 187 ></A |
188 ><H2 | |
189 >See Also</H2 | |
190 ><P | |
191 ><A | |
192 HREF="sdlcreatesemaphore.html" | |
193 ><TT | |
194 CLASS="FUNCTION" | |
195 >SDL_CreateSemaphore</TT | |
196 ></A | |
197 >, | |
198 <A | |
199 HREF="sdldestroysemaphore.html" | |
200 ><TT | |
201 CLASS="FUNCTION" | |
202 >SDL_DestroySemaphore</TT | |
203 ></A | |
204 >, | |
205 <A | |
206 HREF="sdlsemtrywait.html" | |
207 ><TT | |
208 CLASS="FUNCTION" | |
209 >SDL_SemTryWait</TT | |
210 ></A | |
211 >, | |
212 <A | |
213 HREF="sdlsemwaittimeout.html" | |
214 ><TT | |
215 CLASS="FUNCTION" | |
216 >SDL_SemWaitTimeout</TT | |
217 ></A | |
218 >, | |
219 <A | |
220 HREF="sdlsempost.html" | |
221 ><TT | |
222 CLASS="FUNCTION" | |
223 >SDL_SemPost</TT | |
224 ></A | |
225 >, | |
226 <A | |
227 HREF="sdlsemvalue.html" | |
228 ><TT | |
229 CLASS="FUNCTION" | |
230 >SDL_SemValue</TT | |
231 ></A | |
232 ></P | |
233 ></DIV | |
234 ><DIV | |
235 CLASS="NAVFOOTER" | |
236 ><HR | |
237 ALIGN="LEFT" | |
238 WIDTH="100%"><TABLE | |
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239 SUMMARY="Footer navigation table" |
0 | 240 WIDTH="100%" |
241 BORDER="0" | |
242 CELLPADDING="0" | |
243 CELLSPACING="0" | |
244 ><TR | |
245 ><TD | |
246 WIDTH="33%" | |
247 ALIGN="left" | |
248 VALIGN="top" | |
249 ><A | |
250 HREF="sdldestroysemaphore.html" | |
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251 ACCESSKEY="P" |
0 | 252 >Prev</A |
253 ></TD | |
254 ><TD | |
255 WIDTH="34%" | |
256 ALIGN="center" | |
257 VALIGN="top" | |
258 ><A | |
259 HREF="index.html" | |
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260 ACCESSKEY="H" |
0 | 261 >Home</A |
262 ></TD | |
263 ><TD | |
264 WIDTH="33%" | |
265 ALIGN="right" | |
266 VALIGN="top" | |
267 ><A | |
268 HREF="sdlsemtrywait.html" | |
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269 ACCESSKEY="N" |
0 | 270 >Next</A |
271 ></TD | |
272 ></TR | |
273 ><TR | |
274 ><TD | |
275 WIDTH="33%" | |
276 ALIGN="left" | |
277 VALIGN="top" | |
278 >SDL_DestroySemaphore</TD | |
279 ><TD | |
280 WIDTH="34%" | |
281 ALIGN="center" | |
282 VALIGN="top" | |
283 ><A | |
284 HREF="thread.html" | |
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285 ACCESSKEY="U" |
0 | 286 >Up</A |
287 ></TD | |
288 ><TD | |
289 WIDTH="33%" | |
290 ALIGN="right" | |
291 VALIGN="top" | |
292 >SDL_SemTryWait</TD | |
293 ></TR | |
294 ></TABLE | |
295 ></DIV | |
296 ></BODY | |
297 ></HTML | |
298 > |