Mercurial > sdl-ios-xcode
annotate docs/html/sdlsemtrywait.html @ 773:da0a2ad35bf4
Date: Sun, 4 Jan 2004 23:48:19 +0100
From: Max Horn
Subject: Re: Again Audio CD patch
Am 04.01.2004 um 22:38 schrieb Sam Lantinga:
>
> Okay, I fixed the buffering problems by simply using a 4 second buffer
> instead of a 1 second buffer. However, using your code I can't play an
> entire CD - the playback stops after the first song.
>
Found the problem: FSReadFork returns eofErr when the file is finished.
However, we check its return value for errors, and if anything but
noErr occurs, the reader thread aborts its current iteration. That is
bad, because it aborts before it can ever set the flag which tells that
the file is over (also, any remaining data which FSRead did return is
lost - so you'd not hear about to 4 seconds from the end of the file.
Furthermore, the computed data size was 8 bytes to high (I forgot to
account for the fact that the size of an (A)IFF chunk always contains
the chunk header & size fields, too). This is enough to make it work.
However, the end condition is rather fragile, so I tuned some other
things to be pessimistic (check for <= 0 instead of == 0, when eofErr
is encountered enforce mReadFilePosition == mFileLength). You never
know...
The attached patch fixes the issue for me.
author | Sam Lantinga <slouken@libsdl.org> |
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date | Mon, 05 Jan 2004 00:57:51 +0000 |
parents | e5bc29de3f0a |
children | 355632dca928 |
rev | line source |
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0 | 1 <HTML |
2 ><HEAD | |
3 ><TITLE | |
4 >SDL_SemTryWait</TITLE | |
5 ><META | |
6 NAME="GENERATOR" | |
55
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.64 |
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_SemWait" | |
17 HREF="sdlsemwait.html"><LINK | |
18 REL="NEXT" | |
19 TITLE="SDL_SemWaitTimeout" | |
20 HREF="sdlsemwaittimeout.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 | |
31 WIDTH="100%" | |
32 BORDER="0" | |
33 CELLPADDING="0" | |
34 CELLSPACING="0" | |
35 ><TR | |
36 ><TH | |
37 COLSPAN="3" | |
38 ALIGN="center" | |
39 >SDL Library Documentation</TH | |
40 ></TR | |
41 ><TR | |
42 ><TD | |
43 WIDTH="10%" | |
44 ALIGN="left" | |
45 VALIGN="bottom" | |
46 ><A | |
47 HREF="sdlsemwait.html" | |
48 >Prev</A | |
49 ></TD | |
50 ><TD | |
51 WIDTH="80%" | |
52 ALIGN="center" | |
53 VALIGN="bottom" | |
54 ></TD | |
55 ><TD | |
56 WIDTH="10%" | |
57 ALIGN="right" | |
58 VALIGN="bottom" | |
59 ><A | |
60 HREF="sdlsemwaittimeout.html" | |
61 >Next</A | |
62 ></TD | |
63 ></TR | |
64 ></TABLE | |
65 ><HR | |
66 ALIGN="LEFT" | |
67 WIDTH="100%"></DIV | |
68 ><H1 | |
69 ><A | |
70 NAME="SDLSEMTRYWAIT" | |
71 >SDL_SemTryWait</A | |
72 ></H1 | |
73 ><DIV | |
74 CLASS="REFNAMEDIV" | |
75 ><A | |
181
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76 NAME="AEN7681" |
0 | 77 ></A |
78 ><H2 | |
79 >Name</H2 | |
80 >SDL_SemTryWait -- Attempt to lock a semaphore but don't suspend the thread.</DIV | |
81 ><DIV | |
82 CLASS="REFSYNOPSISDIV" | |
83 ><A | |
181
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84 NAME="AEN7684" |
0 | 85 ></A |
86 ><H2 | |
87 >Synopsis</H2 | |
88 ><DIV | |
89 CLASS="FUNCSYNOPSIS" | |
90 ><A | |
181
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91 NAME="AEN7685" |
0 | 92 ></A |
93 ><P | |
94 ></P | |
95 ><PRE | |
96 CLASS="FUNCSYNOPSISINFO" | |
97 >#include "SDL.h" | |
98 #include "SDL_thread.h"</PRE | |
99 ><P | |
100 ><CODE | |
101 ><CODE | |
102 CLASS="FUNCDEF" | |
103 >int <B | |
104 CLASS="FSFUNC" | |
105 >SDL_SemTryWait</B | |
106 ></CODE | |
107 >(SDL_sem *sem);</CODE | |
108 ></P | |
109 ><P | |
110 ></P | |
111 ></DIV | |
112 ></DIV | |
113 ><DIV | |
114 CLASS="REFSECT1" | |
115 ><A | |
181
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116 NAME="AEN7691" |
0 | 117 ></A |
118 ><H2 | |
119 >Description</H2 | |
120 ><P | |
121 ><TT | |
122 CLASS="FUNCTION" | |
123 >SDL_SemTryWait</TT | |
124 > is a non-blocking varient of | |
125 <A | |
126 HREF="sdlsemwait.html" | |
127 ><TT | |
128 CLASS="FUNCTION" | |
129 >SDL_SemWait</TT | |
130 ></A | |
131 >. If the value of the semaphore | |
132 pointed to by <TT | |
133 CLASS="PARAMETER" | |
134 ><I | |
135 >sem</I | |
136 ></TT | |
137 > is positive it will atomically | |
138 decrement the semaphore value and return 0, otherwise it will return | |
139 <SPAN | |
140 CLASS="RETURNVALUE" | |
141 >SDL_MUTEX_TIMEOUT</SPAN | |
142 > instead of suspending the thread.</P | |
143 ><P | |
144 >After <TT | |
145 CLASS="FUNCTION" | |
146 >SDL_SemTryWait</TT | |
147 > is successful, the semaphore | |
148 can be released and its count atomically incremented by a successful call to | |
149 <A | |
150 HREF="sdlsempost.html" | |
151 >SDL_SemPost</A | |
152 >.</P | |
153 ></DIV | |
154 ><DIV | |
155 CLASS="REFSECT1" | |
156 ><A | |
181
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157 NAME="AEN7702" |
0 | 158 ></A |
159 ><H2 | |
160 >Return Value</H2 | |
161 ><P | |
162 >Returns <SPAN | |
163 CLASS="RETURNVALUE" | |
164 >0</SPAN | |
165 > if the semaphore was successfully locked or | |
166 either <SPAN | |
167 CLASS="RETURNVALUE" | |
168 >SDL_MUTEX_TIMEOUT</SPAN | |
169 > or <SPAN | |
170 CLASS="RETURNVALUE" | |
171 >-1</SPAN | |
172 > | |
173 if the thread would have suspended or there was an error, respectivly.</P | |
174 ><P | |
175 >If the semaphore was not successfully locked, the semaphore will be unchanged.</P | |
176 ></DIV | |
177 ><DIV | |
178 CLASS="REFSECT1" | |
179 ><A | |
181
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180 NAME="AEN7709" |
0 | 181 ></A |
182 ><H2 | |
183 >Examples</H2 | |
184 ><P | |
185 ><PRE | |
186 CLASS="PROGRAMLISTING" | |
187 >res = SDL_SemTryWait(my_sem); | |
188 | |
189 if (res == SDL_MUTEX_TIMEOUT) { | |
190 return TRY_AGAIN; | |
191 } | |
192 if (res == -1) { | |
193 return WAIT_ERROR; | |
194 } | |
195 | |
196 ... | |
197 | |
198 SDL_SemPost(my_sem);</PRE | |
199 ></P | |
200 ></DIV | |
201 ><DIV | |
202 CLASS="REFSECT1" | |
203 ><A | |
181
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204 NAME="AEN7713" |
0 | 205 ></A |
206 ><H2 | |
207 >See Also</H2 | |
208 ><P | |
209 ><A | |
210 HREF="sdlcreatesemaphore.html" | |
211 ><TT | |
212 CLASS="FUNCTION" | |
213 >SDL_CreateSemaphore</TT | |
214 ></A | |
215 >, | |
216 <A | |
217 HREF="sdldestroysemaphore.html" | |
218 ><TT | |
219 CLASS="FUNCTION" | |
220 >SDL_DestroySemaphore</TT | |
221 ></A | |
222 >, | |
223 <A | |
224 HREF="sdlsemwait.html" | |
225 ><TT | |
226 CLASS="FUNCTION" | |
227 >SDL_SemWait</TT | |
228 ></A | |
229 >, | |
230 <A | |
231 HREF="sdlsemwaittimeout.html" | |
232 ><TT | |
233 CLASS="FUNCTION" | |
234 >SDL_SemWaitTimeout</TT | |
235 ></A | |
236 >, | |
237 <A | |
238 HREF="sdlsempost.html" | |
239 ><TT | |
240 CLASS="FUNCTION" | |
241 >SDL_SemPost</TT | |
242 ></A | |
243 >, | |
244 <A | |
245 HREF="sdlsemvalue.html" | |
246 ><TT | |
247 CLASS="FUNCTION" | |
248 >SDL_SemValue</TT | |
249 ></A | |
250 ></P | |
251 ></DIV | |
252 ><DIV | |
253 CLASS="NAVFOOTER" | |
254 ><HR | |
255 ALIGN="LEFT" | |
256 WIDTH="100%"><TABLE | |
257 WIDTH="100%" | |
258 BORDER="0" | |
259 CELLPADDING="0" | |
260 CELLSPACING="0" | |
261 ><TR | |
262 ><TD | |
263 WIDTH="33%" | |
264 ALIGN="left" | |
265 VALIGN="top" | |
266 ><A | |
267 HREF="sdlsemwait.html" | |
268 >Prev</A | |
269 ></TD | |
270 ><TD | |
271 WIDTH="34%" | |
272 ALIGN="center" | |
273 VALIGN="top" | |
274 ><A | |
275 HREF="index.html" | |
276 >Home</A | |
277 ></TD | |
278 ><TD | |
279 WIDTH="33%" | |
280 ALIGN="right" | |
281 VALIGN="top" | |
282 ><A | |
283 HREF="sdlsemwaittimeout.html" | |
284 >Next</A | |
285 ></TD | |
286 ></TR | |
287 ><TR | |
288 ><TD | |
289 WIDTH="33%" | |
290 ALIGN="left" | |
291 VALIGN="top" | |
292 >SDL_SemWait</TD | |
293 ><TD | |
294 WIDTH="34%" | |
295 ALIGN="center" | |
296 VALIGN="top" | |
297 ><A | |
298 HREF="thread.html" | |
299 >Up</A | |
300 ></TD | |
301 ><TD | |
302 WIDTH="33%" | |
303 ALIGN="right" | |
304 VALIGN="top" | |
305 >SDL_SemWaitTimeout</TD | |
306 ></TR | |
307 ></TABLE | |
308 ></DIV | |
309 ></BODY | |
310 ></HTML | |
311 > |