Mercurial > sdl-ios-xcode
annotate docs/html/sdlsemwait.html @ 765:4c2ba6161939
Editors Note: The original patch was modified to use SDL_Delay() instead of
nanosleep because nanosleep may not be portable to all systems
using SDL with the ALSA backend. This may be a moot point with
the switch to blocking writes anyway...
Date: Sat, 27 Dec 2003 21:47:36 +0100
From: Michel Daenzer
To: Debian Bug Tracking System
Subject: [SDL] Bug#225252: [PATCH] ALSA fixes
Package: libsdl1.2debian-all
Version: 1.2.6-2
Severity: normal
Tags: patch
For SDL 1.2.6, the ALSA backend was changed to call snd_pcm_open() with
SND_PCM_NONBLOCK. That's a good idea per se, however, it causes high CPU
usage, interrupted sound and stuttering in some games here. Taking a nanosleep
whenever snd_pcm_writei() returns -EAGAIN fixes this, but I think it's more
efficient to use blocking mode for the actual sound playback. Feedback from the
SDL and ALSA lists appreciated.
The patch also fixes the default ALSA device to be used.
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Sun, 04 Jan 2004 15:40:50 +0000 |
| parents | e5bc29de3f0a |
| children | 355632dca928 |
| rev | line source |
|---|---|
| 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 1.64 |
| 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_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 | |
| 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="sdldestroysemaphore.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="sdlsemtrywait.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="SDLSEMWAIT" | |
| 71 >SDL_SemWait</A | |
| 72 ></H1 | |
| 73 ><DIV | |
| 74 CLASS="REFNAMEDIV" | |
| 75 ><A | |
|
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76 NAME="AEN7635" |
| 0 | 77 ></A |
| 78 ><H2 | |
| 79 >Name</H2 | |
| 80 >SDL_SemWait -- Lock a semaphore and suspend the thread if the semaphore value is zero.</DIV | |
| 81 ><DIV | |
| 82 CLASS="REFSYNOPSISDIV" | |
| 83 ><A | |
|
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84 NAME="AEN7638" |
| 0 | 85 ></A |
| 86 ><H2 | |
| 87 >Synopsis</H2 | |
| 88 ><DIV | |
| 89 CLASS="FUNCSYNOPSIS" | |
| 90 ><A | |
|
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91 NAME="AEN7639" |
| 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_SemWait</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 | |
|
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116 NAME="AEN7645" |
| 0 | 117 ></A |
| 118 ><H2 | |
| 119 >Description</H2 | |
| 120 ><P | |
| 121 ><TT | |
| 122 CLASS="FUNCTION" | |
| 123 >SDL_SemWait()</TT | |
| 124 > suspends the calling thread until either | |
| 125 the semaphore pointed to by <TT | |
| 126 CLASS="PARAMETER" | |
| 127 ><I | |
| 128 >sem</I | |
| 129 ></TT | |
| 130 > has a positive value, | |
| 131 the call is interrupted by a signal or error. If the call is successful it | |
| 132 will atomically decrement the semaphore value.</P | |
| 133 ><P | |
| 134 >After <TT | |
| 135 CLASS="FUNCTION" | |
| 136 >SDL_SemWait()</TT | |
| 137 > is successful, the semaphore | |
| 138 can be released and its count atomically incremented by a successful call to | |
| 139 <A | |
| 140 HREF="sdlsempost.html" | |
| 141 >SDL_SemPost</A | |
| 142 >.</P | |
| 143 ></DIV | |
| 144 ><DIV | |
| 145 CLASS="REFSECT1" | |
| 146 ><A | |
|
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147 NAME="AEN7653" |
| 0 | 148 ></A |
| 149 ><H2 | |
| 150 >Return Value</H2 | |
| 151 ><P | |
| 152 >Returns <SPAN | |
| 153 CLASS="RETURNVALUE" | |
| 154 >0</SPAN | |
| 155 > if successful or | |
| 156 <SPAN | |
| 157 CLASS="RETURNVALUE" | |
| 158 >-1</SPAN | |
| 159 > if there was an error (leaving the semaphore unchanged).</P | |
| 160 ></DIV | |
| 161 ><DIV | |
| 162 CLASS="REFSECT1" | |
| 163 ><A | |
|
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164 NAME="AEN7658" |
| 0 | 165 ></A |
| 166 ><H2 | |
| 167 >Examples</H2 | |
| 168 ><P | |
| 169 ><PRE | |
| 170 CLASS="PROGRAMLISTING" | |
| 171 >if (SDL_SemWait(my_sem) == -1) { | |
| 172 return WAIT_FAILED; | |
| 173 } | |
| 174 | |
| 175 ... | |
| 176 | |
| 177 SDL_SemPost(my_sem);</PRE | |
| 178 ></P | |
| 179 ></DIV | |
| 180 ><DIV | |
| 181 CLASS="REFSECT1" | |
| 182 ><A | |
|
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183 NAME="AEN7662" |
| 0 | 184 ></A |
| 185 ><H2 | |
| 186 >See Also</H2 | |
| 187 ><P | |
| 188 ><A | |
| 189 HREF="sdlcreatesemaphore.html" | |
| 190 ><TT | |
| 191 CLASS="FUNCTION" | |
| 192 >SDL_CreateSemaphore</TT | |
| 193 ></A | |
| 194 >, | |
| 195 <A | |
| 196 HREF="sdldestroysemaphore.html" | |
| 197 ><TT | |
| 198 CLASS="FUNCTION" | |
| 199 >SDL_DestroySemaphore</TT | |
| 200 ></A | |
| 201 >, | |
| 202 <A | |
| 203 HREF="sdlsemtrywait.html" | |
| 204 ><TT | |
| 205 CLASS="FUNCTION" | |
| 206 >SDL_SemTryWait</TT | |
| 207 ></A | |
| 208 >, | |
| 209 <A | |
| 210 HREF="sdlsemwaittimeout.html" | |
| 211 ><TT | |
| 212 CLASS="FUNCTION" | |
| 213 >SDL_SemWaitTimeout</TT | |
| 214 ></A | |
| 215 >, | |
| 216 <A | |
| 217 HREF="sdlsempost.html" | |
| 218 ><TT | |
| 219 CLASS="FUNCTION" | |
| 220 >SDL_SemPost</TT | |
| 221 ></A | |
| 222 >, | |
| 223 <A | |
| 224 HREF="sdlsemvalue.html" | |
| 225 ><TT | |
| 226 CLASS="FUNCTION" | |
| 227 >SDL_SemValue</TT | |
| 228 ></A | |
| 229 ></P | |
| 230 ></DIV | |
| 231 ><DIV | |
| 232 CLASS="NAVFOOTER" | |
| 233 ><HR | |
| 234 ALIGN="LEFT" | |
| 235 WIDTH="100%"><TABLE | |
| 236 WIDTH="100%" | |
| 237 BORDER="0" | |
| 238 CELLPADDING="0" | |
| 239 CELLSPACING="0" | |
| 240 ><TR | |
| 241 ><TD | |
| 242 WIDTH="33%" | |
| 243 ALIGN="left" | |
| 244 VALIGN="top" | |
| 245 ><A | |
| 246 HREF="sdldestroysemaphore.html" | |
| 247 >Prev</A | |
| 248 ></TD | |
| 249 ><TD | |
| 250 WIDTH="34%" | |
| 251 ALIGN="center" | |
| 252 VALIGN="top" | |
| 253 ><A | |
| 254 HREF="index.html" | |
| 255 >Home</A | |
| 256 ></TD | |
| 257 ><TD | |
| 258 WIDTH="33%" | |
| 259 ALIGN="right" | |
| 260 VALIGN="top" | |
| 261 ><A | |
| 262 HREF="sdlsemtrywait.html" | |
| 263 >Next</A | |
| 264 ></TD | |
| 265 ></TR | |
| 266 ><TR | |
| 267 ><TD | |
| 268 WIDTH="33%" | |
| 269 ALIGN="left" | |
| 270 VALIGN="top" | |
| 271 >SDL_DestroySemaphore</TD | |
| 272 ><TD | |
| 273 WIDTH="34%" | |
| 274 ALIGN="center" | |
| 275 VALIGN="top" | |
| 276 ><A | |
| 277 HREF="thread.html" | |
| 278 >Up</A | |
| 279 ></TD | |
| 280 ><TD | |
| 281 WIDTH="33%" | |
| 282 ALIGN="right" | |
| 283 VALIGN="top" | |
| 284 >SDL_SemTryWait</TD | |
| 285 ></TR | |
| 286 ></TABLE | |
| 287 ></DIV | |
| 288 ></BODY | |
| 289 ></HTML | |
| 290 > |