Mercurial > sdl-ios-xcode
annotate docs/html/sdlcreatesemaphore.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_CreateSemaphore</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_mutexV" | |
| 17 HREF="sdlmutexv.html"><LINK | |
| 18 REL="NEXT" | |
| 19 TITLE="SDL_DestroySemaphore" | |
| 20 HREF="sdldestroysemaphore.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="sdlmutexv.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="sdldestroysemaphore.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="SDLCREATESEMAPHORE" | |
| 71 >SDL_CreateSemaphore</A | |
| 72 ></H1 | |
| 73 ><DIV | |
| 74 CLASS="REFNAMEDIV" | |
| 75 ><A | |
|
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76 NAME="AEN7548" |
| 0 | 77 ></A |
| 78 ><H2 | |
| 79 >Name</H2 | |
| 80 >SDL_CreateSemaphore -- Creates a new semaphore and assigns an initial value to it.</DIV | |
| 81 ><DIV | |
| 82 CLASS="REFSYNOPSISDIV" | |
| 83 ><A | |
|
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84 NAME="AEN7551" |
| 0 | 85 ></A |
| 86 ><H2 | |
| 87 >Synopsis</H2 | |
| 88 ><DIV | |
| 89 CLASS="FUNCSYNOPSIS" | |
| 90 ><A | |
|
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91 NAME="AEN7552" |
| 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 >SDL_sem *<B | |
| 104 CLASS="FSFUNC" | |
| 105 >SDL_CreateSemaphore</B | |
| 106 ></CODE | |
| 107 >(Uint32 initial_value);</CODE | |
| 108 ></P | |
| 109 ><P | |
| 110 ></P | |
| 111 ></DIV | |
| 112 ></DIV | |
| 113 ><DIV | |
| 114 CLASS="REFSECT1" | |
| 115 ><A | |
|
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116 NAME="AEN7558" |
| 0 | 117 ></A |
| 118 ><H2 | |
| 119 >Description</H2 | |
| 120 ><P | |
| 121 ><TT | |
| 122 CLASS="FUNCTION" | |
| 123 >SDL_CreateSemaphore()</TT | |
| 124 > creates a new semaphore and | |
| 125 initializes it with the value <TT | |
| 126 CLASS="PARAMETER" | |
| 127 ><I | |
| 128 >initial_value</I | |
| 129 ></TT | |
| 130 >. | |
| 131 Each locking operation on the semaphore by | |
| 132 <A | |
| 133 HREF="sdlsemwait.html" | |
| 134 >SDL_SemWait</A | |
| 135 >, | |
| 136 <A | |
| 137 HREF="sdlsemtrywait.html" | |
| 138 >SDL_SemTryWait</A | |
| 139 > or | |
| 140 <A | |
| 141 HREF="sdlsemwaittimeout.html" | |
| 142 >SDL_SemWaitTimeout</A | |
| 143 > | |
| 144 will atomically decrement the semaphore value. The locking operation will be blocked | |
| 145 if the semaphore value is not positive (greater than zero). Each unlock operation by | |
| 146 <A | |
| 147 HREF="sdlsempost.html" | |
| 148 >SDL_SemPost</A | |
| 149 > | |
| 150 will atomically increment the semaphore value.</P | |
| 151 ></DIV | |
| 152 ><DIV | |
| 153 CLASS="REFSECT1" | |
| 154 ><A | |
|
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155 NAME="AEN7567" |
| 0 | 156 ></A |
| 157 ><H2 | |
| 158 >Return Value</H2 | |
| 159 ><P | |
| 160 >Returns a pointer to an initialized semaphore or | |
| 161 <SPAN | |
| 162 CLASS="RETURNVALUE" | |
| 163 >NULL</SPAN | |
| 164 > if there was an error.</P | |
| 165 ></DIV | |
| 166 ><DIV | |
| 167 CLASS="REFSECT1" | |
| 168 ><A | |
|
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169 NAME="AEN7571" |
| 0 | 170 ></A |
| 171 ><H2 | |
| 172 >Examples</H2 | |
| 173 ><P | |
| 174 ><PRE | |
| 175 CLASS="PROGRAMLISTING" | |
| 176 >SDL_sem *my_sem; | |
| 177 | |
| 178 my_sem = SDL_CreateSemaphore(INITIAL_SEM_VALUE); | |
| 179 | |
| 180 if (my_sem == NULL) { | |
| 181 return CREATE_SEM_FAILED; | |
| 182 }</PRE | |
| 183 ></P | |
| 184 ></DIV | |
| 185 ><DIV | |
| 186 CLASS="REFSECT1" | |
| 187 ><A | |
|
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188 NAME="AEN7575" |
| 0 | 189 ></A |
| 190 ><H2 | |
| 191 >See Also</H2 | |
| 192 ><P | |
| 193 ><A | |
| 194 HREF="sdldestroysemaphore.html" | |
| 195 ><TT | |
| 196 CLASS="FUNCTION" | |
| 197 >SDL_DestroySemaphore</TT | |
| 198 ></A | |
| 199 >, | |
| 200 <A | |
| 201 HREF="sdlsemwait.html" | |
| 202 ><TT | |
| 203 CLASS="FUNCTION" | |
| 204 >SDL_SemWait</TT | |
| 205 ></A | |
| 206 >, | |
| 207 <A | |
| 208 HREF="sdlsemtrywait.html" | |
| 209 ><TT | |
| 210 CLASS="FUNCTION" | |
| 211 >SDL_SemTryWait</TT | |
| 212 ></A | |
| 213 >, | |
| 214 <A | |
| 215 HREF="sdlsemwaittimeout.html" | |
| 216 ><TT | |
| 217 CLASS="FUNCTION" | |
| 218 >SDL_SemWaitTimeout</TT | |
| 219 ></A | |
| 220 >, | |
| 221 <A | |
| 222 HREF="sdlsempost.html" | |
| 223 ><TT | |
| 224 CLASS="FUNCTION" | |
| 225 >SDL_SemPost</TT | |
| 226 ></A | |
| 227 >, | |
| 228 <A | |
| 229 HREF="sdlsemvalue.html" | |
| 230 ><TT | |
| 231 CLASS="FUNCTION" | |
| 232 >SDL_SemValue</TT | |
| 233 ></A | |
| 234 ></P | |
| 235 ></DIV | |
| 236 ><DIV | |
| 237 CLASS="NAVFOOTER" | |
| 238 ><HR | |
| 239 ALIGN="LEFT" | |
| 240 WIDTH="100%"><TABLE | |
| 241 WIDTH="100%" | |
| 242 BORDER="0" | |
| 243 CELLPADDING="0" | |
| 244 CELLSPACING="0" | |
| 245 ><TR | |
| 246 ><TD | |
| 247 WIDTH="33%" | |
| 248 ALIGN="left" | |
| 249 VALIGN="top" | |
| 250 ><A | |
| 251 HREF="sdlmutexv.html" | |
| 252 >Prev</A | |
| 253 ></TD | |
| 254 ><TD | |
| 255 WIDTH="34%" | |
| 256 ALIGN="center" | |
| 257 VALIGN="top" | |
| 258 ><A | |
| 259 HREF="index.html" | |
| 260 >Home</A | |
| 261 ></TD | |
| 262 ><TD | |
| 263 WIDTH="33%" | |
| 264 ALIGN="right" | |
| 265 VALIGN="top" | |
| 266 ><A | |
| 267 HREF="sdldestroysemaphore.html" | |
| 268 >Next</A | |
| 269 ></TD | |
| 270 ></TR | |
| 271 ><TR | |
| 272 ><TD | |
| 273 WIDTH="33%" | |
| 274 ALIGN="left" | |
| 275 VALIGN="top" | |
| 276 >SDL_mutexV</TD | |
| 277 ><TD | |
| 278 WIDTH="34%" | |
| 279 ALIGN="center" | |
| 280 VALIGN="top" | |
| 281 ><A | |
| 282 HREF="thread.html" | |
| 283 >Up</A | |
| 284 ></TD | |
| 285 ><TD | |
| 286 WIDTH="33%" | |
| 287 ALIGN="right" | |
| 288 VALIGN="top" | |
| 289 >SDL_DestroySemaphore</TD | |
| 290 ></TR | |
| 291 ></TABLE | |
| 292 ></DIV | |
| 293 ></BODY | |
| 294 ></HTML | |
| 295 > |