1 <HTML 2 ><HEAD 3 ><TITLE 4 >SDL_SemTryWait</TITLE 5 ><META 6 NAME="GENERATOR" 7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ 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 SUMMARY="Header navigation table" 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="sdlsemwait.html" 49 ACCESSKEY="P" 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="sdlsemwaittimeout.html" 63 ACCESSKEY="N" 64 >Next</A 65 ></TD 66 ></TR 67 ></TABLE 68 ><HR 69 ALIGN="LEFT" 70 WIDTH="100%"></DIV 71 ><H1 72 ><A 73 NAME="SDLSEMTRYWAIT" 74 ></A 75 >SDL_SemTryWait</H1 76 ><DIV 77 CLASS="REFNAMEDIV" 78 ><A 79 NAME="AEN8069" 80 ></A 81 ><H2 82 >Name</H2 83 >SDL_SemTryWait -- Attempt to lock a semaphore but don't suspend the thread.</DIV 84 ><DIV 85 CLASS="REFSYNOPSISDIV" 86 ><A 87 NAME="AEN8072" 88 ></A 89 ><H2 90 >Synopsis</H2 91 ><DIV 92 CLASS="FUNCSYNOPSIS" 93 ><A 94 NAME="AEN8073" 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_SemTryWait</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 119 NAME="AEN8079" 120 ></A 121 ><H2 122 >Description</H2 123 ><P 124 ><TT 125 CLASS="FUNCTION" 126 >SDL_SemTryWait</TT 127 > is a non-blocking varient of 128 <A 129 HREF="sdlsemwait.html" 130 ><TT 131 CLASS="FUNCTION" 132 >SDL_SemWait</TT 133 ></A 134 >. If the value of the semaphore 135 pointed to by <TT 136 CLASS="PARAMETER" 137 ><I 138 >sem</I 139 ></TT 140 > is positive it will atomically 141 decrement the semaphore value and return 0, otherwise it will return 142 <SPAN 143 CLASS="RETURNVALUE" 144 >SDL_MUTEX_TIMEDOUT</SPAN 145 > instead of suspending the thread.</P 146 ><P 147 >After <TT 148 CLASS="FUNCTION" 149 >SDL_SemTryWait</TT 150 > is successful, the semaphore 151 can be released and its count atomically incremented by a successful call to 152 <A 153 HREF="sdlsempost.html" 154 >SDL_SemPost</A 155 >.</P 156 ></DIV 157 ><DIV 158 CLASS="REFSECT1" 159 ><A 160 NAME="AEN8090" 161 ></A 162 ><H2 163 >Return Value</H2 164 ><P 165 >Returns <SPAN 166 CLASS="RETURNVALUE" 167 >0</SPAN 168 > if the semaphore was successfully locked or 169 either <SPAN 170 CLASS="RETURNVALUE" 171 >SDL_MUTEX_TIMEDOUT</SPAN 172 > or <SPAN 173 CLASS="RETURNVALUE" 174 >-1</SPAN 175 > 176 if the thread would have suspended or there was an error, respectivly.</P 177 ><P 178 >If the semaphore was not successfully locked, the semaphore will be unchanged.</P 179 ></DIV 180 ><DIV 181 CLASS="REFSECT1" 182 ><A 183 NAME="AEN8097" 184 ></A 185 ><H2 186 >Examples</H2 187 ><P 188 ><PRE 189 CLASS="PROGRAMLISTING" 190 >res = SDL_SemTryWait(my_sem); 191 192 if (res == SDL_MUTEX_TIMEDOUT) { 193 return TRY_AGAIN; 194 } 195 if (res == -1) { 196 return WAIT_ERROR; 197 } 198 199 ... 200 201 SDL_SemPost(my_sem);</PRE 202 ></P 203 ></DIV 204 ><DIV 205 CLASS="REFSECT1" 206 ><A 207 NAME="AEN8101" 208 ></A 209 ><H2 210 >See Also</H2 211 ><P 212 ><A 213 HREF="sdlcreatesemaphore.html" 214 ><TT 215 CLASS="FUNCTION" 216 >SDL_CreateSemaphore</TT 217 ></A 218 >, 219 <A 220 HREF="sdldestroysemaphore.html" 221 ><TT 222 CLASS="FUNCTION" 223 >SDL_DestroySemaphore</TT 224 ></A 225 >, 226 <A 227 HREF="sdlsemwait.html" 228 ><TT 229 CLASS="FUNCTION" 230 >SDL_SemWait</TT 231 ></A 232 >, 233 <A 234 HREF="sdlsemwaittimeout.html" 235 ><TT 236 CLASS="FUNCTION" 237 >SDL_SemWaitTimeout</TT 238 ></A 239 >, 240 <A 241 HREF="sdlsempost.html" 242 ><TT 243 CLASS="FUNCTION" 244 >SDL_SemPost</TT 245 ></A 246 >, 247 <A 248 HREF="sdlsemvalue.html" 249 ><TT 250 CLASS="FUNCTION" 251 >SDL_SemValue</TT 252 ></A 253 ></P 254 ></DIV 255 ><DIV 256 CLASS="NAVFOOTER" 257 ><HR 258 ALIGN="LEFT" 259 WIDTH="100%"><TABLE 260 SUMMARY="Footer navigation table" 261 WIDTH="100%" 262 BORDER="0" 263 CELLPADDING="0" 264 CELLSPACING="0" 265 ><TR 266 ><TD 267 WIDTH="33%" 268 ALIGN="left" 269 VALIGN="top" 270 ><A 271 HREF="sdlsemwait.html" 272 ACCESSKEY="P" 273 >Prev</A 274 ></TD 275 ><TD 276 WIDTH="34%" 277 ALIGN="center" 278 VALIGN="top" 279 ><A 280 HREF="index.html" 281 ACCESSKEY="H" 282 >Home</A 283 ></TD 284 ><TD 285 WIDTH="33%" 286 ALIGN="right" 287 VALIGN="top" 288 ><A 289 HREF="sdlsemwaittimeout.html" 290 ACCESSKEY="N" 291 >Next</A 292 ></TD 293 ></TR 294 ><TR 295 ><TD 296 WIDTH="33%" 297 ALIGN="left" 298 VALIGN="top" 299 >SDL_SemWait</TD 300 ><TD 301 WIDTH="34%" 302 ALIGN="center" 303 VALIGN="top" 304 ><A 305 HREF="thread.html" 306 ACCESSKEY="U" 307 >Up</A 308 ></TD 309 ><TD 310 WIDTH="33%" 311 ALIGN="right" 312 VALIGN="top" 313 >SDL_SemWaitTimeout</TD 314 ></TR 315 ></TABLE 316 ></DIV 317 ></BODY 318 ></HTML 319 >
