| 1 | <HTML |
| 2 | ><HEAD |
| 3 | ><TITLE |
| 4 | >SDL_SemWait</TITLE |
| 5 | ><META |
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| 7 | CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ |
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| 10 | TITLE="SDL Library Documentation" |
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| 13 | TITLE="Multi-threaded Programming" |
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| 16 | TITLE="SDL_DestroySemaphore" |
| 17 | HREF="sdldestroysemaphore.html"><LINK |
| 18 | REL="NEXT" |
| 19 | TITLE="SDL_SemTryWait" |
| 20 | HREF="sdlsemtrywait.html"></HEAD |
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| 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" |
| 49 | ACCESSKEY="P" |
| 50 | >Prev</A |
| 51 | ></TD |
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| 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" |
| 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="SDLSEMWAIT" |
| 74 | ></A |
| 75 | >SDL_SemWait</H1 |
| 76 | ><DIV |
| 77 | CLASS="REFNAMEDIV" |
| 78 | ><A |
| 79 | NAME="AEN8023" |
| 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 |
| 87 | NAME="AEN8026" |
| 88 | ></A |
| 89 | ><H2 |
| 90 | >Synopsis</H2 |
| 91 | ><DIV |
| 92 | CLASS="FUNCSYNOPSIS" |
| 93 | ><A |
| 94 | NAME="AEN8027" |
| 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 |
| 119 | NAME="AEN8033" |
| 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 |
| 150 | NAME="AEN8041" |
| 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 |
| 167 | NAME="AEN8046" |
| 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 |
| 186 | NAME="AEN8050" |
| 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 |
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| 246 | WIDTH="33%" |
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| 248 | VALIGN="top" |
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| 250 | HREF="sdldestroysemaphore.html" |
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| 252 | >Prev</A |
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| 263 | ><TD |
| 264 | WIDTH="33%" |
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| 266 | VALIGN="top" |
| 267 | ><A |
| 268 | HREF="sdlsemtrywait.html" |
| 269 | ACCESSKEY="N" |
| 270 | >Next</A |
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| 277 | VALIGN="top" |
| 278 | >SDL_DestroySemaphore</TD |
| 279 | ><TD |
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| 292 | >SDL_SemTryWait</TD |
| 293 | ></TR |
| 294 | ></TABLE |
| 295 | ></DIV |
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| 297 | ></HTML |
| 298 | > |