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  1. <HTML
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  4. >SDL_SemTryWait</TITLE
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  16. TITLE="SDL_SemWait"
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  19. TITLE="SDL_SemWaitTimeout"
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  39. >SDL Library Documentation</TH
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  47. HREF="sdlsemwait.html"
  48. >Prev</A
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  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
  76. NAME="AEN7526"
  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
  84. NAME="AEN7529"
  85. ></A
  86. ><H2
  87. >Synopsis</H2
  88. ><DIV
  89. CLASS="FUNCSYNOPSIS"
  90. ><A
  91. NAME="AEN7530"
  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
  116. NAME="AEN7536"
  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
  157. NAME="AEN7547"
  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
  180. NAME="AEN7554"
  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
  204. NAME="AEN7558"
  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
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  292. >SDL_SemWait</TD
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