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4>SDL_CreateSemaphore</TITLE
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71><H1
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75>SDL_CreateSemaphore</H1
76><DIV
77CLASS="REFNAMEDIV"
78><A
79NAME="AEN7936"
80></A
81><H2
82>Name</H2
83>SDL_CreateSemaphore&nbsp;--&nbsp;Creates a new semaphore and assigns an initial value to it.</DIV
84><DIV
85CLASS="REFSYNOPSISDIV"
86><A
87NAME="AEN7939"
88></A
89><H2
90>Synopsis</H2
91><DIV
92CLASS="FUNCSYNOPSIS"
93><A
94NAME="AEN7940"
95></A
96><P
97></P
98><PRE
99CLASS="FUNCSYNOPSISINFO"
100>#include "SDL.h"
101#include "SDL_thread.h"</PRE
102><P
103><CODE
104><CODE
105CLASS="FUNCDEF"
106>SDL_sem *<B
107CLASS="FSFUNC"
108>SDL_CreateSemaphore</B
109></CODE
110>(Uint32 initial_value);</CODE
111></P
112><P
113></P
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116><DIV
117CLASS="REFSECT1"
118><A
119NAME="AEN7946"
120></A
121><H2
122>Description</H2
123><P
124><TT
125CLASS="FUNCTION"
126>SDL_CreateSemaphore()</TT
127> creates a new semaphore and
128initializes it with the value <TT
129CLASS="PARAMETER"
130><I
131>initial_value</I
132></TT
133>.
134Each locking operation on the semaphore by
135<A
136HREF="sdlsemwait.html"
137>SDL_SemWait</A
138>,
139<A
140HREF="sdlsemtrywait.html"
141>SDL_SemTryWait</A
142> or
143<A
144HREF="sdlsemwaittimeout.html"
145>SDL_SemWaitTimeout</A
146>
147will atomically decrement the semaphore value. The locking operation will be blocked
148if the semaphore value is not positive (greater than zero). Each unlock operation by
149<A
150HREF="sdlsempost.html"
151>SDL_SemPost</A
152>
153will atomically increment the semaphore value.</P
154></DIV
155><DIV
156CLASS="REFSECT1"
157><A
158NAME="AEN7955"
159></A
160><H2
161>Return Value</H2
162><P
163>Returns a pointer to an initialized semaphore or
164<SPAN
165CLASS="RETURNVALUE"
166>NULL</SPAN
167> if there was an error.</P
168></DIV
169><DIV
170CLASS="REFSECT1"
171><A
172NAME="AEN7959"
173></A
174><H2
175>Examples</H2
176><P
177><PRE
178CLASS="PROGRAMLISTING"
179>SDL_sem *my_sem;
180
181my_sem = SDL_CreateSemaphore(INITIAL_SEM_VALUE);
182
183if (my_sem == NULL) {
184        return CREATE_SEM_FAILED;
185}</PRE
186></P
187></DIV
188><DIV
189CLASS="REFSECT1"
190><A
191NAME="AEN7963"
192></A
193><H2
194>See Also</H2
195><P
196><A
197HREF="sdldestroysemaphore.html"
198><TT
199CLASS="FUNCTION"
200>SDL_DestroySemaphore</TT
201></A
202>,
203<A
204HREF="sdlsemwait.html"
205><TT
206CLASS="FUNCTION"
207>SDL_SemWait</TT
208></A
209>,
210<A
211HREF="sdlsemtrywait.html"
212><TT
213CLASS="FUNCTION"
214>SDL_SemTryWait</TT
215></A
216>,
217<A
218HREF="sdlsemwaittimeout.html"
219><TT
220CLASS="FUNCTION"
221>SDL_SemWaitTimeout</TT
222></A
223>,
224<A
225HREF="sdlsempost.html"
226><TT
227CLASS="FUNCTION"
228>SDL_SemPost</TT
229></A
230>,
231<A
232HREF="sdlsemvalue.html"
233><TT
234CLASS="FUNCTION"
235>SDL_SemValue</TT
236></A
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