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37 .Nd named semaphore operations
43 .Fn sem_open "const char *name" "int oflag" ...
45 .Fn sem_close "sem_t *sem"
47 .Fn sem_unlink "const char *name"
51 function creates or opens the named semaphore specified by
53 The returned semaphore may be used in subsequent calls to
61 This implementation places strict requirements on the value of
63 it must begin with a slash
65 and contain no other slash characters.
67 The following bits may be set in the
70 .Bl -tag -width ".Dv O_CREAT"
72 Create the semaphore if it does not already exist.
74 The third argument to the call to
78 and specifies the mode for the semaphore.
80 .Dv S_IWUSR , S_IWGRP ,
84 it is not possible to grant only
86 permission on a semaphore.
87 The mode is modified according to the process's file creation
91 The fourth argument must be an
93 and specifies the initial value for the semaphore,
94 and must be no greater than
97 Create the semaphore if it does not exist.
98 If the semaphore already exists,
101 This flag is ignored unless
108 function closes a named semaphore that was opened by a call to
113 function removes the semaphore named
115 Resources allocated to the semaphore are only deallocated when all
116 processes that have the semaphore open close it.
121 function returns the address of the opened semaphore.
124 argument is given to multiple calls to
126 by the same process without an intervening call to
128 the same address is returned each time.
129 If the semaphore cannot be opened,
133 and the global variable
135 is set to indicate the error.
137 .Rv -std sem_close sem_unlink
141 function will fail if:
144 The semaphore exists and the permissions specified by
146 at the time it was created deny access to this process.
148 The semaphore does not exist, but permission to create it is denied.
153 are set but the semaphore already exists.
155 The call was interrupted by a signal.
159 operation is not supported for the given
164 argument is greater than
166 .\"FreeBSD never returns EMFILE
168 .\"Too many semaphores are in use by this process.
169 .It Bq Er ENAMETOOLONG
172 argument is too long.
174 The system limit on semaphores has been reached.
177 is not set but the named semaphore does not exist.
179 There is not enough space to create the semaphore.
184 function will fail if:
189 argument is not a valid semaphore.
194 function will fail if:
197 Permission is denied to unlink the semaphore.
198 .It Bq Er ENAMETOOLONG
203 The named semaphore does not exist.
224 Support for named semaphores first appeared in