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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 The following bits may be set in the
64 .Bl -tag -width ".Dv O_CREAT"
66 Create the semaphore if it does not already exist.
68 The third argument to the call to
72 and specifies the mode for the semaphore.
74 .Dv S_IWUSR , S_IWGRP ,
78 it is not possible to grant only
80 permission on a semaphore.
81 The mode is modified according to the process's file creation
85 The fourth argument must be an
87 and specifies the initial value for the semaphore,
88 and must be no greater than
91 Create the semaphore if it does not exist.
92 If the semaphore already exists,
95 This flag is ignored unless
102 function closes a named semaphore that was opened by a call to
107 function removes the semaphore named
109 Resources allocated to the semaphore are only deallocated when all
110 processes that have the semaphore open close it.
115 function returns the address of the opened semaphore.
118 argument is given to multiple calls to
120 by the same process without an intervening call to
122 the same address is returned each time.
123 If the semaphore cannot be opened,
127 and the global variable
129 is set to indicate the error.
131 .Rv -std sem_close sem_unlink
135 function will fail if:
138 The semaphore exists and the permissions specified by
140 at the time it was created deny access to this process.
142 The semaphore does not exist, but permission to create it is denied.
147 are set but the semaphore already exists.
149 The call was interrupted by a signal.
153 operation is not supported for the given
158 argument is greater than
160 .\"FreeBSD never returns EMFILE
162 .\"Too many semaphores are in use by this process.
163 .It Bq Er ENAMETOOLONG
166 argument is too long.
168 The system limit on semaphores has been reached.
171 is set but the named semaphore does not exist.
173 There is not enough space to create the semaphore.
178 function will fail if:
183 argument is not a valid semaphore.
188 function will fail if:
191 Permission is denied to unlink the semaphore.
192 .It Bq Er ENAMETOOLONG
197 The named semaphore does not exist.
218 Support for named semaphores first appeared in
221 This implementation places strict requirements on the value of
223 it must begin with a slash
225 contain no other slash characters,
226 and be less than 14 characters in length
227 not including the terminating null character.