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35 .Nd named semaphore operations
41 .Fn sem_open "const char *name" "int oflag" ...
43 .Fn sem_close "sem_t *sem"
45 .Fn sem_unlink "const char *name"
49 function creates or opens the named semaphore specified by
51 The returned semaphore may be used in subsequent calls to
59 This implementation places strict requirements on the value of
61 it must begin with a slash
63 and contain no other slash characters.
65 The following bits may be set in the
68 .Bl -tag -width ".Dv O_CREAT"
70 Create the semaphore if it does not already exist.
72 The third argument to the call to
76 and specifies the mode for the semaphore.
78 .Dv S_IWUSR , S_IWGRP ,
82 it is not possible to grant only
84 permission on a semaphore.
85 The mode is modified according to the process's file creation
89 The fourth argument must be an
91 and specifies the initial value for the semaphore,
92 and must be no greater than
95 Create the semaphore if it does not exist.
96 If the semaphore already exists,
99 This flag is ignored unless
106 function closes a named semaphore that was opened by a call to
111 function removes the semaphore named
113 Resources allocated to the semaphore are only deallocated when all
114 processes that have the semaphore open close it.
119 function returns the address of the opened semaphore.
122 argument is given to multiple calls to
124 by the same process without an intervening call to
126 the same address is returned each time.
127 If the semaphore cannot be opened,
131 and the global variable
133 is set to indicate the error.
135 .Rv -std sem_close sem_unlink
139 function will fail if:
142 The semaphore exists and the permissions specified by
144 at the time it was created deny access to this process.
146 The semaphore does not exist, but permission to create it is denied.
151 are set but the semaphore already exists.
153 The call was interrupted by a signal.
157 operation is not supported for the given
162 argument is greater than
164 .\"FreeBSD never returns EMFILE
166 .\"Too many semaphores are in use by this process.
167 .It Bq Er ENAMETOOLONG
170 argument is too long.
172 The system limit on semaphores has been reached.
175 is not set but the named semaphore does not exist.
177 There is not enough space to create the semaphore.
182 function will fail if:
187 argument is not a valid semaphore.
192 function will fail if:
195 Permission is denied to unlink the semaphore.
196 .It Bq Er ENAMETOOLONG
201 The named semaphore does not exist.
221 Support for named semaphores first appeared in