[apple/libc.git] / sys / sem_open.2

.\"	$Darwin$
.\"
.\" Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
.\"
.\" @APPLE_LICENSE_HEADER_START@
.\" 
.\" The contents of this file constitute Original Code as defined in and
.\" are subject to the Apple Public Source License Version 1.1 (the
.\" "License").  You may not use this file except in compliance with the
.\" License.  Please obtain a copy of the License at
.\" http://www.apple.com/publicsource and read it before using this file.
.\" 
.\" This Original Code and all software distributed under the License are
.\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
.\" FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
.\" License for the specific language governing rights and limitations
.\" under the License.
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.\" @APPLE_LICENSE_HEADER_END@
.\"
.Dd June 8, 2000
.Dt SEM_OPEN 2
.Os Darwin
.Sh NAME
.Nm sem_open
.Nd initialize and open a named semaphore
.Sh SYNOPSIS
.Fd #include <semaphore.h>
.Ft sem_t *
.Fn sem_open "const char *name" "int flags"
.Ft sem_t *
.Fn sem_open "const char *name" "int flags" "mode_t mode" "unsigned int value"
.Sh DESCRIPTION
The named semaphore named
.Fa name
is initialized and opened as specified by the argument
.Fa flags
and a semaphore descriptor is returned to the calling process.
.Pp
The flags specified are formed by
.Em or Ns 'ing
the following values:
.Pp
.Bd -literal -offset indent -compact
O_CREAT		create the semaphore if it does not exist
O_EXCL		error if create and semaphore exists
.Ed
.Pp
If
.Dv O_CREATE
if specified,
.Fn sem_open
requires an additional two arguments.
.Fa mode
specifies the permissions for the semaphore as described in
.Xr chmod 2
and modified by the process' umask value (see
.Xr umask 2 ) .
The semaphore is created with an initial
.Fa value ,
which must be less than or equal to
.Dv SEM_VALUE_MAX .
.Pp
If
.Dv O_EXCL
is specified and the semaphore exists,
.Fn sem_open
fails.  The check for the existence of the semaphore and the creation
of the semaphore are atomic with respect to all processes calling
.Fn sem_open
with
.Dv O_CREAT
and
.Dv O_EXCL
set.
.Pp
When a new semaphore is created, it is given the user ID and group ID
which coorespond to the effective user and group IDs of the calling
process. There is no visible entry in the file system for the created
object in this implementation.
.Pp
The returned semaphore descriptor is available to the calling process
until it is closed with
.Fn sem_close ,
or until the caller exits or execs.
.Pp
If a process makes repeated calls to
.Fn sem_open ,
with the same
.Fa name
argument, the same descriptor is returned for each successful call,
unless
.Fn sem_unlink
has been called on the semaphore in the interim.
.Pp
If
.Fn sem_open
fails for any reason, it will return a value of
.Dv SEM_FAILED
and sets
.Va errno .
On success, it returns a semaphore descriptor.
.Sh ERRORS
The named semaphore is opened unless:
.Bl -tag -width Er
.It Bq Er EACCES
The required permissions (for reading and/or writing)
are denied for the given flags; or
.Dv O_CREAT
is specified, the object does not exist, and permission to
create the semaphore is denied.
.It Bq Er EEXIST
.Dv O_CREAT
and
.Dv O_EXCL
were specified and the semaphore exists.
.It Bq Er EINTR
The
.Fn sem_open
operation was interrupted by a signal.
.It Bq Er EINVAL
The
.Fn shm_open
operation is not supported; or
.Dv O_CREAT
is specified and
.Fa value
exceeds
.Dv SEM_VALUE_MAX .
.It Bq Er EMFILE
The process has already reached its limit for semaphores or file
descriptors in use.
.It Bq Er ENAMETOOLONG
.Fa name
exceeded
.Dv SEM_NAME_LEN
characters.
.It Bq Er ENFILE
Too many semaphores or file descriptors are open on the system.
.It Bq Er ENOENT
.Dv O_CREAT
is not set and the named semaphore does not exist.
.It Bq Er ENOSPC
.Dv O_CREAT
is specified, the file does not exist, and there is insufficient
space available to create the semaphore.
.El
.Sh SEE ALSO
.Xr semctl 2 ,
.Xr semget 2 ,
.Xr semop 2 ,
.Xr sem_close 2 ,
.Xr sem_post 2 ,
.Xr sem_trywait 2 ,
.Xr sem_unlink 2 ,
.Xr sem_wait 2 ,
.Xr umask 2
.Sh HISTORY
.Fn sem_open
is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995).
Commit	Line	Data
e9ce8d39 A	1	.\" $Darwin$
e9ce8d39 A	2	.\"
5b2abdfb	3	.\" Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
e9ce8d39 A	4	.\"
	5	.\" @APPLE_LICENSE_HEADER_START@
	6	.\"
	7	.\" The contents of this file constitute Original Code as defined in and
	8	.\" are subject to the Apple Public Source License Version 1.1 (the
	9	.\" "License"). You may not use this file except in compliance with the
	10	.\" License. Please obtain a copy of the License at
	11	.\" http://www.apple.com/publicsource and read it before using this file.
	12	.\"
	13	.\" This Original Code and all software distributed under the License are
	14	.\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
	15	.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
	16	.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
	17	.\" FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
	18	.\" License for the specific language governing rights and limitations
	19	.\" under the License.
	20	.\"
	21	.\" @APPLE_LICENSE_HEADER_END@
	22	.\"
	23	.Dd June 8, 2000
	24	.Dt SEM_OPEN 2
	25	.Os Darwin
	26	.Sh NAME
	27	.Nm sem_open
	28	.Nd initialize and open a named semaphore
	29	.Sh SYNOPSIS
	30	.Fd #include <semaphore.h>
	31	.Ft sem_t *
	32	.Fn sem_open "const char *name" "int flags"
	33	.Ft sem_t *
	34	.Fn sem_open "const char *name" "int flags" "mode_t mode" "unsigned int value"
	35	.Sh DESCRIPTION
	36	The named semaphore named
	37	.Fa name
	38	is initialized and opened as specified by the argument
	39	.Fa flags
	40	and a semaphore descriptor is returned to the calling process.
	41	.Pp
	42	The flags specified are formed by
	43	.Em or Ns 'ing
	44	the following values:
	45	.Pp
	46	.Bd -literal -offset indent -compact
	47	O_CREAT create the semaphore if it does not exist
	48	O_EXCL error if create and semaphore exists
	49	.Ed
	50	.Pp
	51	If
	52	.Dv O_CREATE
	53	if specified,
	54	.Fn sem_open
	55	requires an additional two arguments.
	56	.Fa mode
	57	specifies the permissions for the semaphore as described in
	58	.Xr chmod 2
	59	and modified by the process' umask value (see
	60	.Xr umask 2 ) .
	61	The semaphore is created with an initial
	62	.Fa value ,
	63	which must be less than or equal to
	64	.Dv SEM_VALUE_MAX .
	65	.Pp
	66	If
	67	.Dv O_EXCL
68	is specified and the semaphore exists,
69	.Fn sem_open
70	fails. The check for the existence of the semaphore and the creation
71	of the semaphore are atomic with respect to all processes calling
72	.Fn sem_open
73	with
74	.Dv O_CREAT
75	and
76	.Dv O_EXCL
77	set.
78	.Pp
79	When a new semaphore is created, it is given the user ID and group ID
80	which coorespond to the effective user and group IDs of the calling
81	process. There is no visible entry in the file system for the created
82	object in this implementation.
83	.Pp
84	The returned semaphore descriptor is available to the calling process
85	until it is closed with
86	.Fn sem_close ,
87	or until the caller exits or execs.
88	.Pp
89	If a process makes repeated calls to
90	.Fn sem_open ,
91	with the same
92	.Fa name
93	argument, the same descriptor is returned for each successful call,
94	unless
95	.Fn sem_unlink
96	has been called on the semaphore in the interim.
97	.Pp
98	If
99	.Fn sem_open
100	fails for any reason, it will return a value of
101	.Dv SEM_FAILED
102	and sets
103	.Va errno .
104	On success, it returns a semaphore descriptor.
105	.Sh ERRORS
106	The named semaphore is opened unless:
107	.Bl -tag -width Er
108	.It Bq Er EACCES
109	The required permissions (for reading and/or writing)
110	are denied for the given flags; or
111	.Dv O_CREAT
112	is specified, the object does not exist, and permission to
113	create the semaphore is denied.
114	.It Bq Er EEXIST
115	.Dv O_CREAT
116	and
117	.Dv O_EXCL
118	were specified and the semaphore exists.
119	.It Bq Er EINTR
120	The
121	.Fn sem_open
122	operation was interrupted by a signal.
123	.It Bq Er EINVAL
124	The
125	.Fn shm_open
126	operation is not supported; or
127	.Dv O_CREAT
128	is specified and
129	.Fa value
130	exceeds
131	.Dv SEM_VALUE_MAX .
132	.It Bq Er EMFILE
133	The process has already reached its limit for semaphores or file
134	descriptors in use.
135	.It Bq Er ENAMETOOLONG
136	.Fa name
137	exceeded
138	.Dv SEM_NAME_LEN
139	characters.
140	.It Bq Er ENFILE
141	Too many semaphores or file descriptors are open on the system.
142	.It Bq Er ENOENT
143	.Dv O_CREAT
144	is not set and the named semaphore does not exist.
145	.It Bq Er ENOSPC
146	.Dv O_CREAT
147	is specified, the file does not exist, and there is insufficient
148	space available to create the semaphore.
149	.El
150	.Sh SEE ALSO
151	.Xr semctl 2 ,
152	.Xr semget 2 ,
153	.Xr semop 2 ,
154	.Xr sem_close 2 ,
155	.Xr sem_post 2 ,
156	.Xr sem_trywait 2 ,
157	.Xr sem_unlink 2 ,
158	.Xr sem_wait 2 ,
159	.Xr umask 2
160	.Sh HISTORY
161	.Fn sem_open
162	is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995).