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

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