semop.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 307 行

.\" SCCSID: @(#)semop.2	8.1	9/11/90
.TH semop 2
.SH Name
semop \- semaphore operations
.SH Syntax
.nf
.B #include <sys/types.h>
.B #include <sys/ipc.h>
.B #include <sys/sem.h>
.PP
.B int semop (\fIsemid, sops, nsops\fP)
.B int \fIsemid\fP;
.B struct sembuf *\fIsops[]\fP;
.B int \fInsops\fP;
.fi
.SH Description
.NXB "semop system call"
.NXB "semaphore" "operations"
.NXA "semop system call" "semctl system call"
.NXA "semop system call" "semget system call"
The
.PN semop
system call
is used to atomically perform an
array of semaphore operations on the set of
semaphores associated with the semaphore identifier specified by 
.PN semid .
The
.I sops
is a pointer to the array of semaphore-operation structures.
The
.I nsops
is the number of such structures in the array.
The contents of each structure
includes the following members:
.EX
short	sem_num;	/* semaphore number */
short	sem_op;	/* semaphore operation */
short	sem_flg;	/* operation flags */
.EE
.PP
Each semaphore operation specified by
.I sem_op
is performed on the corresponding semaphore specified by
.PN semid
and
.IR sem_num .
.PP
The
.I sem_op
specifies one of three semaphore operations as follows:
.PP
.B 1.
If
.I sem_op
is a negative integer, one of the following occurs: 
.IP \(bu 4
If 
.I semval
is greater than or equal to the absolute value of
.I sem_op,
the absolute value of
.I sem_op
is subtracted from 
.I semval.  
For further information, see 
.MS intro 2 .
Also, if 
.RI ( sem_flg
& SEM_UNDO)
is true, the absolute value of
.I sem_op
is added to the calling process's 
.I semadj 
value for the specified semaphore.
For further information, see 
.MS exit 2 .
.IP \(bu
If 
.I semval
is less than the absolute value of
.I sem_op
and 
.RI ( sem_flg
& IPC_NOWAIT)
is true, 
.PN semop
returns immediately.
.IP \(bu
If 
.I semval
is less than the absolute value of
.I sem_op
and 
.IR ( sem_flg
& IPC_NOWAIT )
is false, 
.PN semop
increments the 
.I semncnt 
associated with the specified semaphore and
suspend execution of the calling
process until one of the following occurs:
.IP \(bu
If the
.I semval
becomes greater than
or equal to the absolute value of 
.I sem_op.
When this occurs, the value of
semncnt associated with the specified
semaphore is decremented, the absolute value of 
.I sem_op
is subtracted from 
.I semval,
and if 
.RI ( sem_flg
& SEM_UNDO)
is true, the absolute value of
.I sem_op
is added to the calling process's
.I semadj 
value for the specified semaphore.
.IP
The 
.PN semid
for which the calling
process is awaiting action is removed
from the system.  For further information, see
.MS semctl 2 .
When this occurs, 
.I errno
is set equal to EIDRM, and a value of \-1 is returned.
.PP
The calling process receives a signal
that is to be caught.  When this occurs,
the value of 
.I semncnt 
associated with the specified semaphore is decremented,
and the calling process resumes execution
in the manner prescribed in 
.MS signal 3 .
.PP
.B 2.
If
.I sem_op
is a positive integer, the value of 
.I sem_op
is added to 
.I semval
and, if 
.RI ( sem_flg
& SEM_UNDO)
is true, the value of 
.I sem_op
is subtracted from the calling process's 
.I semadj 
value for the specified semaphore. 
.PP
.B 3.
If
.I sem_op 
is zero, one of the following occurs:
.IP \(bu 4
If 
.I semval
is zero,
.PN semop
returns immediately.
.IP \(bu
If 
.I semval
is not equal to zero and 
.RI ( sem_flg
& IPC_NOWAIT)
is true,
.PN semop
returns immediately.
.IP \(bu
If 
.I semval
is not equal to zero and 
.RI ( sem_flg
& IPC_NOWAIT)
is false, 
.PN semop
increments the 
.I semzcnt 
associated with the specified semaphore and suspend
execution of the calling process, until
one of the following occurs:
.IP
The
.I semval
became zero, at which time
the value of 
.I semzcnt 
associated with the specified semaphore is decremented.
.IP
The 
.PN semid
for which the calling process
is awaiting action is removed from the
system.  When this occurs,
.I errno
is set equal to EIDRM, and a value of \-1 is returned.
.PP
The calling process receives a signal
that is to be caught.  When this occurs,
the value of 
.I semzcnt
associated with
the specified semaphore is decremented,
and the calling process resumes execution
in the manner prescribed in 
.MS signal 3 .
.RE
.PP
Upon successful completion, the value of 
.I sempid 
for each semaphore
specified in the array pointed to by
.I sops
is set equal to the process ID of the calling process.
.SH Return Values
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned, and 
.I errno
is set to indicate the error.
.SH Diagnostics
.NXR "semop system call" "diagnostics"
The
.PN semop
fails if any of the following is true for any of the
semaphore operations specified by 
.IR sops:
.TP 15
[EINVAL]
The
.I sempid
is not a valid semaphore identifier. 
.TP 15
[EFBIG]
The
.I sem_num
is less than zero or greater than or
equal to the number of semaphores
in the set associated with
.PN semid .
.TP 15
[E2BIG]
The
.I nsops
is greater than the system-imposed maximum. 
.TP 15
[EACCESS]
Operation permission is denied to the calling process.
For further information, see 
.MS errno 2 . 
.TP 15
[EAGAIN]
The operation would result in suspension of the calling process, but 
.RI ( sem_flg
&
IPC_NOWAIT)
is true. 
.TP 15
[ENOSPC]
The limit on the number of individual processes requesting an 
SEM_UNDO
would be exceeded. 
.TP 15
[EINVAL]
The number of individual semaphores
for which the calling process request a
SEM_UNDO
would exceed the limit. 
.TP 15
[ERANGE]
An operation would cause a 
.I semval
to overflow the system-imposed limit.
.TP 15
[ERANGE]
An operation would cause a 
.I semadj 
value to overflow the system-imposed limit. 
.TP 15
[EFAULT]
The
.I sops
points to an illegal address. 
.TP 15
[EINTR]
The
.PN semop
returns due to the receipt of a signal.
.TP
[EIDRM]
The
.PN semid
has been removed from the system.
.SH See Also
execve(2), exit(2), fork(2), semctl(2), semget(2), signal(3)
.NXE "semop system call"
.NXE "semaphore" "operations"