Manual page for SEMOP(2)
semop - semaphore operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semop(semid, sops, nsops)
int semid;
struct sembuf *sops;
int nsops;
DESCRIPTION
semop()
is used to perform atomically an array of semaphore operations on the
set of semaphores associated with the semaphore identifier specified by
semid.
sops
is a pointer to the array of semaphore-operation structures.
nsops
is the number of such structures in the array.
The contents of each structure includes the following members:
-
short sem_num; /* semaphore number */
short sem_op; /* semaphore operation */
short sem_flg; /* operation flags */
Each semaphore operation specified by
sem_op
is performed on the corresponding semaphore specified by
semid
and
sem_num.
sem_op
specifies one of three semaphore operations as follows:
-
If
sem_op
is a negative integer, one of the following will occur:
[ALTER]
(see
semctl.2
- If
semval
(see
intro.2
is greater than or equal to the absolute value of
sem_op(),
the absolute value of
sem_op()
is subtracted from
semval.
Also, if
(sem_flg &
SEM_UNDO)
is ``true'', the absolute value of
sem_op()
is added to the calling process's
semadj
value (see
exit.2v
for the specified semaphore.
- If
semval
is less than the absolute value of
sem_op()
and
(sem_flg &
IPC_NOWAIT)
is ``true'',
semop()
will return immediately.
- If
semval
is less than the absolute value of
sem_op()
and
(sem_flg &
IPC_NOWAIT)
is ``false'',
semop()
will increment the
semncnt
associated with the specified semaphore
and suspend execution of the calling process
until one of the following conditions occur.
-
semval
becomes greater than or equal to the absolute value of
sem_op().
When this occurs, the value of
semncnt
associated with the specified
semaphore is decremented, the absolute value of
sem_op()
is subtracted from
semval
and, if
(sem_flg &
SEM_UNDO)
is ``true'', the absolute value of
sem_op()
is added to the calling process's
semadj
value for the specified semaphore.
The
semid
for which the calling process is awaiting action
is removed from the system (see
semctl.2
When this occurs,
errno
is set equal to
EIDRM,
and a value of -1 is returned.
The calling process receives a signal that is to be caught.
When this occurs, the value of
semncnt
associated with the specified
semaphore is decremented,
and the calling process resumes execution in the manner prescribed in
signal.3v
If
sem_op()
is a positive integer, the value of
sem_op()
is added to
semval
and, if
(sem_flg &
SEM_UNDO)
is ``true'', the value of
sem_op()
is subtracted from the calling process's
semadj
value for the specified
semaphore.
[ALTER]
If
sem_op()
is zero,
one of the following will occur:
[READ]
- If
semval
is zero,
semop()
will return immediately.
- If
semval
is not equal to zero and
(sem_flg &
IPC_NOWAIT)
is ``true'',
semop()
will return immediately.
- If
semval
is not equal to zero and
(sem_flg &
IPC_NOWAIT)
is ``false'',
semop()
will increment the
semzcnt
associated with the specified semaphore
and suspend execution of the calling process until
one of the following occurs:
-
- semval
becomes zero, at which time the value of
semzcnt
associated with the
specified semaphore is decremented.
- The
semid
for which the calling process is awaiting action
is removed from the system.
When this occurs,
errno
is set equal to
EIDRM,
and a value of -1 is returned.
- The calling process receives a signal that is to be caught.
When this occurs, the value of
semzcnt
associated with the specified semaphore is decremented,
and the calling process resumes execution in the manner prescribed in
signal.3v
Upon successful completion, the value of
sempid
for each semaphore specified in the array pointed to by
sops
is set equal to the process
ID
of the calling process.
RETURN VALUES
semop()
returns:
- 0
-
on success.
- -1
-
on failure and sets
errno
to indicate the error.
ERRORS
- E2BIG
-
nsops
is greater than the system-imposed maximum.
- EACCES
-
Operation permission is denied to the calling process (see
intro.2
- EAGAIN
-
The operation would result in suspension of the calling process but
(sem_flg &
IPC_NOWAIT)
is ``true''.
- EFAULT
-
sops
points to an illegal address.
- EFBIG
-
sem_num
is less than zero or greater than or equal to the number of semaphores
in the set associated with
semid.
- EIDRM
-
The set of semaphores referred to by
msqid
was removed from the system.
- EINTR
-
The call was interrupted by the delivery of a signal.
- EINVAL
-
semid
is not a valid semaphore identifier.
The number of individual semaphores for which the calling process
requests a
SEM_UNDO
would exceed the limit.
- ENOSPC
-
The limit on the number of individual processes requesting an
SEM_UNDO
would be exceeded.
- ERANGE
-
An operation would cause a
semval
or
semadj
value to overflow the system-imposed limit.
SEE ALSO
ipcrm.1
ipcs.1
intro.2
execve.2v
exit.2v
fork.2v
semctl.2
semget.2
signal.3v
Created by unroff & hp-tools.
© somebody (See intro for details). All Rights Reserved.
Last modified 11/5/97