HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man2/!!!intro.2
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s
semop(2) semop(2)
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(5).
EXAMPLES
The following call to semop() atomically performs a "P" or "get" operation on the second semaphore in
the semaphore set and a "V" or "release" operation on the third semaphore in the set. This example
assumes the process has a valid semid which represents a set of 4 semaphores as shown on the semget(2)
manual page. It also assumes that the semvals of the semaphores in the set have been initialized as shown
in the semctl(2) manual entry.
struct sembuf sops[4];
sops[0].sem_num = 1;
sops[0].sem_op = -1; /* P (get) */
sops[0].sem_flg = 0;
sops[1].sem_num = 2;
sops[1].sem_op = 1; /* V (release) */
sops[1].sem_flg = 0;
semop (mysemid, sops, 2);
RETURN VALUE
If semop() returns due to the receipt of a signal, a value of −1 is returned to the calling process and
errno is set to EINTR. If it returns due to the removal of a semid from the system, a value of −1is
returned and
errno is set to EIDRM.
Upon successful completion, a non-negative value is returned. Otherwise, a value of −1 is returned and
errno is set to indicate the error.
ERRORS
semop() fails if one or more of the following is true for any of the semaphore operations specified by sops:
[EINVAL] semid is not a valid semaphore identifier.
[EFBIG] sem_num is less than zero or greater than or equal to the number of semaphores in
the set associated with semid.
[E2BIG] nsops is greater than the system-imposed maximum.
[EACCES] Operation permission is denied to the calling process (see glossary(9)).
[EAGAIN] The operation would result in suspension of the calling process but (sem_flg &
IPC_NOWAIT) is ‘‘true’’.
[ENOSPC] The limit on the number of individual processes requesting an SEM_UNDO would be
exceeded.
[EINVAL] The number of individual semaphores for which the calling process requests a
SEM_UNDO would exceed the limit.
[ERANGE] An operation would cause a semval to overflow the system-imposed limit.
[ERANGE] An operation would cause a semadj value to overflow the system-imposed limit.
[EFAULT] sops points to an illegal address. The reliable detection of this error will be implemen-
tation dependent.
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. The value of sem_otime in the data structure
associated with the semaphore identifier will be set to the current time.
Section 2−−292 − 2 − HP-UX Release 11i: December 2000
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