semop.2 (2010 09)

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semop(2) semop(2)

NAME

semop(), semtimedop() - semaphore operations

SYNOPSIS

#include <sys/sem.h>

#include <sys/time.h>

int semop(

int semid,

struct sembuf *sops,

size_t nsops

);

int semtimedop(

int semid,

struct sembuf *sops,

size_t nsops,

const struct timespec *timeout

);

DESCRIPTION

semop() is used to atomically perform an array of semaphore operations on the set of semaphores asso-

ciated 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:

ushort 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. Semaphore array operations are atomic in that none of the semaphore operations

are performed until blocking conditions on all of the semaphores in the array have been removed.

sem_op speciﬁes one of three semaphore operations as follows:

• If sem_op is a negative integer, one of the following occurs:

If semaphore value (see semaphore identiﬁer in glossary (9)) is greater than or equal to the abso-

lute value of sem_op, the absolute value of sem_op is subtracted from semaphore value. Also, if

(sem_ﬂg &

SEM_UNDO) is "true", the absolute value of sem_op is added to the calling process’s

semadj value (see glossary (9) and exit (2)) for the speciﬁed semaphore.

If semaphore value is less than the absolute value of sem_op and (sem_ﬂg &

IPC_NOWAIT)is

"true",

semop() returns immediately.

If semaphore value is less than the absolute value of sem_op and (sem_ﬂg &

IPC_NOWAIT)is

‘‘false’’,

semop() increments the internal semaphore waiter count associated with the speciﬁed

semaphore and suspend execution of the calling process until one of the following conditions

occur:

Semaphore value becomes greater than or equal to the absolute value of sem_op . When

this occurs, the value of internal semaphore waiter count associated with the speciﬁed

semaphore is decremented, the absolute value of sem_op is subtracted from semaphore

value 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 −1is

returned.

The calling process receives a signal that is to be caught. When this occurs, the value of

internal semaphore waiter count associated with the speciﬁed semaphore is decremented,

and the calling process resumes execution in the manner prescribed in signal (5).

• If sem_op is a positive integer, the value of sem_op is added to semaphore value 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.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
semop(2) semop(2) NAME semop(), semtimedop() - semaphore operations SYNOPSIS #include #include int semop( int semid, struct sembuf *sops, size_t nsops ); int semtimedop( int semid, struct sembuf *sops, size_t nsops, const struct timespec *timeout ); DESCRIPTION semop() is used to atomically perform 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 semaphoreoperation structures.
PAGE 2
semop(2) • semop(2) If sem_op is zero, one of the following occurs: If semaphore value is zero, semop() proceeds to the next semaphore operation specified by sops , or returns immediately if this is the last operation. If semaphore value is not equal to zero and (sem_flg & IPC_NOWAIT) is "true", semop() returns immediately.
PAGE 3
semop(2) [EAGAIN] semop(2) The operation would result in suspension of the calling process but (sem_flg & IPC_NOWAIT) is "true". [ENOSPC] [EINVAL] The limit on the number of individual processes requesting an SEM_UNDO would be exceeded. The number of individual semaphores for which the calling process requests a SEM_UNDO would exceed the limit. [ERANGE] An operation would cause a semaphore value to overflow the system-imposed limit.
PAGE 4
(Notes) A (Notes) sA 4 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010