semop(2) System Calls semop(2)NAME
semop, semtimedop - semaphore operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.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
The semop() function is used to perform atomically an array of sema‐
phore operations on the set of semaphores associated with the semaphore
identifier specified by semid. The sops argument is a pointer to the
array of semaphore-operation structures. The nsops argument is the num‐
ber of such structures in the array.
Each sembuf structure contains 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 corre‐
sponding semaphore specified by semid and sem_num. The permission
required for a semaphore operation is given as {token}, where token is
the type of permission needed. The types of permission are interpreted
as follows:
00400 READ by user
00200 ALTER by user
00040 READ by group
00020 ALTER by group
00004 READ by others
00002 ALTER by others
See the Semaphore Operation Permissions section of intro(2) for more
information.
A process maintains a value, semadj, for each semaphore it modifies.
This value contains the cumulative effect of operations the process has
performed on an individual semaphore with the SEM_UNDO flag set (so
that they can be undone if the process terminates unexpectedly). The
value of semadj can affect the behavior of calls to semop(), semtime‐
dop(), exit(), and _exit() (the latter two functions documented on
exit(2)), but is otherwise unobservable. See below for details.
The sem_op member specifies one of three semaphore operations:
1. The sem_op member is a negative integer; {ALTER}
· If semval (see intro(2)) is greater than or equal to the abso‐
lute value of sem_op, the absolute value of sem_op is sub‐
tracted 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(2)) for the specified semaphore.
· If semval is less than the absolute value of sem_op and
(sem_flg&IPC_NOWAIT) is true, semop() returns immediately.
· If semval is less than the absolute value of sem_op and
(sem_flg&IPC_NOWAIT) is false, semop() increments the semncnt
associated with the specified semaphore and suspends execution
of the calling thread until one of the following conditions
occur:
· The value of 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 decre‐
mented, 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 thread is awaiting action
is removed from the system (see semctl(2)). When this
occurs, errno is set to EIDRM and −1 is returned.
· The calling thread 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 thread resumes execution in the manner prescribed
in sigaction(2).
2. The sem_op member is a positive integer; {ALTER}
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.
3. The sem_op member is 0; {READ}
· If semval is 0, semop() returns immediately.
· If semval is not equal to 0 and (sem_flg&IPC_NOWAIT) is true,
semop() returns immediately.
· If semval is not equal to 0 and (sem_flg&IPC_NOWAIT) is false,
semop() increments the semzcnt associated with the specified
semaphore and suspends execution of the calling thread until
one of the following occurs:
· The value of semval becomes 0, at which time the value of
semzcnt associated with the specified semaphore is set to
0 and all processes waiting on semval to become 0 are
awakened.
· The semid for which the calling thread is awaiting action
is removed from the system. When this occurs, errno is
set to EIDRM and −1 is returned.
· The calling thread 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 thread resumes execution in the manner prescribed
in sigaction(2).
Upon successful completion, the value of sempid for each semaphore
specified in the array pointed to by sops is set to the process ID of
the calling process.
The semtimedop() function behaves as semop() except when it must sus‐
pend execution of the calling process to complete its operation. If
semtimedop() must suspend the calling process after the time interval
specified in timeout expires, or if the timeout expires while the
process is suspended, semtimedop() returns with an error. If the time‐
spec structure pointed to by timeout is zero-valued and semtimedop()
needs to suspend the calling process to complete the requested opera‐
tion(s), it returns immediately with an error. If timeout is the NULL
pointer, the behavior of semtimedop() is identical to that of semop().
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned
and errno is set to indicate the error.
ERRORS
The semop() and semtimedop() functions will fail if:
E2BIG The nsops argument is greater than the system-imposed
maximum. See NOTES.
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 The sops argument points to an illegal address.
EFBIG The value of sem_num is less than 0 or greater than or
equal to the number of semaphores in the set associated
with semid.
EIDRM A semid was removed from the system.
EINTR A signal was received.
EINVAL The semid argument is not a valid semaphore identifier,
or the number of individual semaphores for which the
calling process requests a SEM_UNDO operation would
exceed the system-imposed limit. Solaris does not
impose a limit on the number of individual semaphores
for which the calling process requests a SEM_UNDO oper‐
ation.
ENOSPC The limit on the number of individual processes
requesting a SEM_UNDO operation would be exceeded.
Solaris does not impose a limit on the number of indi‐
vidual processes requesting an SEM_UNDO operation.
ERANGE An operation would cause a semval or a semadj value to
overflow the system-imposed limit.
The semtimedop() function will fail if:
EAGAIN The timeout expired before the requested operation
could be completed.
The semtimedop() function will fail if one of the following is
detected:
EFAULT The timeout argument points to an illegal address.
EINVAL The timeout argument specified a tv_sec or tv_nsec
value less than 0, or a tv_nsec value greater than or
equal to 1000 million.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │semop() is Standard. │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOipcs(1), rctladm(1M), intro(2), exec(2), exit(2), fork(2), semctl(2),
semget(2), setrctl(2), sigaction(2), attributes(5), standards(5)NOTES
The system-imposed maximum on nsops for a semaphore identifier is the
minimum enforced value of the process.max-sem-ops resource control of
the creating process at the time semget(2) was used to allocate the
identifier.
See rctladm(1M) and setrctl(2) for information about using resource
controls.
SunOS 5.10 12 May 2006 semop(2)
