semop, semtimedop - semaphore operations
#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);
The semop() function is used to perform atomically an array
of semaphore 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 number 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 corresponding 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(), semtimedop(), 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}
- o
- 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(2)) for the specified semaphore.
- o
- If semval is less than the absolute value of sem_op and
(sem_flg&IPC_NOWAIT) is true, semop() returns
immediately.
- o
- 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:
- o
- 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 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.
- o
- 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.
- o
- 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}
- o
- If semval is 0, semop() returns immediately.
- o
- If semval is not equal to 0 and
(sem_flg&IPC_NOWAIT) is true, semop() returns
immediately.
- o
- 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:
- o
- 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.
- o
- 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.
- o
- 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 suspend 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 timespec structure pointed to by timeout is zero-valued
and semtimedop() needs to suspend the calling process to complete the
requested operation(s), it returns immediately with an error. If
timeout is the NULL pointer, the behavior of
semtimedop() is identical to that of semop().
Upon successful completion, 0 is returned. Otherwise,
−1 is returned and errno is set to indicate the
error.
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 operation.
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 individual 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.
See attributes(7) for descriptions of the following
attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
semop() is Standard. |
ipcs(1), Intro(2), exec(2), exit(2),
fork(2), semctl(2), semget(2), setrctl(2),
sigaction(2), attributes(7), standards(7),
rctladm(8)
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(8) and setrctl(2) for information about
using resource controls.