semtimedop(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SUMMARY OF TRUSTED SOLARIS CHANGES | SEE ALSO

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 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.

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 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.

   • 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 process 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 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 to EIDRM and -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(3C).

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 process 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 decremented.

     • The semid for which the calling process is awaiting action is removed from the system. When this occurs, errno is set to EIDRM and -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(3C).

If sem_op() is zero {READ}, the process must have discretionary and mandatory read access to the semaphore structure to which semid refers. Overriding these checks requires that the effective privilege set of the process include one or both of these privileges as necessary: PRIV_IPC_DAC_READ and PRIV_IPC_MAC_READ.

If sem_op() is a positive or a negative number {ALTER}, the process must have discretionary and mandatory write access to the semaphore structure to which semid refers. Overriding these checks requires that the effective privilege set of the process include one or both of these privileges as necessary: PRIV_IPC_DAC_WRITE and PRIV_IPC_MAC_WRITE.

Upon successful completion, the value of semid 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().

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.

EACCES

Operation permission is denied to the calling process (see intro(2)), and the calling process does not have the appropriate privilege(s) in its set of effective privileges.

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 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 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.

SUMMARY OF TRUSTED SOLARIS CHANGES

Appropriate privilege is required to override access checks.

SEE ALSO

Trusted Solaris 8 4/01 Reference Manual

ipcs(1), Intro(2), exec(2), fork(2), semctl(2), semget(2)

SunOS 5.8 Reference Manual

signal(3C)

Trusted Solaris 8 4/01  Last Revised 15 Oct 2000

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SUMMARY OF TRUSTED SOLARIS CHANGES | SEE ALSO