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Manual Pages for UNIX Operating System command usage for man semtimedop

System Calls semop(2)

NAME

semop, semtimedop - semaphore operations

SYNOPSIS

#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

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 struc-

tures 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.

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System Calls semop(2) 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 sema-

phore 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(), sem-

timedop(), 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 opera-

tions:

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 follow-

ing 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 associ-

ated 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. 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

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System Calls semop(2) is to be caught. When this occurs, the

value of semncnt associated with the speci-

fied semaphore is decremented, and the cal-

ling 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() incre-

ments 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 speci-

fied semaphore is decremented, and the cal-

ling 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.

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System Calls semop(2)

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 com-

plete 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. See NOTES.

EACCES Operation permission is denied to the calling pro-

cess (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 iden-

tifier, 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 pro-

cess requests a SEM_UNDO operation.

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System Calls semop(2) 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 opera-

tion. 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 attri-

butes:

____________________________________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

|_____________________________|_____________________________|

| Interface Stability | semop() is Standard. |