waitsem(2xnx) (XENIX System Compatibility)


waitsem, nbwaitsem -- (XENIX) await and check access to a resource governed by a semaphore

Synopsis

   cc [flag . . . ] flag . . . -lx 
   

int waitsem(int sem_num);

int nbwaitsem(int sem_num);

Description

waitsem gives the calling process access to the resource governed by the semaphore sem_num. If the resource is in use by another process, waitsem will put the process to sleep until the resource becomes available; nbwaitsem will return the error ENAVAIL. waitsem and nbwaitsem are used in conjunction with sigsem to allow synchronization of processes waiting to access a resource. One or more processes may waitsem on the given semaphore and will be put to sleep until the process which currently has access to the resource issues sigsem. sigsem causes the process which is next in line on the semaphore's queue to be rescheduled for execution. The semaphore's queue is organized in First In, First Out (FIFO) order.

Return values

waitsem returns the value (int) -1 if an error occurs. If sem_num has not been previously opened by a call to opensem or creatsem, errno is set to EBADF. If sem_num does not refer to a semaphore type file, errno is set to ENOTNAM. All processes waiting (or attempting to wait) on the semaphore return with errno set to ENAVAIL when the process controlling the semaphore exits without relinquishing control (thereby leaving the resource in an undeterminate state). If a process does two waitsems in a row without doing a intervening sigsem, errno is set to EINVAL.

References

creatsem(2xnx), opensem(2xnx)
30 January 1998
© 1998 The Santa Cruz Operation, Inc. All rights reserved.