sem_trywait(2) [hpux man page]

sem_wait(2)							System Calls Manual						       sem_wait(2)

NAME

       sem_wait, sem_trywait - lock a POSIX semaphore

SYNOPSIS

DESCRIPTION

       is  used to lock a semaphore.  The calling thread will not return from its call to until one of the following events occur: it successfully
       obtains a lock on the semaphore; it is interrupted by a signal or an error condition occurs.

       is used to lock a semaphore, if it is available.  The value of the semaphore sem is checked at some unspecified time during the	call.	If
       the semaphore is available at the time its value is checked, the calling thread will atomically, with respect to the checking of the value,
       lock the semaphore.  The thread will now own a lock on the semaphore; the call will return successfully.  If the semaphore  is  unavailable
       at the time its value is checked, then the call returns -1 with errno set to EAGAIN.

       If  the	specified semaphore referred to by sem is a named semaphore, then this semaphore must have been opened by the calling process with
       The calling process must have both read and write permissions on the semaphore to perform these operations.  The semaphore will	be  locked
       upon successful return and will stay locked until it is explicitly released by a call to

       To use this function, link in the realtime library by specifying on the compiler or linker command line.

EXAMPLES

       The following call to will lock the semaphore sem.

       The following call to will lock the semaphore sem, if it is available.

RETURN VALUE

       A  successful  call  to	will return 0 and the calling thread will then own a lock on the semaphore.  Otherwise, the call to will return -1
       with errno set to the appropriate value of the error condition.

       A successful call to will return 0, if the semaphore was available and the calling thread was able to lock the semaphore.   Otherwise,  the
       call to will return -1 with errno set to the appropriate value of the error condition.

ERRORS

       and fail and do not perform the requested operation if any of the following conditions are encountered:

	      [EPERM]	     The calling process does not have the privileges necessary to lock the semaphore.

	      [EAGAIN]	     The semaphore was not available and hence could not be locked by This error condition only occurs in

	      [EINVAL]	     The argument sem does not refer to a valid semaphore.

	      [EINTR]	     The function was interrupted by a signal

SEE ALSO

       sem_post(2), <semaphore.h>.

STANDARDS CONFORMANCE

																       sem_wait(2)

Check Out this Related Man Page

SEM_TIMEDWAIT(3)					   BSD Library Functions Manual 					  SEM_TIMEDWAIT(3)

NAME

     sem_timedwait -- lock a semaphore

LIBRARY

     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

     #include <semaphore.h>

     int
     sem_timedwait(sem_t *sem, const struct timespec *abs_timeout);

DESCRIPTION

     The sem_timedwait() function locks the semaphore referenced by sem, as in the sem_wait(3) function.  However, if the semaphore cannot be
     locked without waiting for another process or thread to unlock the semaphore by performing a sem_post(3) function, this wait will be termi-
     nated when the specified timeout expires.

     The timeout will expire when the absolute time specified by abs_timeout passes, as measured by the clock on which timeouts are based (that
     is, when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at
     the time of the call.

     Note that the timeout is based on the CLOCK_REALTIME clock.

     The validity of the abs_timeout is not checked if the semaphore can be locked immediately.

RETURN VALUES

     The sem_timedwait() function returns zero if the calling process successfully performed the semaphore lock operation on the semaphore desig-
     nated by sem.  If the call was unsuccessful, the state of the semaphore is unchanged, and the function returns a value of -1 and sets the
     global variable errno to indicate the error.

ERRORS

     The sem_timedwait() function will fail if:

     [EINVAL]		The sem argument does not refer to a valid semaphore, or the process or thread would have blocked, and the abs_timeout
			parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.

     [ETIMEDOUT]	The semaphore could not be locked before the specified timeout expired.

     [EINTR]		A signal interrupted this function.

SEE ALSO

     sem_post(3), sem_trywait(3), sem_wait(3)

STANDARDS

     The sem_timedwait() function conforms to IEEE Std 1003.1-2004 (``POSIX.1'').

HISTORY

     The function first appeared in FreeBSD 5.0.

BSD
								   March 3, 2008							       BSD

Linux and UNIX Man Pages

sem_trywait(2) [hpux man page]

Check Out this Related Man Page