_lwp_park(2) [netbsd man page]

_LWP_PARK(2)						      BSD System Calls Manual						      _LWP_PARK(2)

NAME

     _lwp_park -- wait interruptably in the kernel

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <lwp.h>

     int
     _lwp_park(const struct timespec *abstime, lwpid_t unpark, const void *hint, const void *unparkhint);

DESCRIPTION

     _lwp_park() can be used to synchronize access to resources among multiple light-weight processes.	It causes the calling LWP to wait inter-
     ruptably in the kernel, until one of the following conditions is met:

     o	 The abstime argument is non-NULL, and the absolute UTC time it specifies has passed.

     o	 The LWP receives a directed signal posted using _lwp_kill(), or is elected to handle a signal on behalf of its containing process.

     o	 The LWP is awoken by another LWP in the same process that has made a call to _lwp_wakeup().

     o	 The LWP is awoken by another LWP in the same process that has made a call to _lwp_unpark() or _lwp_unpark_all().

     The preferred method to awaken an LWP sleeping as a result of a call to _lwp_park() is to make a call to _lwp_unpark(), or _lwp_unpark_all().
     The _lwp_wakeup() system call is a more general facility, and requires more resources to execute.

     The optional hint argument specifies the address of object upon which the LWP is synchronizing.  When the hint value is matched between calls
     to _lwp_park() and _lwp_unpark() or _lwp_unpark_all(), it may reduce the time necessary for the system to resume execution of waiting LWPs.

     The unpark and unparkhint arguments can be used to fold a park operation and unpark operation into a single system call.  If unpark is non-
     zero, the system will behave as if the following call had been made before the calling thread begins to wait:

	     _lwp_unpark(unpark, unparkhint);

RETURN VALUES

     _lwp_park() may return a value of 0.  Otherwise, -1 is returned and errno is set to provide more information.

ERRORS

     [EALREADY]
	       A request was made to wake the LWP before it began to wait in the kernel.

     [EINTR]   The LWP has been awoken by a signal or by a call to one of the following functions: _lwp_unpark(), _lwp_unpark_all(),
	       _lwp_wakeup().

     [EINVAL]  The time value specified by abstime is invalid.

     [ESRCH]   No LWP can be found in the current process corresponding to unpark.

     [ETIMEDOUT]
	       The UTC time specified by abstime has passed.

SEE ALSO

     _lwp_unpark(2), _lwp_unpark_all(2), _lwp_wakeup(2)

HISTORY

     The _lwp_park() system call first appeared in NetBSD 5.0.

BSD
								September 25, 2007							       BSD

_lwp_cond_wait(2)						   System Calls 						 _lwp_cond_wait(2)

NAME

       _lwp_cond_wait, _lwp_cond_timedwait, _lwp_cond_reltimedwait - wait on a condition variable

SYNOPSIS

       #include <sys/lwp.h>

       int _lwp_cond_wait(lwp_cond_t *cvp, lwp_mutex_t *mp);

       int _lwp_cond_timedwait(lwp_cond_t *cvp, lwp_mutex_t *mp, timestruc_t *abstime);

       int _lwp_cond_reltimedwait(lwp_cond_t *cvp, lwp_mutex_t *mp, timestruc_t *reltime);

DESCRIPTION

       These  functions  are used to wait for the occurrence of a condition represented by an LWP condition variable. LWP condition variables must
       be initialized to 0 before use.

       The _lwp_cond_wait() function atomically releases the LWP mutex pointed to by mp and causes the calling LWP to block on the  LWP  condition
       variable pointed to by cvp. The blocked LWP may be awakened by _lwp_cond_signal(2), _lwp_cond_broadcast(2), or when interrupted by delivery
       of a signal. Any change in value of a condition associated with the condition variable cannot be inferred by the return of _lwp_cond_wait()
       and any such condition must be re-evaluated.

       The  _lwp_cond_timedwait()  function is similar to _lwp_cond_wait(), except that the calling LWP will not block past the time of day speci-
       fied by abstime. If the time of day becomes greater than abstime, _lwp_cond_timedwait() returns with the error code ETIME.

       The _lwp_cond_reltimedwait() function is similar to _lwp_cond_wait(), except that the calling LWP will not block  past  the  relative  time
       specified  by reltime. If the time of day becomes greater than the starting time of day plus reltime, _lwp_cond_reltimedwait() returns with
       the error code ETIME.

       The _lwp_cond_wait(), _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() functions always return with the mutex locked and  owned  by  the
       calling lightweight process.

RETURN VALUES

       Upon successful completion, 0 is returned. A non-zero value indicates an error.

ERRORS

       If  any of the following conditions are detected, _lwp_cond_wait(), _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() fail and return the
       corresponding value:

       EINVAL	       The cvp argument points to an invalid LWP condition variable or the mp argument points to an invalid LWP mutex.

       EFAULT	       The mp, cvp, or abstime argument points to an illegal address.

       If any of the following conditions occur, _lwp_cond_wait(), _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() fail and return the  corre-
       sponding value:

       EINTR	       The call was interrupted by a signal or fork(2).

       If any of the following conditions occur, _lwp_cond_timedwait() and _lwp_cond_reltimedwait() fail and return the corresponding value:

       ETIME	       The time specified inabstime or reltime has passed.

EXAMPLES

       Example 1: Use the _lwp_cond_wait() function in a loop testing some condition.

       The _lwp_cond_wait() function is normally used in a loop testing some condition, as follows:

       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond;
       (void) _lwp_mutex_lock(&m);
       while (cond == FALSE) {
	       (void) _lwp_cond_wait(&cv, &m);
       }
       (void) _lwp_mutex_unlock(&m);

       Example 2: Use the _lwp_cond_timedwait() function in a loop testing some condition.

       The _lwp_cond_timedwait() function is also normally used in a loop testing some condition. It uses an absolute timeout value as follows:

       timestruc_t to;
       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond, err;
       (void) _lwp_mutex_lock(&m);
       to.tv_sec = time(NULL) + TIMEOUT;
       to.tv_nsec = 0;
       while (cond == FALSE) {
	       err = _lwp_cond_timedwait(&cv, &m, &to);
	       if (err == ETIME) {
		       /* timeout, do something */
		       break;
	       SENDwhom}
       }
       (void) _lwp_mutex_unlock(&m);

       This  example sets a bound on the total wait time even though the _lwp_cond_timedwait() may return several times due to the condition being
       signalled or the wait being interrupted.

       Example 3: Use the _lwp_cond_reltimedwait() function in a loop testing some condition.

       The _lwp_cond_reltimedwait() function is also normally used in a loop testing some condition. It uses a relative timeout value as follows:

       timestruc_t to;
       lwp_mutex_t m;
       lwp_cond_t cv;
       int cond, err;
       (void) _lwp_mutex_lock(&m);
       while (cond == FALSE) {
	       to.tv_sec = TIMEOUT;
	       to.tv_nsec = 0;
	       err = _lwp_cond_reltimedwait(&cv, &m, &to);
	       if (err == ETIME) {
		       /* timeout, do something */
		       break;
	       }
       }
       (void) _lwp_mutex_unlock(&m);

SEE ALSO

       _lwp_cond_broadcast(2), _lwp_cond_signal(2), _lwp_kill(2), _lwp_mutex_lock(2), fork(2), kill(2)

SunOS 5.10							    13 Apr 2001 						 _lwp_cond_wait(2)