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_LWP_PARK(2)                  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(clockid_t clock_id, int flags, const struct timespec *ts,
         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 interruptably
     in the kernel, until one of the following conditions is met:

     o   The ts argument is non-NULL, and the time it specifies has passed.
         The ts time can be an relative interval to wait if the flags argument
         does not contain TIMER_ABSTIME or it can be an absolute time compared
         to CLOCK_REALTIME or CLOCK_MONOTONIC depending on the value of the
         clock_id argument.

     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 ts is invalid.

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

     [ETIMEDOUT]
               The UTC time specified by ts 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.

NetBSD 7.1.2                    March 28, 2013                    NetBSD 7.1.2