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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, 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:

     ⊕   The ts argument is non-NULL, and the time it specifies has passed.
         The ts time can be a relative interval to wait if the flags argument
         does not contain TIMER_ABSTIME or it can be an absolute time.  The
         clock_id argument contains the clock to be used; it can be:
         CLOCK_REALTIME or CLOCK_MONOTONIC.

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

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

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

     If the ts argument contains a relative time interval, it will be modified
     to contain the remaining time to sleep when _lwp_park() returns.

     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 an 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
     The _lwp_park() function may return the value of 0.  Otherwise the value
     -1 is returned and the global variable 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 10.99                     July 30, 2019                    NetBSD 10.99