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:
- 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.
- 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().
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.