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.\"
.\" Copyright 2014 Samy Al Bahra.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"
.Dd April 22, 2014.
.Dt ck_swlock 3
.Sh NAME
.Nm ck_swlock_init ,
.Nm ck_swlock_write_latch ,
.Nm ck_swlock_write_unlatch ,
.Nm ck_swlock_write_lock ,
.Nm ck_swlock_write_unlock ,
.Nm ck_swlock_write_trylock ,
.Nm ck_swlock_write_downgrade ,
.Nm ck_swlock_locked_writer ,
.Nm ck_swlock_read_lock ,
.Nm ck_swlock_read_trylock ,
.Nm ck_swlock_read_unlock ,
.Nm ck_swlock_locked_reader
.Nd centralized copy-safe write-biased single-writer read-write locks
.Sh LIBRARY
Concurrency Kit (libck, \-lck)
.Sh SYNOPSIS
.In ck_swlock.h
.Pp
.Dv ck_swlock_t lock = CK_SWLOCK_INITIALIZER;
.Pp
.Ft void
.Fn ck_swlock_init "ck_swlock_t *lock"
.Ft void
.Fn ck_swlock_write_lock "ck_swlock_t *lock"
.Ft void
.Fn ck_swlock_write_unlock "ck_swlock_t *lock"
.Ft void
.Fn ck_swlatch_write_latch "ck_swlatch_t *latch"
.Ft void
.Fn ck_swlatch_write_unlatch "ck_swlatch_t *latch"
.Ft bool
.Fn ck_swlock_write_trylock "ck_swlock_t *lock"
.Ft bool
.Fn ck_swlock_write_downgrade "ck_swlock_t *lock"
.Ft bool
.Fn ck_swlock_locked_writer "ck_swlock_t *lock"
.Ft void
.Fn ck_swlock_read_lock "ck_swlock_t *lock"
.Ft bool
.Fn ck_swlock_read_trylock "ck_swlock_t *lock"
.Ft void
.Fn ck_swlock_read_unlock "ck_swlock_t *lock"
.Ft bool
.Fn ck_swlock_locked_reader "ck_swlock_t *lock"
.Sh DESCRIPTION
This is a centralized write-biased single-writer reader-writer lock. It
requires half the space that ck_rwlock does and has a low latency
fast path. The lock supports latch and unlatch operations that
allow it to be used in a copy-safe manner (reader-bits may be
over-written safely).
.Sh EXAMPLE
.Bd -literal -offset indent
#include <ck_swlock.h>
static ck_swlock_t lock = CK_SWLOCK_INITIALIZER;
static void
reader(void)
{
for (;;) {
ck_swlock_read_lock(&lock);
/* Read-side critical section. */
ck_swlock_read_unlock(&lock);
if (ck_swlock_read_trylock(&lock) == true) {
/* Read-side critical section. */
ck_swlock_read_unlock(&lock);
}
}
return;
}
static void
writer(void)
{
ck_swlock_t contrived;
for (;;) {
ck_swlock_write_lock(&lock);
/* Write-side critical section. */
ck_swlock_write_unlock(&lock);
if (ck_swlock_write_trylock(&lock) == true) {
/* Write-side critical section. */
ck_swlock_write_unlock(&lock);
}
ck_swlock_write_latch(&lock);
/* Write-side critical section. */
/* This is safe to do with-in a latch. */
contrived = lock;
lock = contrived;
ck_swlock_write_unlatch(&lock);
}
return;
}
.Ed
.Sh SEE ALSO
.Xr ck_brlock 3 ,
.Xr ck_elide 3 ,
.Xr ck_pflock 3 ,
.Xr ck_rwlock 3 ,
.Xr ck_tflock 3
.Pp
Additional information available at http://concurrencykit.org/
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