You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
134 lines
4.1 KiB
134 lines
4.1 KiB
.\"
|
|
.\" Copyright 2013 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 July 26, 2013.
|
|
.Dt ck_sequence 3
|
|
.Sh NAME
|
|
.Nm ck_sequence
|
|
.Nd sequence locks
|
|
.Sh LIBRARY
|
|
Concurrency Kit (libck, \-lck)
|
|
.Sh SYNOPSIS
|
|
.In ck_sequence.h
|
|
.Pp
|
|
.Dv ck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;
|
|
.Pp
|
|
.Ft void
|
|
.Fn ck_sequence_init "ck_sequence_t *sq"
|
|
.Ft unsigned int
|
|
.Fn ck_sequence_read_begin "ck_sequence_t *sq"
|
|
.Ft bool
|
|
.Fn ck_sequence_read_retry "ck_sequence_t *sq" "unsigned int version"
|
|
.Ft void
|
|
.Fn ck_sequence_write_begin "ck_sequence_t *sq"
|
|
.Ft void
|
|
.Fn ck_sequence_write_end "ck_sequence_t *sq"
|
|
.Sh DESCRIPTION
|
|
It is recommended to use ck_sequence when a small amount of data that cannot be
|
|
accessed atomically has to be synchronized with readers in a fashion that does
|
|
not block any writer. Readers are able to execute their read-side critical
|
|
sections without any atomic operations. A ck_sequence_t must be initialized
|
|
before use. It may be initialized using either a static initializer
|
|
(CK_SEQUENCE_INITIALIZER) or using
|
|
.Fn ck_sequence_init .
|
|
Before readers attempt to
|
|
read data that may be concurrently modified they must first save the return
|
|
value of
|
|
.Fn ck_sequence_read_begin .
|
|
While or after a reader has completed copying
|
|
the data associated with a ck_sequence_t it must pass the earlier return value
|
|
of
|
|
.Fn ck_sequence_read_begin
|
|
to
|
|
.Fn ck_sequence_read_retry. If
|
|
.Fn ck_sequence_read_retry
|
|
returns true then the copy of data may be inconsistent and the read process
|
|
must be retried. Writers must rely on their own synchronization primitives.
|
|
Once a writer has entered its respective critical section, it must call
|
|
.Fn ck_sequence_write_begin
|
|
to signal intent to update the data protected
|
|
by the ck_sequence_t. Before the writer leaves its critical section it must
|
|
execute
|
|
.Fn ck_sequence_write_end
|
|
to indicate that the updates have left respective objects in a consistent state.
|
|
.Sh EXAMPLE
|
|
.Bd -literal -offset indent
|
|
#include <ck_sequence.h>
|
|
#include <stdlib.h>
|
|
|
|
static struct example {
|
|
int a;
|
|
int b;
|
|
int c;
|
|
} global;
|
|
|
|
static ck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;
|
|
|
|
void
|
|
reader(void)
|
|
{
|
|
struct example copy;
|
|
unsigned int version;
|
|
|
|
/*
|
|
* Attempt a read of the data structure. If the structure
|
|
* has been modified between ck_sequence_read_begin and
|
|
* ck_sequence_read_retry then attempt another read since
|
|
* the data may be in an inconsistent state.
|
|
*/
|
|
CK_SEQUENCE_READ(&seqlock, &version) {
|
|
copy = global;
|
|
}
|
|
|
|
do {
|
|
version = ck_sequence_read_begin(&seqlock);
|
|
copy = global;
|
|
} while (ck_sequence_read_retry(&seqlock, version));
|
|
|
|
return;
|
|
}
|
|
|
|
void
|
|
writer(void)
|
|
{
|
|
|
|
for (;;) {
|
|
ck_sequence_write_begin(&seqlock);
|
|
global.a = rand();
|
|
global.b = global.a + global.b;
|
|
global.c = global.b + global.c;
|
|
ck_sequence_write_end(&seqlock);
|
|
}
|
|
|
|
return;
|
|
}
|
|
.Ed
|
|
.Sh SEE ALSO
|
|
.Xr ck_bytelock 3 ,
|
|
.Xr ck_rwlock 3
|
|
.Pp
|
|
Additional information available at http://concurrencykit.org/
|