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diff --git a/doc/ck_sequence b/doc/ck_sequence new file mode 100644 index 0000000..faa1631 --- /dev/null +++ b/doc/ck_sequence @@ -0,0 +1,144 @@ +.\" +.\" 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_init , +.Nm ck_sequence_read_begin , +.Nm ck_sequence_read_retry , +.Nm ck_sequence_write_begin , +.Nm ck_sequence_write_end +.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 "const ck_sequence_t *sq" +.Ft bool +.Fn ck_sequence_read_retry "const 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. + */ + do { + version = ck_sequence_read_begin(&seqlock); + copy = global; + } while (ck_sequence_read_retry(&seqlock, version)); + + /* + * The previous may also be expressed using CK_SEQUENCE_READ. + * Generally recommend to only use ck_sequence_read_retry + * if you would like to detect a conflicting write at some + * higher granularity. + */ + CK_SEQUENCE_READ(&seqlock, &version) { + copy = global; + } + + 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_brlock 3 , +.Xr ck_bytelock 3 , +.Xr ck_rwlock 3 +.Pp +Additional information available at http://concurrencykit.org/ |