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Man Pages


Manual Reference Pages  -  CK_SEQUENCE (3)

NAME

ck_sequence_init, ck_sequence_read_begin, ck_sequence_read_retry, ck_sequence_write_begin, ck_sequence_write_end - sequence locks

CONTENTS

Library
Synopsis
Description
Example
See Also

LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS


.In ck_sequence.h

ck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;

void ck_sequence_init ck_sequence_t *sq unsigned int ck_sequence_read_begin const ck_sequence_t *sq bool ck_sequence_read_retry const ck_sequence_t *sq unsigned int version void ck_sequence_write_begin ck_sequence_t *sq void ck_sequence_write_end ck_sequence_t *sq

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 ck_sequence_init. Before readers attempt to read data that may be concurrently modified they must first save the return value of 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 ck_sequence_read_begin to ck_sequence_read_retry. If 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 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 ck_sequence_write_end to indicate that the updates have left respective objects in a consistent state.

EXAMPLE

#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; }

SEE ALSO

ck_brlock(3), ck_bytelock(3), ck_rwlock(3)

Additional information available at http://concurrencykit.org/

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