Other Alias
ck_sequence_init, ck_sequence_read_retry, ck_sequence_write_begin, ck_sequence_write_endLIBRARY
Concurrency Kit (libck, -lck)SYNOPSIS
In ck_sequence.hck_sequence_t seqlock = CK_SEQUENCE_INITIALIZER;
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
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.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; }