Other Alias
ck_sequence_init, ck_sequence_read_begin, 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;
}