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NAME ck_sequence_init, ck_sequence_read_begin, ck_sequence_read_retry, ck_sequence_write_begin, ck_sequence_write_end -- sequence locks LIBRARY Concurrency Kit (libck, -lck) SYNOPSIS #include <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 us- ing 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 copy- ing 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 respec- tive 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/ July 26, 2013. ck_sequence(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO
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