.\"
.\" Copyright 2013 Samy Al Bahra.
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.Dd July 26, 2013.
.Dt ck_brlock 3
.Sh NAME
.Nm ck_brlock
.Nd big-reader locks
.Sh LIBRARY
Concurrency Kit (libck, \-lck)
.Sh SYNOPSIS
.In ck_brlock.h
.Pp
.Dv ck_brlock_t brlock = CK_BRLOCK_INITIALIZER;
.Pp
.Dv ck_brlock_reader_t reader = CK_BRLOCK_READER_INITIALIZER;
.Pp
.Ft void
.Fn ck_brlock_init "ck_brlock_t *br"
.Ft void
.Fn ck_brlock_write_lock "ck_brlock_t *br"
.Ft void
.Fn ck_brlock_write_unlock "ck_brlock_t *br"
.Ft bool
.Fn ck_brlock_write_trylock "ck_brlock_t *br" "unsigned int factor"
.Ft void
.Fn ck_brlock_read_register "ck_brlock_t *br" "ck_brlock_reader_t *reader"
.Ft void
.Fn ck_brlock_read_unregister "ck_brlock_t *br" "ck_brlock_reader_t *reader"
.Ft void
.Fn ck_brlock_read_lock "ck_brlock_t *br" "ck_brlock_reader_t *reader"
.Ft bool
.Fn ck_brlock_read_trylock "ck_brlock_t *br" "ck_brlock_reader_t *reader" \
"unsigned int factor"
.Ft void
.Fn ck_brlock_read_unlock "ck_brlock_reader_t *reader"
.Sh DESCRIPTION
Big reader locks are distributed reader-writer locks with low latency constant time
reader acquisition (with respect to number of concurrent readers). On the other
hand, writer acquisitions are a relatively expensive O(n) operation. This is a write-biased
lock.
.Sh EXAMPLE
.Bd -literal -offset indent
static ck_brlock_t lock = CK_BRLOCK_INITIALIZER;
static __thread ck_brlock_reader_t reader;

static void
reader(void)
{

	/* Add our thread as a lock participant. */
	ck_brlock_read_register(&lock, &reader);

	for (;;) {
		ck_brlock_read_lock(&lock, &reader);
		/* Read-side critical section. */
		ck_brlock_read_unlock(&reader);

		if (ck_brlock_read_trylock(&lock, &reader, 1) == true) {
			/* Read-side critical section. */
			ck_brlock_read_unlock(&reader);
		}
	}

	return;
}

static void
writer(void)
{

	for (;;) {
		ck_brlock_write_lock(&lock);
		/* Write-side critical section. */
		ck_brlock_write_unlock(&lock);

		if (ck_brlock_write_trylock(&lock, 1) == true) {
			/* Write-side critical section. */
			ck_brlock_write_unlock(&lock);
		}
	}

	return;
}
.Ed
.Sh SEE ALSO
.Xr ck_bytelock 3 ,
.Xr ck_rwlock 3
.Pp
Additional information available at http://concurrencykit.org/