ck/doc/ck_rwcohort

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.Dd February 24, 2013.
.Dt ck_cohort 3
.Sh NAME
.Nm ck_cohort
.Nd generalized interface for lock cohorts
.Sh LIBRARY
Concurrency Kit (libck, \-lck)
.Sh SYNOPSIS
.In ck_cohort.h
.Fn CK_COHORT_PROTOTYPE "COHORT_NAME cohort_name" "LOCK_FXN global_lock_method" \
"LOCK_FXN global_unlock_method" "LOCK_FXN local_lock_method" "LOCK_FXN local_unlock_method"
.Fn CK_COHORT_TRYLOCK_PROTOTYPE "COHORT_NAME cohort_name" \
"LOCK_FXN global_lock_method" "LOCK_FXN global_unlock_method" \
"BOOL_LOCK_FXN global_locked_method" BOOL_LOCK_FXN global_trylock_method" \
"LOCK_FXN local_lock_method" "LOCK_FXN local_unlock_method" \
"BOOL_LOCK_FXN local_locked_method" BOOL_LOCK_FXN local_trylock_method"
.Fn CK_COHORT_INSTANCE "COHORT_NAME cohort_name"
.Fn CK_COHORT_INIT "COHORT_NAME cohort_name" "ck_cohort *cohort" \
"void *global_lock" "void *local_lock" "unsigned int pass_limit"
.Fn CK_COHORT_LOCK "COHORT_NAME cohort_name" "ck_cohort *cohort" \
"void *global_context" "void *local_context"
.Fn CK_COHORT_UNLOCK "COHORT_NAME cohort_name" "ck_cohort *cohort" \
"void *global_context" "void *local_context"
.Pp
Where LOCK_FXN refers to a method with the signature
.br
void(void *lock, void *context)
.br
BOOL_LOCK_FXN refers to a method with the signature
.br
bool(void *lock, void *context)
.Pp
The
.Fa context 
argument in each signature is used to pass along any additional information that
the lock might need for its lock, unlock and trylock methods.  The values for this
argument are provided to each call to
.Xr CK_COHORT_LOCK 3 ,
.Xr CK_COHORT_UNLOCK 3 ,
.Xr CK_COHORT_LOCKED 3 ,
and
.Xr CK_COHORT_TRYLOCK 3
.
.Sh DESCRIPTION
ck_cohort.h provides an interface for defining lock cohorts with
arbitrary lock types.  Cohorts are a mechanism for coordinating
threads on NUMA architectures in order to reduce the frequency
with which a lock is passed between threads on different clusters.
.Pp
Before using a cohort, the user must define a cohort type using
either the
.Fn CK_COHORT_PROTOTYPE
or the
.Fn CK_COHORT_TRYLOCK_PROTOTYPE
macros.  These macros allow the user to specify the lock methods that
they would like the cohort to use.  See the
.Xr CK_COHORT_PROTOTYPE 3
and
.Xr CK_COHORT_TRYLOCK_PROTOTYPE 3
man pages for more details.
.Pp
.Sh EXAMPLE
.Bd -literal -offset indent
#include <stdlib.h>
#include <pthread.h>

#include <ck_pr.h>
#include <ck_cohort.h>
#include <ck_spinlock.h>

/* 
 * Create cohort methods with signatures that match
 * the required signature
 */
static void
ck_spinlock_lock_with_context(ck_spinlock_t *lock, void *context)
{
	(void)context;
	ck_spinlock_lock(lock);
	return;
}

static void
ck_spinlock_unlock_with_context(ck_spinlock_t *lock, void *context)
{
	(void)context;
	ck_spinlock_unlock(lock);
	return;
}

static bool
ck_spinlock_locked_with_context(ck_spinlock_t *lock, void *context)
{
	(void)context;
	return ck_spinlock_locked(lock);
}

/*
 * define a cohort type named "test_cohort" that will use
 * the above methods for both its global and local locks
 */
CK_COHORT_PROTOTYPE(test_cohort,
	ck_spinlock_lock_with_context, ck_spinlock_unlock_with_context, ck_spinlock_locked_with_context
	ck_spinlock_lock_with_context, ck_spinlock_unlock_with_context, ck_spinlock_locked_with_context)

static ck_spinlock_t global_lock = CK_SPINLOCK_INITIALIZER;
static unsigned int ready;

static void *
function(void *context)
{
	CK_COHORT_INSTANCE(test_cohort) *cohort = context;

	while (ready == 0);

	while (ready > 0) {
		/*
		 * acquire the cohort lock before performing critical section.
		 * note that we pass NULL for both the global and local context
		 * arguments because neither the lock nor unlock functions
		 * will use them.
		 */
		CK_COHORT_LOCK(test_cohort, cohort, NULL, NULL);

		/* perform critical section */

		/* relinquish cohort lock */
		CK_COHORT_UNLOCK(test_cohort, cohort, NULL, NULL);
	}

	return NULL;
}

int
main(void)
{
	unsigned int nthr = 4;
	unsigned int n_cohorts = 2;
	unsigned int i;

	/* allocate 2 cohorts of the defined type */
	CK_COHORT_INSTANCE(test_cohort) *cohorts =
	    calloc(n_cohorts, sizeof(CK_COHORT_INSTANCE(test_cohort)));

	/* create local locks to use with each cohort */
	ck_spinlock_t *local_locks = 
		calloc(n_cohorts, sizeof(ck_spinlock_t));

	pthread_t *threads =
		calloc(nthr, sizeof(pthread_t));

	/* initialize each of the cohorts before using them */
	for (i = 0 ; i < n_cohorts ; ++i) {
		CK_COHORT_INIT(test_cohort, cohorts + i, &global_lock, local_locks + i,
			CK_COHORT_DEFAULT_LOCAL_PASS_LIMIT);
	}

	/* start each thread and assign cohorts equally */
	for (i = 0 ; i < nthr ; ++i) {
		pthread_create(threads + i, NULL, function, cohorts + (i % n_cohorts));
	}

	ck_pr_store_uint(&ready, 1);
	sleep(10);
	ck_pr_store_uint(&ready, 0);

	for (i = 0 ; i < nthr ; ++i) {
		pthread_join(threads[i], NULL);
	}

	return 0;
}
.Ed
.Sh SEE ALSO
.Xr CK_COHORT_PROTOTYPE 3 ,
.Xr CK_COHORT_TRYLOCK_PROTOTYPE 3 ,
.Xr CK_COHORT_INSTANCE 3 ,
.Xr CK_COHORT_INITIALIZER 3 ,
.Xr CK_COHORT_INIT 3 ,
.Xr CK_COHORT_LOCK 3 ,
.Xr CK_COHORT_UNLOCK 3 ,
.Xr CK_COHORT_LOCKED 3 ,
.Xr CK_COHORT_TRYLOCK 3 ,
.Pp
Additional information available at http://concurrencykit.org/