ck_rwcohort (3) - Linux Manuals

ck_rwcohort: generalized interface for reader-writer locks using cohort locks

NAME

ck_rwcohort - generalized interface for reader-writer locks using cohort locks

LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS

In ck_rwcohort.h In each of the following macros, "STRATEGY" should be replaced with either "NEUTRAL", "RP", or "WP" depending on which locking strategy the user prefers. RP and WP represent reader preference and writer preference, respectively, while NEUTRAL represents a strategy neutral to reads vs. writes. Fn CK_RWCOHORT_STRATEGY_PROTOTYPE COHORT_NAME cohort_name Fn CK_RWCOHORT_STRATEGY_NAME COHORT_NAME cohort_name Fn CK_RWCOHORT_STRATEGY_INSTANCE COHORT_NAME cohort_name Fn CK_RWCOHORT_STRATEGY_INIT COHORT_NAME cohort_name RWCOHORT lock unsigned int wait_limit Note: the wait_limit argument should be omitted for locks using the neutral strategy Fn CK_RWCOHORT_STRATEGY_READ_LOCK COHORT_NAME cohort_name RWCOHORT lock COHORT cohort void *global_context void *local_context Fn CK_RWCOHORT_STRATEGY_READ_UNLOCK COHORT_NAME cohort_name RWCOHORT lock COHORT cohort void *global_context void *local_context Fn CK_RWCOHORT_STRATEGY_WRITE_LOCK COHORT_NAME cohort_name RWCOHORT lock COHORT cohort void *global_context void *local_context Fn CK_RWCOHORT_STRATEGY_WRITE_UNLOCK COHORT_NAME cohort_name RWCOHORT lock COHORT cohort void *global_context void *local_context

Arguments of type RWCOHORT must be pointers to structs defined using the CK_RWCOHORT_STRATEGY_PROTOTYPE3 macro with the same strategy and cohort name as the current call.

Arguments of type COHORT must be pointers to structs defined using the CK_COHORT_PROTOTYPE3 macro.

DESCRIPTION

ck_rwcohort.h provides an interface for defining reader-writer locks that use cohort locks internally to increase performance on NUMA architectures. See ck_cohort3 for more information about cohort locks.

Before using a reader-writer cohort lock, the user must define a cohort type using either the CK_COHORT_PROTOTYPE3 or the CK_COHORT_TRYLOCK_PROTOTYPE3 macros, and define a reader-writer lock type using the CK_RWCOHORT_PROTOTYPE3 macro.

EXAMPLE

#include <stdlib.h>
#include <pthread.h>

#include <ck_pr.h>
#include <ck_cohort.h>
#include <ck_rwcohort.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)

/* define a reader-writer type using the same cohort type */
CK_RWCOHORT_WP_PROTOTYPE(test_cohort)

static ck_spinlock_t global_lock = CK_SPINLOCK_INITIALIZER;
static CK_COHORT_INSTANCE(test_cohort) *cohorts;
static CK_RWCOHORT_WP_INSTANCE(test_cohort) rw_cohort = CK_RWCOHORT_WP_INITIALIZER;
static unsigned int ready;

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

        while (ck_pr_load_uint(&ready) == 0);

        while (ck_pr_load_uint(&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;
}