NAME

     ck_cohort — generalized interface for lock cohorts

LIBRARY

     Concurrency Kit (libck, -lck)

SYNOPSIS

     #include <ck_cohort.h>

     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);

     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);

     CK_COHORT_INSTANCE(COHORT_NAME cohort_name);

     CK_COHORT_INIT(COHORT_NAME cohort_name, ck_cohort *cohort, void *global_lock,
         void *local_lock, unsigned int pass_limit);

     CK_COHORT_LOCK(COHORT_NAME cohort_name, ck_cohort *cohort, void *global_context,
         void *local_context);

     CK_COHORT_UNLOCK(COHORT_NAME cohort_name, ck_cohort *cohort, void *global_context,
         void *local_context);

     Where LOCK_FXN refers to a method with the signature
     void(void *lock, void *context)
     BOOL_LOCK_FXN refers to a method with the signature
     bool(void *lock, void *context)

     The 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 CK_COHORT_LOCK(3), CK_COHORT_UNLOCK(3), CK_COHORT_LOCKED(3), and
     CK_COHORT_TRYLOCK(3)

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.

     Before using a cohort, the user must define a cohort type using either the
     CK_COHORT_PROTOTYPE() or the 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
     CK_COHORT_PROTOTYPE(3) and CK_COHORT_TRYLOCK_PROTOTYPE(3) man pages for more details.

EXAMPLE

           #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;
           }

SEE ALSO

     CK_COHORT_PROTOTYPE(3), CK_COHORT_TRYLOCK_PROTOTYPE(3), CK_COHORT_INSTANCE(3),
     CK_COHORT_INITIALIZER(3), CK_COHORT_INIT(3), CK_COHORT_LOCK(3), CK_COHORT_UNLOCK(3),
     CK_COHORT_LOCKED(3), CK_COHORT_TRYLOCK(3),

     Additional information available at http://concurrencykit.org/

                                        February 24, 2013.