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

LIBRARY
     Concurrency Kit (libck, -lck)

SYNOPSIS
     #include <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.

     CK_RWCOHORT_STRATEGY_PROTOTYPE(COHORT_NAME cohort_name);

     CK_RWCOHORT_STRATEGY_NAME(COHORT_NAME cohort_name);

     CK_RWCOHORT_STRATEGY_INSTANCE(COHORT_NAME cohort_name);

     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

     CK_RWCOHORT_STRATEGY_READ_LOCK(COHORT_NAME cohort_name, RWCOHORT lock,
	 COHORT cohort, void *global_context, void *local_context);

     CK_RWCOHORT_STRATEGY_READ_UNLOCK(COHORT_NAME cohort_name, RWCOHORT lock,
	 COHORT cohort, void *global_context, void *local_context);

     CK_RWCOHORT_STRATEGY_WRITE_LOCK(COHORT_NAME cohort_name, RWCOHORT lock,
	 COHORT cohort, void *global_context, void *local_context);

     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_PROTOTYPE(3) 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_PROTOTYPE(3) 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_cohort(3) 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_PROTOTYPE(3) or the CK_COHORT_TRYLOCK_PRO-
     TOTYPE(3) macros, and define a reader-writer lock type using  the	CK_RWCO-
     HORT_PROTOTYPE(3) 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;
	   }

SEE ALSO
     CK_COHORT_PROTOTYPE(3),	CK_COHORT_TRYLOCK_PROTOTYPE(3),    CK_COHORT_IN-
     STANCE(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/

				 April 23, 2013.		  ck_rwcohort(3)

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