---
name: "ck_rwcohort"
section: "3"
platform: "linux"
package: "libck-dev"
version: "0.7.2-6"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/ck_rwcohort"
---

# ck\_rwcohort(3)

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

**#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)](/CK_COHORT_PROTOTYPE/3.md) 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)](/ck_cohort/3.md) 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)](/CK_COHORT_PROTOTYPE/3.md) or the [CK\_COHORT\_TRYLOCK\_PROTOTYPE(3)](/CK_COHORT_TRYLOCK_PROTOTYPE/3.md) macros, and define a reader-writer lock type using the [CK\_RWCOHORT\_PROTOTYPE(3)](/CK_RWCOHORT_PROTOTYPE/3.md) 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_PROTOTYPE/3.md), [CK\_COHORT\_TRYLOCK\_PROTOTYPE(3)](/CK_COHORT_TRYLOCK_PROTOTYPE/3.md), [CK\_COHORT\_INSTANCE(3)](/CK_COHORT_INSTANCE/3.md), CK\_COHORT\_INITIALIZER(3), [CK\_COHORT\_INIT(3)](/CK_COHORT_INIT/3.md), [CK\_COHORT\_LOCK(3)](/CK_COHORT_LOCK/3.md), [CK\_COHORT\_UNLOCK(3)](/CK_COHORT_UNLOCK/3.md), CK\_COHORT\_LOCKED(3), [CK\_COHORT\_TRYLOCK(3)](/CK_COHORT_TRYLOCK/3.md),

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