PCQ(9)

NAME
pcq - producer/consumer queue

SYNOPSIS
#include <sys/pcq.h>
pcq_t *
pcq_create(size_t maxlen, km_flags_t kmflags);
void
pcq_destroy(pcq_t *pcq);
void *
pcq_get(pcq_t *pcq);
size_t
pcq_maxitems(pcq_t *pcq);
void *
pcq_peek(pcq_t *pcq);
bool
pcq_put(pcq_t *pcq, void *item);

DESCRIPTION
The machine-independent pcq interface provides lockless producer/consumer queues. A queue ( pcq_t) allows multiple writers (producers), but only a single reader (consumer). The consumer is expected to be protected by a lock that covers the structure that the pcq_t is embedded into ( e.g., socket lock, ifnet hwlock). These queues operate in a first-in, first-out (FIFO) manner. The act of inserting or removing an item from a pcq_t does not modify the item in any way. pcq does not prevent an item from being inserted multiple times into a single pcq_t.

FUNCTIONS

pcq_create(maxlen, kmflags)
    Create a queue that can store at most maxlen items at one time. kmflags should be either KM_SLEEP, if pcq_create() is allowed to sleep until resources are available, or KM_NOSLEEP if it should return NULL immediately, if resources are unavailable.

pcq_destroy(pcq)
    Free the resources held by pcq.

pcq_get(pcq)
    Remove the next item to be consumed from the queue and return it. If the queue is empty, return NULL. The caller must prevent concurrent gets from occuring.

pcq_maxitems(pcq)
    Return the maximum number of items that the queue can store at any one time.

pcq_peek(pcq)
    Return the next item to be consumed from the queue but do not remove it from the queue. If the queue is empty, return NULL.

pcq_put(pcq, item)
    Place an item at the end of the queue. If there is no room in the queue for the item, return false; otherwise, return true. The item must not have the value of NULL.

CODE REFERENCES
The pcq interface is implemented within the file sys/kern/subr_pcq.c.

SEE ALSO
atomic_ops(3), queue(9)

HISTORY
The pcq interface first appeared in NetBSD 6.0.