pcq(9) - NetBSD Manual Pages

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PCQ(9)                 NetBSD Kernel Developer's Manual                 PCQ(9)

pcq -- producer/consumer queue
#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);
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.
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 pre- vent concurrent gets from occurring. 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.
The pcq interface is implemented within the file sys/kern/subr_pcq.c.
atomic_ops(3), queue(3)
The pcq interface first appeared in NetBSD 6.0. NetBSD 9.1 January 22, 2012 NetBSD 9.1
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