PCQ(9)							   BSD Kernel Developer's Manual						    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 con-
	      current 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.

BSD
								 January 22, 2012							       BSD