NAME

ck_ring_dequeue_spsc — dequeue pointer from bounded FIFO

LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS

#include <ck_ring.h>

bool
ck_ring_dequeue_spsc(ck_ring_t *ring, ck_ring_buffer_t *buffer, void *result);

DESCRIPTION

The ck_ring_dequeue_spsc(3) function dequeues a pointer from the bounded buffer pointed to by ring in FIFO fashion. The pointer is stored in the pointer pointed to by result. The buffer pointed to by buffer must be unique to ring and point to an array of ck_ring_buffer_t of sufficient length (according to the power-of-2 elements in the buffer). The decoupling of the ring from the buffer serves to address use-cases involving multiple address spaces and DMA, among others. If you are on non-POSIX platforms or wish for strict compliance with C, then it is recommended to pass a pointer of type void ** for result. This function is safe to call without locking for one concurrent invocation of ck_ring_dequeue_spsc(3) and up to one concurrent ck_ring_enqueue_spsc(3) invocation. This function provides wait-free progress guarantees.

EXAMPLE

#include <ck_ring.h>

/* This ring was previously initialized with ck_ring_init. */
ck_ring_t ring;

/* The ring was initialized for 1023 elements. */
ck_ring_buffer_t buffer[1024];

void
dequeue(void)
{
	void *result;

	/* Dequeue from ring until it is empty. */
	while (ck_ring_dequeue_spsc(&ring, &buffer, &result) == true) {
		/*
		 * Results contains the oldest pointer in ring
		 * since the dequeue operation returned true.
		 */
		operation(result);
	}

	/* An empty ring was encountered, leave. */
	return;
}

RETURN VALUES

The function returns true if the buffer was non-empty. The result of the dequeue operation is stored in the value pointed to by result. The function will return false if the buffer was empty and the value in result will be undefined.