NAME

ck_ring_trydequeue_spmc — dequeue from bounded FIFO and allow for spurious failure

LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS

#include <ck_ring.h>

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

DESCRIPTION

The ck_ring_trydequeue_spmc(3) function attempts to dequeue 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 UINT_MAX concurrent ck_ring_dequeue_spmc(3) or ck_ring_trydequeue_spmc(3) invocations and up to one concurrent ck_ring_enqueue_spmc(3) or ck_ring_tryenqueue_spmc(3) invocation. This operation will always complete in a bounded number of steps. It is possible for the function to return false even if ring is non-empty. This

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 contention is actively observed. */
	while (ck_ring_trydequeue_spmc(&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 dequeue operation completely successfully in a bounded number of steps. The result of the dequeue operation is stored in the value pointed to by result. Otherwise, the function will return false if the buffer was empty or if the operation could not be completed in a bounded number of steps. If the function returns false, then the contents of result are undefined.