LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS

In ck_ring.h Ft bool Fn ck_ring_trydequeue_spmc ck_ring_t *ring ck_ring_buffer_t *buffer void *result

DESCRIPTION

The Fn ck_ring_trydequeue_spmc 3 function attempts to dequeue a pointer from the bounded buffer pointed to by Fa ring in FIFO fashion. The pointer is stored in the pointer pointed to by Fa result . The buffer pointed to by Fa buffer must be unique to Fa 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 Fa result . This function is safe to call without locking for UINT_MAX concurrent Fn ck_ring_dequeue_spmc 3 or Fn ck_ring_trydequeue_spmc 3 invocations and up to one concurrent Fn ck_ring_enqueue_spmc 3 or Fn 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 Fa 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 Fa 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 Fa result are undefined.