DragonFly On-Line Manual Pages

CK_RING_TRYDEQUEUE_SPMC(3)                  DragonFly Library Functions Manual

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.

SEE ALSO
     ck_ring_init(3), ck_ring_dequeue_spmc(3), ck_ring_enqueue_spmc(3),
     ck_ring_enqueue_spmc_size(3), ck_ring_dequeue_spsc(3),
     ck_ring_enqueue_spsc(3), ck_ring_enqueue_spsc_size(3),
     ck_ring_capacity(3), ck_ring_size(3)

     Additional information available at http://concurrencykit.org/

                                April 20, 2013