1CK_RING_TRYDEQUEUE_SP... BSD Library Functions Manual CK_RING_TRYDEQUEUE_SP...
2
4 ck_ring_trydequeue_spmc — dequeue from bounded FIFO and allow for spuri‐
5 ous failure
6
8 Concurrency Kit (libck, -lck)
9
11 #include <ck_ring.h>
12 bool
14 ck_ring_trydequeue_spmc(ck_ring_t *ring, ck_ring_buffer_t *buffer,
15 void *result);
16
18 The ck_ring_trydequeue_spmc(3) function attempts to dequeue a pointer
19 from the bounded buffer pointed to by ring in FIFO fashion. The pointer
20 is stored in the pointer pointed to by result. The buffer pointed to by
21 buffer must be unique to ring and point to an array of ck_ring_buffer_t
22 of sufficient length (according to the power-of-2 elements in the buf‐
23 fer). The decoupling of the ring from the buffer serves to address use-
24 cases involving multiple address spaces and DMA, among others. If you
25 are on non-POSIX platforms or wish for strict compliance with C, then it
26 is recommended to pass a pointer of type void ** for result. This func‐
27 tion is safe to call without locking for UINT_MAX concurrent
28 ck_ring_dequeue_spmc(3) or ck_ring_trydequeue_spmc(3) invocations and up
29 to one concurrent ck_ring_enqueue_spmc(3) or ck_ring_tryenqueue_spmc(3)
30 invocation. This operation will always complete in a bounded number of
31 steps. It is possible for the function to return false even if ring is
32 non-empty. This
33
35 #include <ck_ring.h>
36 /* This ring was previously initialized with ck_ring_init. */
38 ck_ring_t ring;
39 /* The ring was initialized for 1023 elements. */
41 ck_ring_buffer_t buffer[1024];
42 void
44 dequeue(void)
45 {
46 void *result;
47 /* Dequeue from ring until contention is actively observed. */
49 while (ck_ring_trydequeue_spmc(&ring, &buffer, &result) == true) {
50 /*
51 * Results contains the oldest pointer in ring
52 * since the dequeue operation returned true.
53 */
54 operation(result);
55 }
56 /* An empty ring was encountered, leave. */
58 return;
59 }
60
62 The function returns true if the dequeue operation completely success‐
63 fully in a bounded number of steps. The result of the dequeue operation
64 is stored in the value pointed to by result. Otherwise, the function
65 will return false if the buffer was empty or if the operation could not
66 be completed in a bounded number of steps. If the function returns false,
67 then the contents of result are undefined.
68
70 ck_ring_init(3), ck_ring_dequeue_spmc(3), ck_ring_enqueue_spmc(3),
71 ck_ring_enqueue_spmc_size(3), ck_ring_dequeue_spsc(3),
72 ck_ring_enqueue_spsc(3), ck_ring_enqueue_spsc_size(3),
73 ck_ring_capacity(3), ck_ring_size(3)
74 Additional information available at http://concurrencykit.org/
76 April 20, 2013