/*
* Attach to shared memory message queues.
*
* We use our worker number to determine to which queue we should attach.
* The queues are registered at keys 1..<number-of-workers>. The user backend
* writes to queue #1 and reads from queue #<number-of-workers>; each worker
* reads from the queue whose number is equal to its worker number and writes
* to the next higher-numbered queue.
*/
static void
attach_to_queues(dsm_segment *seg, shm_toc *toc, int myworkernumber,
shm_mq_handle **inqhp, shm_mq_handle **outqhp)
{
shm_mq *inq;
shm_mq *outq;
inq = shm_toc_lookup(toc, myworkernumber);
shm_mq_set_receiver(inq, MyProc);
*inqhp = shm_mq_attach(inq, seg, NULL);
outq = shm_toc_lookup(toc, myworkernumber + 1);
shm_mq_set_sender(outq, MyProc);
*outqhp = shm_mq_attach(outq, seg, NULL);
}
/*
* Set up a dynamic shared memory segment.
*
* We set up a small control region that contains only a test_shm_mq_header,
* plus one region per message queue. There are as many message queues as
* the number of workers, plus one.
*/
static void
setup_dynamic_shared_memory(int64 queue_size, int nworkers,
dsm_segment **segp, test_shm_mq_header **hdrp,
shm_mq **outp, shm_mq **inp)
{
shm_toc_estimator e;
int i;
Size segsize;
dsm_segment *seg;
shm_toc *toc;
test_shm_mq_header *hdr;
/* Ensure a valid queue size. */
if (queue_size < 0 || ((uint64) queue_size) < shm_mq_minimum_size)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("queue size must be at least %zu bytes",
shm_mq_minimum_size)));
if (queue_size != ((Size) queue_size))
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("queue size overflows size_t")));
/*
* Estimate how much shared memory we need.
*
* Because the TOC machinery may choose to insert padding of oddly-sized
* requests, we must estimate each chunk separately.
*
* We need one key to register the location of the header, and we need
* nworkers + 1 keys to track the locations of the message queues.
*/
shm_toc_initialize_estimator(&e);
shm_toc_estimate_chunk(&e, sizeof(test_shm_mq_header));
for (i = 0; i <= nworkers; ++i)
shm_toc_estimate_chunk(&e, (Size) queue_size);
shm_toc_estimate_keys(&e, 2 + nworkers);
segsize = shm_toc_estimate(&e);
/* Create the shared memory segment and establish a table of contents. */
seg = dsm_create(shm_toc_estimate(&e), 0);
toc = shm_toc_create(PG_TEST_SHM_MQ_MAGIC, dsm_segment_address(seg),
segsize);
/* Set up the header region. */
hdr = shm_toc_allocate(toc, sizeof(test_shm_mq_header));
SpinLockInit(&hdr->mutex);
hdr->workers_total = nworkers;
hdr->workers_attached = 0;
hdr->workers_ready = 0;
shm_toc_insert(toc, 0, hdr);
/* Set up one message queue per worker, plus one. */
for (i = 0; i <= nworkers; ++i)
{
shm_mq *mq;
mq = shm_mq_create(shm_toc_allocate(toc, (Size) queue_size),
(Size) queue_size);
shm_toc_insert(toc, i + 1, mq);
if (i == 0)
{
/* We send messages to the first queue. */
shm_mq_set_sender(mq, MyProc);
*outp = mq;
}
if (i == nworkers)
{
/* We receive messages from the last queue. */
shm_mq_set_receiver(mq, MyProc);
*inp = mq;
}
}
/* Return results to caller. */
*segp = seg;
*hdrp = hdr;
}