/*
* Write a message into a shared message queue.
*
* When nowait = false, we'll wait on our process latch when the ring buffer
* fills up, and then continue writing once the receiver has drained some data.
* The process latch is reset after each wait.
*
* When nowait = true, we do not manipulate the state of the process latch;
* instead, if the buffer becomes full, we return SHM_MQ_WOULD_BLOCK. In
* this case, the caller should call this function again, with the same
* arguments, each time the process latch is set. (Once begun, the sending
* of a message cannot be aborted except by detaching from the queue; changing
* the length or payload will corrupt the queue.)
*/
shm_mq_result
shm_mq_send(shm_mq_handle *mqh, Size nbytes, void *data, bool nowait)
{
shm_mq_result res;
shm_mq *mq = mqh->mqh_queue;
Size bytes_written;
Assert(mq->mq_sender == MyProc);
/* Try to write, or finish writing, the length word into the buffer. */
while (!mqh->mqh_length_word_complete)
{
Assert(mqh->mqh_partial_bytes < sizeof(Size));
res = shm_mq_send_bytes(mqh, sizeof(Size) - mqh->mqh_partial_bytes,
((char *) &nbytes) + mqh->mqh_partial_bytes,
nowait, &bytes_written);
mqh->mqh_partial_bytes += bytes_written;
if (res != SHM_MQ_SUCCESS)
return res;
if (mqh->mqh_partial_bytes >= sizeof(Size))
{
Assert(mqh->mqh_partial_bytes == sizeof(Size));
mqh->mqh_partial_bytes = 0;
mqh->mqh_length_word_complete = true;
}
/* Length word can't be split unless bigger than required alignment. */
Assert(mqh->mqh_length_word_complete || sizeof(Size) > MAXIMUM_ALIGNOF);
}
/* Write the actual data bytes into the buffer. */
Assert(mqh->mqh_partial_bytes <= nbytes);
res = shm_mq_send_bytes(mqh, nbytes - mqh->mqh_partial_bytes,
((char *) data) + mqh->mqh_partial_bytes,
nowait, &bytes_written);
if (res == SHM_MQ_WOULD_BLOCK)
mqh->mqh_partial_bytes += bytes_written;
else
{
mqh->mqh_partial_bytes = 0;
mqh->mqh_length_word_complete = false;
}
if (res != SHM_MQ_SUCCESS)
return res;
/* Notify receiver of the newly-written data, and return. */
return shm_mq_notify_receiver(mq);
}
/*
* Write bytes into a shared message queue.
*/
static shm_mq_result
shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, void *data, bool nowait,
Size *bytes_written)
{
shm_mq *mq = mqh->mqh_queue;
Size sent = 0;
uint64 used;
Size ringsize = mq->mq_ring_size;
Size available;
while (sent < nbytes)
{
bool detached;
uint64 rb;
/* Compute number of ring buffer bytes used and available. */
rb = shm_mq_get_bytes_read(mq, &detached);
Assert(mq->mq_bytes_written >= rb);
used = mq->mq_bytes_written - rb;
Assert(used <= ringsize);
available = Min(ringsize - used, nbytes - sent);
/* Bail out if the queue has been detached. */
if (detached)
return SHM_MQ_DETACHED;
if (available == 0)
{
shm_mq_result res;
/*
* The queue is full, so if the receiver isn't yet known to be
* attached, we must wait for that to happen.
*/
if (!mqh->mqh_counterparty_attached)
{
if (nowait)
{
if (shm_mq_get_receiver(mq) == NULL)
return SHM_MQ_WOULD_BLOCK;
}
else if (!shm_mq_wait_internal(mq, &mq->mq_receiver,
mqh->mqh_handle))
{
mq->mq_detached = true;
return SHM_MQ_DETACHED;
}
mqh->mqh_counterparty_attached = true;
}
/* Let the receiver know that we need them to read some data. */
res = shm_mq_notify_receiver(mq);
if (res != SHM_MQ_SUCCESS)
{
*bytes_written = sent;
return res;
}
/* Skip manipulation of our latch if nowait = true. */
if (nowait)
{
*bytes_written = sent;
return SHM_MQ_WOULD_BLOCK;
}
/*
* Wait for our latch to be set. It might already be set for
* some unrelated reason, but that'll just result in one extra
* trip through the loop. It's worth it to avoid resetting the
* latch at top of loop, because setting an already-set latch is
* much cheaper than setting one that has been reset.
*/
WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
/* An interrupt may have occurred while we were waiting. */
CHECK_FOR_INTERRUPTS();
/* Reset the latch so we don't spin. */
ResetLatch(&MyProc->procLatch);
}
else
{
Size offset = mq->mq_bytes_written % (uint64) ringsize;
Size sendnow = Min(available, ringsize - offset);
/* Write as much data as we can via a single memcpy(). */
memcpy(&mq->mq_ring[mq->mq_ring_offset + offset],
(char *) data + sent, sendnow);
sent += sendnow;
/*
* Update count of bytes written, with alignment padding. Note
* that this will never actually insert any padding except at the
* end of a run of bytes, because the buffer size is a multiple of
* MAXIMUM_ALIGNOF, and each read is as well.
*/
Assert(sent == nbytes || sendnow == MAXALIGN(sendnow));
shm_mq_inc_bytes_written(mq, MAXALIGN(sendnow));
/*
* For efficiency, we don't set the reader's latch here. We'll
* do that only when the buffer fills up or after writing an
* entire message.
*/
}
}
*bytes_written = sent;
return SHM_MQ_SUCCESS;
}
/*
* Write a message into a shared message queue, gathered from multiple
* addresses.
*
* When nowait = false, we'll wait on our process latch when the ring buffer
* fills up, and then continue writing once the receiver has drained some data.
* The process latch is reset after each wait.
*
* When nowait = true, we do not manipulate the state of the process latch;
* instead, if the buffer becomes full, we return SHM_MQ_WOULD_BLOCK. In
* this case, the caller should call this function again, with the same
* arguments, each time the process latch is set. (Once begun, the sending
* of a message cannot be aborted except by detaching from the queue; changing
* the length or payload will corrupt the queue.)
*/
shm_mq_result
shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
{
shm_mq_result res;
shm_mq *mq = mqh->mqh_queue;
Size nbytes = 0;
Size bytes_written;
int i;
int which_iov = 0;
Size offset;
Assert(mq->mq_sender == MyProc);
/* Compute total size of write. */
for (i = 0; i < iovcnt; ++i)
nbytes += iov[i].len;
/* Try to write, or finish writing, the length word into the buffer. */
while (!mqh->mqh_length_word_complete)
{
Assert(mqh->mqh_partial_bytes < sizeof(Size));
res = shm_mq_send_bytes(mqh, sizeof(Size) - mqh->mqh_partial_bytes,
((char *) &nbytes) +mqh->mqh_partial_bytes,
nowait, &bytes_written);
mqh->mqh_partial_bytes += bytes_written;
if (res != SHM_MQ_SUCCESS)
return res;
if (mqh->mqh_partial_bytes >= sizeof(Size))
{
Assert(mqh->mqh_partial_bytes == sizeof(Size));
mqh->mqh_partial_bytes = 0;
mqh->mqh_length_word_complete = true;
}
/* Length word can't be split unless bigger than required alignment. */
Assert(mqh->mqh_length_word_complete || sizeof(Size) > MAXIMUM_ALIGNOF);
}
/* Write the actual data bytes into the buffer. */
Assert(mqh->mqh_partial_bytes <= nbytes);
offset = mqh->mqh_partial_bytes;
do
{
Size chunksize;
/* Figure out which bytes need to be sent next. */
if (offset >= iov[which_iov].len)
{
offset -= iov[which_iov].len;
++which_iov;
if (which_iov >= iovcnt)
break;
continue;
}
/*
* We want to avoid copying the data if at all possible, but every
* chunk of bytes we write into the queue has to be MAXALIGN'd, except
* the last. Thus, if a chunk other than the last one ends on a
* non-MAXALIGN'd boundary, we have to combine the tail end of its
* data with data from one or more following chunks until we either
* reach the last chunk or accumulate a number of bytes which is
* MAXALIGN'd.
*/
if (which_iov + 1 < iovcnt &&
offset + MAXIMUM_ALIGNOF > iov[which_iov].len)
{
char tmpbuf[MAXIMUM_ALIGNOF];
int j = 0;
for (;;)
{
if (offset < iov[which_iov].len)
{
tmpbuf[j] = iov[which_iov].data[offset];
j++;
offset++;
if (j == MAXIMUM_ALIGNOF)
break;
}
else
{
offset -= iov[which_iov].len;
which_iov++;
if (which_iov >= iovcnt)
break;
}
}
res = shm_mq_send_bytes(mqh, j, tmpbuf, nowait, &bytes_written);
mqh->mqh_partial_bytes += bytes_written;
if (res != SHM_MQ_SUCCESS)
return res;
continue;
}
/*
* If this is the last chunk, we can write all the data, even if it
* isn't a multiple of MAXIMUM_ALIGNOF. Otherwise, we need to
* MAXALIGN_DOWN the write size.
*/
chunksize = iov[which_iov].len - offset;
if (which_iov + 1 < iovcnt)
chunksize = MAXALIGN_DOWN(chunksize);
res = shm_mq_send_bytes(mqh, chunksize, &iov[which_iov].data[offset],
nowait, &bytes_written);
mqh->mqh_partial_bytes += bytes_written;
offset += bytes_written;
if (res != SHM_MQ_SUCCESS)
return res;
} while (mqh->mqh_partial_bytes < nbytes);
/* Reset for next message. */
mqh->mqh_partial_bytes = 0;
mqh->mqh_length_word_complete = false;
/* Notify receiver of the newly-written data, and return. */
return shm_mq_notify_receiver(mq);
}
