shm_mq.h File Reference

#include "postmaster/bgworker.h"
#include "storage/dsm.h"
#include "storage/proc.h"

Include dependency graph for shm_mq.h:

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Go to the source code of this file.

Data Structures
struct	shm_mq_iovec

Typedefs
typedef struct shm_mq	shm_mq
typedef struct shm_mq_handle	shm_mq_handle

Enumerations
enum	shm_mq_result { SHM_MQ_SUCCESS, SHM_MQ_WOULD_BLOCK, SHM_MQ_DETACHED }

Functions
shm_mq *	shm_mq_create (void *address, Size size)
void	shm_mq_set_receiver (shm_mq *mq, PGPROC *)
void	shm_mq_set_sender (shm_mq *mq, PGPROC *)
PGPROC *	shm_mq_get_receiver (shm_mq *)
PGPROC *	shm_mq_get_sender (shm_mq *)
shm_mq_handle *	shm_mq_attach (shm_mq *mq, dsm_segment *seg, BackgroundWorkerHandle *handle)
void	shm_mq_set_handle (shm_mq_handle *, BackgroundWorkerHandle *)
void	shm_mq_detach (shm_mq_handle *mqh)
shm_mq *	shm_mq_get_queue (shm_mq_handle *mqh)
shm_mq_result	shm_mq_send (shm_mq_handle *mqh, Size nbytes, const void *data, bool nowait)
shm_mq_result	shm_mq_sendv (shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait)
shm_mq_result	shm_mq_receive (shm_mq_handle *mqh, Size *nbytesp, void **datap, bool nowait)
shm_mq_result	shm_mq_wait_for_attach (shm_mq_handle *mqh)

Variables
PGDLLIMPORT const Size	shm_mq_minimum_size

Typedef Documentation

shm_mq

typedef struct shm_mq shm_mq

Definition at line 22 of file shm_mq.h.

shm_mq_handle

typedef struct shm_mq_handle shm_mq_handle

Definition at line 26 of file shm_mq.h.

Enumeration Type Documentation

shm_mq_result

enum shm_mq_result

Enumerator
SHM_MQ_SUCCESS
SHM_MQ_WOULD_BLOCK
SHM_MQ_DETACHED

Definition at line 36 of file shm_mq.h.

{
    SHM_MQ_SUCCESS,             /* Sent or received a message. */
    SHM_MQ_WOULD_BLOCK,         /* Not completed; retry later. */
    SHM_MQ_DETACHED             /* Other process has detached queue. */
} shm_mq_result;

Function Documentation

shm_mq_attach()

shm_mq_handle* shm_mq_attach	(	shm_mq *	mq,
		dsm_segment *	seg,
		BackgroundWorkerHandle *	handle
	)

Definition at line 283 of file shm_mq.c.

References Assert, CurrentMemoryContext, shm_mq::mq_receiver, shm_mq::mq_sender, shm_mq_handle::mqh_buffer, shm_mq_handle::mqh_buflen, shm_mq_handle::mqh_consume_pending, shm_mq_handle::mqh_context, shm_mq_handle::mqh_counterparty_attached, shm_mq_handle::mqh_expected_bytes, shm_mq_handle::mqh_handle, shm_mq_handle::mqh_length_word_complete, shm_mq_handle::mqh_partial_bytes, shm_mq_handle::mqh_queue, shm_mq_handle::mqh_segment, MyProc, on_dsm_detach(), palloc(), PointerGetDatum, and shm_mq_detach_callback().

Referenced by attach_to_queues(), ExecParallelGetReceiver(), ExecParallelSetupTupleQueues(), InitializeParallelDSM(), ParallelWorkerMain(), ReinitializeParallelDSM(), and test_shm_mq_setup().

{
    shm_mq_handle *mqh = palloc(sizeof(shm_mq_handle));

    Assert(mq->mq_receiver == MyProc || mq->mq_sender == MyProc);
    mqh->mqh_queue = mq;
    mqh->mqh_segment = seg;
    mqh->mqh_handle = handle;
    mqh->mqh_buffer = NULL;
    mqh->mqh_buflen = 0;
    mqh->mqh_consume_pending = 0;
    mqh->mqh_partial_bytes = 0;
    mqh->mqh_expected_bytes = 0;
    mqh->mqh_length_word_complete = false;
    mqh->mqh_counterparty_attached = false;
    mqh->mqh_context = CurrentMemoryContext;

    if (seg != NULL)
        on_dsm_detach(seg, shm_mq_detach_callback, PointerGetDatum(mq));

    return mqh;
}

shm_mq_create()

shm_mq* shm_mq_create	(	void *	address,
		Size	size
	)

Definition at line 170 of file shm_mq.c.

References Assert, MAXALIGN, MAXALIGN_DOWN, shm_mq::mq_bytes_read, shm_mq::mq_bytes_written, shm_mq::mq_detached, shm_mq::mq_mutex, shm_mq::mq_receiver, shm_mq::mq_ring, shm_mq::mq_ring_offset, shm_mq::mq_ring_size, shm_mq::mq_sender, offsetof, pg_atomic_init_u64(), and SpinLockInit.

Referenced by ExecParallelSetupTupleQueues(), InitializeParallelDSM(), ReinitializeParallelDSM(), and setup_dynamic_shared_memory().

{
    shm_mq     *mq = address;
    Size        data_offset = MAXALIGN(offsetof(shm_mq, mq_ring));

    /* If the size isn't MAXALIGN'd, just discard the odd bytes. */
    size = MAXALIGN_DOWN(size);

    /* Queue size must be large enough to hold some data. */
    Assert(size > data_offset);

    /* Initialize queue header. */
    SpinLockInit(&mq->mq_mutex);
    mq->mq_receiver = NULL;
    mq->mq_sender = NULL;
    pg_atomic_init_u64(&mq->mq_bytes_read, 0);
    pg_atomic_init_u64(&mq->mq_bytes_written, 0);
    mq->mq_ring_size = size - data_offset;
    mq->mq_detached = false;
    mq->mq_ring_offset = data_offset - offsetof(shm_mq, mq_ring);

    return mq;
}

shm_mq_detach()

void shm_mq_detach

(

shm_mq_handle *

mqh

)

Definition at line 817 of file shm_mq.c.

References cancel_on_dsm_detach(), shm_mq_handle::mqh_buffer, shm_mq_handle::mqh_queue, shm_mq_handle::mqh_segment, pfree(), PointerGetDatum, shm_mq_detach_callback(), and shm_mq_detach_internal().

Referenced by DestroyParallelContext(), ExecParallelFinish(), HandleParallelMessage(), LaunchParallelWorkers(), mq_putmessage(), tqueueDestroyReceiver(), and tqueueShutdownReceiver().

{
    /* Notify counterparty that we're outta here. */
    shm_mq_detach_internal(mqh->mqh_queue);

    /* Cancel on_dsm_detach callback, if any. */
    if (mqh->mqh_segment)
        cancel_on_dsm_detach(mqh->mqh_segment,
                             shm_mq_detach_callback,
                             PointerGetDatum(mqh->mqh_queue));

    /* Release local memory associated with handle. */
    if (mqh->mqh_buffer != NULL)
        pfree(mqh->mqh_buffer);
    pfree(mqh);
}

shm_mq_get_queue()

shm_mq* shm_mq_get_queue

(

shm_mq_handle *

mqh

)

Definition at line 872 of file shm_mq.c.

References shm_mq_handle::mqh_queue.

Referenced by WaitForParallelWorkersToAttach(), and WaitForParallelWorkersToFinish().

{
    return mqh->mqh_queue;
}

shm_mq_get_receiver()

PGPROC* shm_mq_get_receiver

(

shm_mq *

)

Definition at line 235 of file shm_mq.c.

References shm_mq::mq_mutex, shm_mq::mq_receiver, SpinLockAcquire, and SpinLockRelease.

Referenced by shm_mq_send_bytes(), and shm_mq_wait_for_attach().

{
    PGPROC     *receiver;

    SpinLockAcquire(&mq->mq_mutex);
    receiver = mq->mq_receiver;
    SpinLockRelease(&mq->mq_mutex);

    return receiver;
}

shm_mq_get_sender()

PGPROC* shm_mq_get_sender

(

shm_mq *

)

Definition at line 250 of file shm_mq.c.

References shm_mq::mq_mutex, shm_mq::mq_sender, SpinLockAcquire, and SpinLockRelease.

Referenced by shm_mq_receive(), shm_mq_wait_for_attach(), WaitForParallelWorkersToAttach(), and WaitForParallelWorkersToFinish().

{
    PGPROC     *sender;

    SpinLockAcquire(&mq->mq_mutex);
    sender = mq->mq_sender;
    SpinLockRelease(&mq->mq_mutex);

    return sender;
}

shm_mq_receive()

shm_mq_result shm_mq_receive	(	shm_mq_handle *	mqh,
		Size *	nbytesp,
		void **	datap,
		bool	nowait
	)

Definition at line 548 of file shm_mq.c.

References Assert, ereport, errcode(), errmsg(), ERROR, Max, MAXALIGN, MaxAllocSize, MemoryContextAlloc(), Min, shm_mq::mq_detached, shm_mq::mq_receiver, shm_mq::mq_ring_size, shm_mq::mq_sender, shm_mq_handle::mqh_buffer, shm_mq_handle::mqh_buflen, shm_mq_handle::mqh_consume_pending, shm_mq_handle::mqh_context, shm_mq_handle::mqh_counterparty_attached, shm_mq_handle::mqh_expected_bytes, shm_mq_handle::mqh_handle, MQH_INITIAL_BUFSIZE, shm_mq_handle::mqh_length_word_complete, shm_mq_handle::mqh_partial_bytes, shm_mq_handle::mqh_queue, MyProc, pfree(), shm_mq_counterparty_gone(), SHM_MQ_DETACHED, shm_mq_get_sender(), shm_mq_inc_bytes_read(), shm_mq_receive_bytes(), SHM_MQ_SUCCESS, shm_mq_wait_internal(), and SHM_MQ_WOULD_BLOCK.

Referenced by copy_messages(), HandleParallelMessages(), test_shm_mq(), test_shm_mq_pipelined(), and TupleQueueReaderNext().

{
    shm_mq     *mq = mqh->mqh_queue;
    shm_mq_result res;
    Size        rb = 0;
    Size        nbytes;
    void       *rawdata;

    Assert(mq->mq_receiver == MyProc);

    /* We can't receive data until the sender has attached. */
    if (!mqh->mqh_counterparty_attached)
    {
        if (nowait)
        {
            int         counterparty_gone;

            /*
             * We shouldn't return at this point at all unless the sender
             * hasn't attached yet.  However, the correct return value depends
             * on whether the sender is still attached.  If we first test
             * whether the sender has ever attached and then test whether the
             * sender has detached, there's a race condition: a sender that
             * attaches and detaches very quickly might fool us into thinking
             * the sender never attached at all.  So, test whether our
             * counterparty is definitively gone first, and only afterwards
             * check whether the sender ever attached in the first place.
             */
            counterparty_gone = shm_mq_counterparty_gone(mq, mqh->mqh_handle);
            if (shm_mq_get_sender(mq) == NULL)
            {
                if (counterparty_gone)
                    return SHM_MQ_DETACHED;
                else
                    return SHM_MQ_WOULD_BLOCK;
            }
        }
        else if (!shm_mq_wait_internal(mq, &mq->mq_sender, mqh->mqh_handle)
                 && shm_mq_get_sender(mq) == NULL)
        {
            mq->mq_detached = true;
            return SHM_MQ_DETACHED;
        }
        mqh->mqh_counterparty_attached = true;
    }

    /*
     * If we've consumed an amount of data greater than 1/4th of the ring
     * size, mark it consumed in shared memory.  We try to avoid doing this
     * unnecessarily when only a small amount of data has been consumed,
     * because SetLatch() is fairly expensive and we don't want to do it too
     * often.
     */
    if (mqh->mqh_consume_pending > mq->mq_ring_size / 4)
    {
        shm_mq_inc_bytes_read(mq, mqh->mqh_consume_pending);
        mqh->mqh_consume_pending = 0;
    }

    /* Try to read, or finish reading, the length word from the buffer. */
    while (!mqh->mqh_length_word_complete)
    {
        /* Try to receive the message length word. */
        Assert(mqh->mqh_partial_bytes < sizeof(Size));
        res = shm_mq_receive_bytes(mqh, sizeof(Size) - mqh->mqh_partial_bytes,
                                   nowait, &rb, &rawdata);
        if (res != SHM_MQ_SUCCESS)
            return res;

        /*
         * Hopefully, we'll receive the entire message length word at once.
         * But if sizeof(Size) > MAXIMUM_ALIGNOF, then it might be split over
         * multiple reads.
         */
        if (mqh->mqh_partial_bytes == 0 && rb >= sizeof(Size))
        {
            Size        needed;

            nbytes = *(Size *) rawdata;

            /* If we've already got the whole message, we're done. */
            needed = MAXALIGN(sizeof(Size)) + MAXALIGN(nbytes);
            if (rb >= needed)
            {
                mqh->mqh_consume_pending += needed;
                *nbytesp = nbytes;
                *datap = ((char *) rawdata) + MAXALIGN(sizeof(Size));
                return SHM_MQ_SUCCESS;
            }

            /*
             * We don't have the whole message, but we at least have the whole
             * length word.
             */
            mqh->mqh_expected_bytes = nbytes;
            mqh->mqh_length_word_complete = true;
            mqh->mqh_consume_pending += MAXALIGN(sizeof(Size));
            rb -= MAXALIGN(sizeof(Size));
        }
        else
        {
            Size        lengthbytes;

            /* Can't be split unless bigger than required alignment. */
            Assert(sizeof(Size) > MAXIMUM_ALIGNOF);

            /* Message word is split; need buffer to reassemble. */
            if (mqh->mqh_buffer == NULL)
            {
                mqh->mqh_buffer = MemoryContextAlloc(mqh->mqh_context,
                                                     MQH_INITIAL_BUFSIZE);
                mqh->mqh_buflen = MQH_INITIAL_BUFSIZE;
            }
            Assert(mqh->mqh_buflen >= sizeof(Size));

            /* Copy partial length word; remember to consume it. */
            if (mqh->mqh_partial_bytes + rb > sizeof(Size))
                lengthbytes = sizeof(Size) - mqh->mqh_partial_bytes;
            else
                lengthbytes = rb;
            memcpy(&mqh->mqh_buffer[mqh->mqh_partial_bytes], rawdata,
                   lengthbytes);
            mqh->mqh_partial_bytes += lengthbytes;
            mqh->mqh_consume_pending += MAXALIGN(lengthbytes);
            rb -= lengthbytes;

            /* If we now have the whole word, we're ready to read payload. */
            if (mqh->mqh_partial_bytes >= sizeof(Size))
            {
                Assert(mqh->mqh_partial_bytes == sizeof(Size));
                mqh->mqh_expected_bytes = *(Size *) mqh->mqh_buffer;
                mqh->mqh_length_word_complete = true;
                mqh->mqh_partial_bytes = 0;
            }
        }
    }
    nbytes = mqh->mqh_expected_bytes;

    /*
     * Should be disallowed on the sending side already, but better check and
     * error out on the receiver side as well rather than trying to read a
     * prohibitively large message.
     */
    if (nbytes > MaxAllocSize)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("invalid message size %zu in shared memory queue",
                        nbytes)));

    if (mqh->mqh_partial_bytes == 0)
    {
        /*
         * Try to obtain the whole message in a single chunk.  If this works,
         * we need not copy the data and can return a pointer directly into
         * shared memory.
         */
        res = shm_mq_receive_bytes(mqh, nbytes, nowait, &rb, &rawdata);
        if (res != SHM_MQ_SUCCESS)
            return res;
        if (rb >= nbytes)
        {
            mqh->mqh_length_word_complete = false;
            mqh->mqh_consume_pending += MAXALIGN(nbytes);
            *nbytesp = nbytes;
            *datap = rawdata;
            return SHM_MQ_SUCCESS;
        }

        /*
         * The message has wrapped the buffer.  We'll need to copy it in order
         * to return it to the client in one chunk.  First, make sure we have
         * a large enough buffer available.
         */
        if (mqh->mqh_buflen < nbytes)
        {
            Size        newbuflen = Max(mqh->mqh_buflen, MQH_INITIAL_BUFSIZE);

            /*
             * Double the buffer size until the payload fits, but limit to
             * MaxAllocSize.
             */
            while (newbuflen < nbytes)
                newbuflen *= 2;
            newbuflen = Min(newbuflen, MaxAllocSize);

            if (mqh->mqh_buffer != NULL)
            {
                pfree(mqh->mqh_buffer);
                mqh->mqh_buffer = NULL;
                mqh->mqh_buflen = 0;
            }
            mqh->mqh_buffer = MemoryContextAlloc(mqh->mqh_context, newbuflen);
            mqh->mqh_buflen = newbuflen;
        }
    }

    /* Loop until we've copied the entire message. */
    for (;;)
    {
        Size        still_needed;

        /* Copy as much as we can. */
        Assert(mqh->mqh_partial_bytes + rb <= nbytes);
        memcpy(&mqh->mqh_buffer[mqh->mqh_partial_bytes], rawdata, rb);
        mqh->mqh_partial_bytes += rb;

        /*
         * Update count of bytes that can be consumed, accounting for
         * alignment padding.  Note that this will never actually insert any
         * padding except at the end of a message, because the buffer size is
         * a multiple of MAXIMUM_ALIGNOF, and each read and write is as well.
         */
        Assert(mqh->mqh_partial_bytes == nbytes || rb == MAXALIGN(rb));
        mqh->mqh_consume_pending += MAXALIGN(rb);

        /* If we got all the data, exit the loop. */
        if (mqh->mqh_partial_bytes >= nbytes)
            break;

        /* Wait for some more data. */
        still_needed = nbytes - mqh->mqh_partial_bytes;
        res = shm_mq_receive_bytes(mqh, still_needed, nowait, &rb, &rawdata);
        if (res != SHM_MQ_SUCCESS)
            return res;
        if (rb > still_needed)
            rb = still_needed;
    }

    /* Return the complete message, and reset for next message. */
    *nbytesp = nbytes;
    *datap = mqh->mqh_buffer;
    mqh->mqh_length_word_complete = false;
    mqh->mqh_partial_bytes = 0;
    return SHM_MQ_SUCCESS;
}

shm_mq_send()

shm_mq_result shm_mq_send	(	shm_mq_handle *	mqh,
		Size	nbytes,
		const void *	data,
		bool	nowait
	)

Definition at line 321 of file shm_mq.c.

References shm_mq_iovec::data, shm_mq_iovec::len, and shm_mq_sendv().

Referenced by copy_messages(), test_shm_mq(), test_shm_mq_pipelined(), and tqueueReceiveSlot().

{
    shm_mq_iovec iov;

    iov.data = data;
    iov.len = nbytes;

    return shm_mq_sendv(mqh, &iov, 1, nowait);
}

shm_mq_sendv()

shm_mq_result shm_mq_sendv	(	shm_mq_handle *	mqh,
		shm_mq_iovec *	iov,
		int	iovcnt,
		bool	nowait
	)

Definition at line 347 of file shm_mq.c.

References Assert, shm_mq_iovec::data, ereport, errcode(), errmsg(), ERROR, i, shm_mq_iovec::len, MAXALIGN_DOWN, MaxAllocSize, shm_mq::mq_detached, shm_mq::mq_mutex, shm_mq::mq_receiver, shm_mq::mq_sender, shm_mq_handle::mqh_counterparty_attached, shm_mq_handle::mqh_length_word_complete, shm_mq_handle::mqh_partial_bytes, shm_mq_handle::mqh_queue, MyProc, PGPROC::procLatch, SetLatch(), SHM_MQ_DETACHED, shm_mq_send_bytes(), SHM_MQ_SUCCESS, SpinLockAcquire, SpinLockRelease, and tmpbuf.

Referenced by mq_putmessage(), and shm_mq_send().

{
    shm_mq_result res;
    shm_mq     *mq = mqh->mqh_queue;
    PGPROC     *receiver;
    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;

    /* Prevent writing messages overwhelming the receiver. */
    if (nbytes > MaxAllocSize)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("cannot send a message of size %zu via shared memory queue",
                        nbytes)));

    /* 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);

        if (res == SHM_MQ_DETACHED)
        {
            /* Reset state in case caller tries to send another message. */
            mqh->mqh_partial_bytes = 0;
            mqh->mqh_length_word_complete = false;
            return res;
        }
        mqh->mqh_partial_bytes += bytes_written;

        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;
        }

        if (res != SHM_MQ_SUCCESS)
            return res;

        /* 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);

            if (res == SHM_MQ_DETACHED)
            {
                /* Reset state in case caller tries to send another message. */
                mqh->mqh_partial_bytes = 0;
                mqh->mqh_length_word_complete = false;
                return res;
            }

            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);

        if (res == SHM_MQ_DETACHED)
        {
            /* Reset state in case caller tries to send another message. */
            mqh->mqh_length_word_complete = false;
            mqh->mqh_partial_bytes = 0;
            return res;
        }

        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;

    /* If queue has been detached, let caller know. */
    if (mq->mq_detached)
        return SHM_MQ_DETACHED;

    /*
     * If the counterparty is known to have attached, we can read mq_receiver
     * without acquiring the spinlock and assume it isn't NULL.  Otherwise,
     * more caution is needed.
     */
    if (mqh->mqh_counterparty_attached)
        receiver = mq->mq_receiver;
    else
    {
        SpinLockAcquire(&mq->mq_mutex);
        receiver = mq->mq_receiver;
        SpinLockRelease(&mq->mq_mutex);
        if (receiver == NULL)
            return SHM_MQ_SUCCESS;
        mqh->mqh_counterparty_attached = true;
    }

    /* Notify receiver of the newly-written data, and return. */
    SetLatch(&receiver->procLatch);
    return SHM_MQ_SUCCESS;
}

shm_mq_set_handle()

void shm_mq_set_handle	(	shm_mq_handle *	,
		BackgroundWorkerHandle *
	)

Definition at line 311 of file shm_mq.c.

References Assert, and shm_mq_handle::mqh_handle.

Referenced by ExecParallelCreateReaders(), and LaunchParallelWorkers().

{
    Assert(mqh->mqh_handle == NULL);
    mqh->mqh_handle = handle;
}

shm_mq_set_receiver()

void shm_mq_set_receiver	(	shm_mq *	mq,
		PGPROC *
	)

Definition at line 199 of file shm_mq.c.

References Assert, shm_mq::mq_mutex, shm_mq::mq_receiver, shm_mq::mq_sender, PGPROC::procLatch, SetLatch(), SpinLockAcquire, and SpinLockRelease.

Referenced by attach_to_queues(), ExecParallelSetupTupleQueues(), InitializeParallelDSM(), ReinitializeParallelDSM(), and setup_dynamic_shared_memory().

{
    PGPROC     *sender;

    SpinLockAcquire(&mq->mq_mutex);
    Assert(mq->mq_receiver == NULL);
    mq->mq_receiver = proc;
    sender = mq->mq_sender;
    SpinLockRelease(&mq->mq_mutex);

    if (sender != NULL)
        SetLatch(&sender->procLatch);
}

shm_mq_set_sender()

void shm_mq_set_sender	(	shm_mq *	mq,
		PGPROC *
	)

Definition at line 217 of file shm_mq.c.

References Assert, shm_mq::mq_mutex, shm_mq::mq_receiver, shm_mq::mq_sender, PGPROC::procLatch, SetLatch(), SpinLockAcquire, and SpinLockRelease.

Referenced by attach_to_queues(), ExecParallelGetReceiver(), ParallelWorkerMain(), and setup_dynamic_shared_memory().

{
    PGPROC     *receiver;

    SpinLockAcquire(&mq->mq_mutex);
    Assert(mq->mq_sender == NULL);
    mq->mq_sender = proc;
    receiver = mq->mq_receiver;
    SpinLockRelease(&mq->mq_mutex);

    if (receiver != NULL)
        SetLatch(&receiver->procLatch);
}

shm_mq_wait_for_attach()

shm_mq_result shm_mq_wait_for_attach

(

shm_mq_handle *

mqh

)

Definition at line 794 of file shm_mq.c.

References Assert, shm_mq::mq_receiver, shm_mq::mq_sender, shm_mq_handle::mqh_handle, shm_mq_handle::mqh_queue, MyProc, SHM_MQ_DETACHED, shm_mq_get_receiver(), shm_mq_get_sender(), SHM_MQ_SUCCESS, and shm_mq_wait_internal().

{
    shm_mq     *mq = mqh->mqh_queue;
    PGPROC    **victim;

    if (shm_mq_get_receiver(mq) == MyProc)
        victim = &mq->mq_sender;
    else
    {
        Assert(shm_mq_get_sender(mq) == MyProc);
        victim = &mq->mq_receiver;
    }

    if (shm_mq_wait_internal(mq, victim, mqh->mqh_handle))
        return SHM_MQ_SUCCESS;
    else
        return SHM_MQ_DETACHED;
}

Variable Documentation

shm_mq_minimum_size

PGDLLIMPORT const Size shm_mq_minimum_size

Definition at line 161 of file shm_mq.c.

Referenced by setup_dynamic_shared_memory().