1 /*-------------------------------------------------------------------------
4 * single-reader, single-writer shared memory message queue
6 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
9 * src/include/storage/shm_mq.h
11 *-------------------------------------------------------------------------
16 #include "postmaster/bgworker.h"
17 #include "storage/dsm.h"
18 #include "storage/proc.h"
20 /* The queue itself, in shared memory. */
22 typedef struct shm_mq shm_mq;
24 /* Backend-private state. */
26 typedef struct shm_mq_handle shm_mq_handle;
28 /* Descriptors for a single write spanning multiple locations. */
35 /* Possible results of a send or receive operation. */
38 SHM_MQ_SUCCESS, /* Sent or received a message. */
39 SHM_MQ_WOULD_BLOCK, /* Not completed; retry later. */
40 SHM_MQ_DETACHED /* Other process has detached queue. */
44 * Primitives to create a queue and set the sender and receiver.
46 * Both the sender and the receiver must be set before any messages are read
47 * or written, but they need not be set by the same process. Each must be
50 extern shm_mq *shm_mq_create(void *address, Size size);
51 extern void shm_mq_set_receiver(shm_mq *mq, PGPROC *);
52 extern void shm_mq_set_sender(shm_mq *mq, PGPROC *);
54 /* Accessor methods for sender and receiver. */
55 extern PGPROC *shm_mq_get_receiver(shm_mq *);
56 extern PGPROC *shm_mq_get_sender(shm_mq *);
58 /* Set up backend-local queue state. */
59 extern shm_mq_handle *shm_mq_attach(shm_mq *mq, dsm_segment *seg,
60 BackgroundWorkerHandle *handle);
62 /* Associate worker handle with shm_mq. */
63 extern void shm_mq_set_handle(shm_mq_handle *, BackgroundWorkerHandle *);
65 /* Break connection. */
66 extern void shm_mq_detach(shm_mq *);
68 /* Send or receive messages. */
69 extern shm_mq_result shm_mq_send(shm_mq_handle *mqh,
70 Size nbytes, const void *data, bool nowait);
71 extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh,
72 shm_mq_iovec *iov, int iovcnt, bool nowait);
73 extern shm_mq_result shm_mq_receive(shm_mq_handle *mqh,
74 Size *nbytesp, void **datap, bool nowait);
76 /* Wait for our counterparty to attach to the queue. */
77 extern shm_mq_result shm_mq_wait_for_attach(shm_mq_handle *mqh);
79 /* Smallest possible queue. */
80 extern PGDLLIMPORT const Size shm_mq_minimum_size;