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/*-------------------------------------------------------------------------
*
* shm_mq.h
* single-reader, single-writer shared memory message queue
*
* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/shm_mq.h
*
*-------------------------------------------------------------------------
*/
#ifndef SHM_MQ_H
#define SHM_MQ_H
#include "postmaster/bgworker.h"
#include "storage/dsm.h"
#include "storage/proc.h"
/* The queue itself, in shared memory. */
struct shm_mq;
typedef struct shm_mq shm_mq;
/* Backend-private state. */
struct shm_mq_handle;
typedef struct shm_mq_handle shm_mq_handle;
/* Descriptors for a single write spanning multiple locations. */
typedef struct
{
const char *data;
Size len;
} shm_mq_iovec;
/* Possible results of a send or receive operation. */
typedef enum
{
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;
/*
* Primitives to create a queue and set the sender and receiver.
*
* Both the sender and the receiver must be set before any messages are read
* or written, but they need not be set by the same process. Each must be
* set exactly once.
*/
extern shm_mq *shm_mq_create(void *address, Size size);
extern void shm_mq_set_receiver(shm_mq *mq, PGPROC *);
extern void shm_mq_set_sender(shm_mq *mq, PGPROC *);
/* Accessor methods for sender and receiver. */
extern PGPROC *shm_mq_get_receiver(shm_mq *);
extern PGPROC *shm_mq_get_sender(shm_mq *);
/* Set up backend-local queue state. */
extern shm_mq_handle *shm_mq_attach(shm_mq *mq, dsm_segment *seg,
BackgroundWorkerHandle *handle);
/* Associate worker handle with shm_mq. */
extern void shm_mq_set_handle(shm_mq_handle *, BackgroundWorkerHandle *);
/* Break connection, release handle resources. */
extern void shm_mq_detach(shm_mq_handle *mqh);
/* Get the shm_mq from handle. */
extern shm_mq *shm_mq_get_queue(shm_mq_handle *mqh);
/* Send or receive messages. */
extern shm_mq_result shm_mq_send(shm_mq_handle *mqh,
Size nbytes, const void *data, bool nowait,
bool force_flush);
extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov,
int iovcnt, bool nowait, bool force_flush);
extern shm_mq_result shm_mq_receive(shm_mq_handle *mqh,
Size *nbytesp, void **datap, bool nowait);
/* Wait for our counterparty to attach to the queue. */
extern shm_mq_result shm_mq_wait_for_attach(shm_mq_handle *mqh);
/* Smallest possible queue. */
extern PGDLLIMPORT const Size shm_mq_minimum_size;
#endif /* SHM_MQ_H */
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