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/*------------------------------------------------------------------------- * * shm_mq.h * single-reader, single-writer shared memory message queue * * Portions Copyright (c) 1996-2016, 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. */ extern void shm_mq_detach(shm_mq *); /* 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); extern shm_mq_result shm_mq_sendv(shm_mq_handle *mqh, shm_mq_iovec *iov, int iovcnt, bool nowait); 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 */