ipc.h

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/*-------------------------------------------------------------------------
 *
 * ipc.h
 *    POSTGRES inter-process communication definitions.
 *
 * This file is misnamed, as it no longer has much of anything directly
 * to do with IPC.  The functionality here is concerned with managing
 * exit-time cleanup for either a postmaster or a backend.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/ipc.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef IPC_H
#define IPC_H

typedef void (*pg_on_exit_callback) (int code, Datum arg);
typedef void (*shmem_startup_hook_type) (void);

/*----------
 * API for handling cleanup that must occur during either ereport(ERROR)
 * or ereport(FATAL) exits from a block of code.  (Typical examples are
 * undoing transient changes to shared-memory state.)
 *
 *      PG_ENSURE_ERROR_CLEANUP(cleanup_function, arg);
 *      {
 *          ... code that might throw ereport(ERROR) or ereport(FATAL) ...
 *      }
 *      PG_END_ENSURE_ERROR_CLEANUP(cleanup_function, arg);
 *
 * where the cleanup code is in a function declared per pg_on_exit_callback.
 * The Datum value "arg" can carry any information the cleanup function
 * needs.
 *
 * This construct ensures that cleanup_function() will be called during
 * either ERROR or FATAL exits.  It will not be called on successful
 * exit from the controlled code.  (If you want it to happen then too,
 * call the function yourself from just after the construct.)
 *
 * Note: the macro arguments are multiply evaluated, so avoid side-effects.
 *----------
 */
#define PG_ENSURE_ERROR_CLEANUP(cleanup_function, arg)  \
    do { \
        before_shmem_exit(cleanup_function, arg); \
        PG_TRY()

#define PG_END_ENSURE_ERROR_CLEANUP(cleanup_function, arg)  \
        cancel_before_shmem_exit(cleanup_function, arg); \
        PG_CATCH(); \
        { \
            cancel_before_shmem_exit(cleanup_function, arg); \
            cleanup_function (0, arg); \
            PG_RE_THROW(); \
        } \
        PG_END_TRY(); \
    } while (0)


/* ipc.c */
extern PGDLLIMPORT bool proc_exit_inprogress;
extern PGDLLIMPORT bool shmem_exit_inprogress;

extern void proc_exit(int code) pg_attribute_noreturn();
extern void shmem_exit(int code);
extern void on_proc_exit(pg_on_exit_callback function, Datum arg);
extern void on_shmem_exit(pg_on_exit_callback function, Datum arg);
extern void before_shmem_exit(pg_on_exit_callback function, Datum arg);
extern void cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg);
extern void on_exit_reset(void);

/* ipci.c */
extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;

extern void CreateSharedMemoryAndSemaphores(void);

#endif                          /* IPC_H */