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/*--------------------------------------------------------------------
* bgworker.h
* POSTGRES pluggable background workers interface
*
* A background worker is a process able to run arbitrary, user-supplied code,
* including normal transactions.
*
* Any external module loaded via shared_preload_libraries can register a
* worker. Then, at the appropriate time, the worker process is forked from
* the postmaster and runs the user-supplied "main" function. This code may
* connect to a database and run transactions. Once started, it stays active
* until shutdown or crash. The process should sleep during periods of
* inactivity.
*
* If the fork() call fails in the postmaster, it will try again later. Note
* that the failure can only be transient (fork failure due to high load,
* memory pressure, too many processes, etc); more permanent problems, like
* failure to connect to a database, are detected later in the worker and dealt
* with just by having the worker exit normally. Postmaster will launch a new
* worker again later.
*
* Note that there might be more than one worker in a database concurrently,
* and the same module may request more than one worker running the same (or
* different) code.
*
*
* Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/include/postmaster/bgworker.h
*--------------------------------------------------------------------
*/
#ifndef BGWORKER_H
#define BGWORKER_H
/*---------------------------------------------------------------------
* External module API.
*---------------------------------------------------------------------
*/
/*
* Pass this flag to have your worker be able to connect to shared memory.
*/
#define BGWORKER_SHMEM_ACCESS 0x0001
/*
* This flag means the bgworker requires a database connection. The connection
* is not established automatically; the worker must establish it later.
* It requires that BGWORKER_SHMEM_ACCESS was passed too.
*/
#define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
typedef void (*bgworker_main_type)(void *main_arg);
typedef void (*bgworker_sighdlr_type)(SIGNAL_ARGS);
/*
* Points in time at which a bgworker can request to be started
*/
typedef enum
{
BgWorkerStart_PostmasterStart,
BgWorkerStart_ConsistentState,
BgWorkerStart_RecoveryFinished
} BgWorkerStartTime;
#define BGW_DEFAULT_RESTART_INTERVAL 60
#define BGW_NEVER_RESTART -1
typedef struct BackgroundWorker
{
char *bgw_name;
int bgw_flags;
BgWorkerStartTime bgw_start_time;
int bgw_restart_time; /* in seconds, or BGW_NEVER_RESTART */
bgworker_main_type bgw_main;
void *bgw_main_arg;
bgworker_sighdlr_type bgw_sighup;
bgworker_sighdlr_type bgw_sigterm;
} BackgroundWorker;
/* Register a new bgworker */
extern void RegisterBackgroundWorker(BackgroundWorker *worker);
/* This is valid in a running worker */
extern BackgroundWorker *MyBgworkerEntry;
/*
* Connect to the specified database, as the specified user. Only a worker
* that passed BGWORKER_BACKEND_DATABASE_CONNECTION during registration may
* call this.
*
* If username is NULL, bootstrapping superuser is used.
* If dbname is NULL, connection is made to no specific database;
* only shared catalogs can be accessed.
*/
extern void BackgroundWorkerInitializeConnection(char *dbname, char *username);
/* Block/unblock signals in a background worker process */
extern void BackgroundWorkerBlockSignals(void);
extern void BackgroundWorkerUnblockSignals(void);
#endif /* BGWORKER_H */
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