1 /*--------------------------------------------------------------------
3 * POSTGRES pluggable background workers interface
5 * A background worker is a process able to run arbitrary, user-supplied code,
6 * including normal transactions.
8 * Any external module loaded via shared_preload_libraries can register a
9 * worker. Workers can also be registered dynamically at runtime. In either
10 * case, the worker process is forked from the postmaster and runs the
11 * user-supplied "main" function. This code may connect to a database and
12 * run transactions. Workers can remain active indefinitely, but will be
13 * terminated if a shutdown or crash occurs.
15 * If the fork() call fails in the postmaster, it will try again later. Note
16 * that the failure can only be transient (fork failure due to high load,
17 * memory pressure, too many processes, etc); more permanent problems, like
18 * failure to connect to a database, are detected later in the worker and dealt
19 * with just by having the worker exit normally. A worker which exits with
20 * a return code of 0 will never be restarted and will be removed from worker
21 * list. A worker which exits with a return code of 1 will be restarted after
22 * the configured restart interval (unless that interval is BGW_NEVER_RESTART).
23 * The TerminateBackgroundWorker() function can be used to terminate a
24 * dynamically registered background worker; the worker will be sent a SIGTERM
25 * and will not be restarted after it exits. Whenever the postmaster knows
26 * that a worker will not be restarted, it unregisters the worker, freeing up
27 * that worker's slot for use by a new worker.
29 * Note that there might be more than one worker in a database concurrently,
30 * and the same module may request more than one worker running the same (or
34 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
35 * Portions Copyright (c) 1994, Regents of the University of California
38 * src/include/postmaster/bgworker.h
39 *--------------------------------------------------------------------
44 /*---------------------------------------------------------------------
45 * External module API.
46 *---------------------------------------------------------------------
50 * Pass this flag to have your worker be able to connect to shared memory.
52 #define BGWORKER_SHMEM_ACCESS 0x0001
55 * This flag means the bgworker requires a database connection. The connection
56 * is not established automatically; the worker must establish it later.
57 * It requires that BGWORKER_SHMEM_ACCESS was passed too.
59 #define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
62 typedef void (*bgworker_main_type) (Datum main_arg);
65 * Points in time at which a bgworker can request to be started
69 BgWorkerStart_PostmasterStart,
70 BgWorkerStart_ConsistentState,
71 BgWorkerStart_RecoveryFinished
74 #define BGW_DEFAULT_RESTART_INTERVAL 60
75 #define BGW_NEVER_RESTART -1
78 typedef struct BackgroundWorker
80 char bgw_name[BGW_MAXLEN];
82 BgWorkerStartTime bgw_start_time;
83 int bgw_restart_time; /* in seconds, or BGW_NEVER_RESTART */
84 bgworker_main_type bgw_main;
85 char bgw_library_name[BGW_MAXLEN]; /* only if bgw_main is NULL */
86 char bgw_function_name[BGW_MAXLEN]; /* only if bgw_main is NULL */
88 pid_t bgw_notify_pid; /* SIGUSR1 this backend on start/stop */
91 typedef enum BgwHandleStatus
93 BGWH_STARTED, /* worker is running */
94 BGWH_NOT_YET_STARTED, /* worker hasn't been started yet */
95 BGWH_STOPPED, /* worker has exited */
96 BGWH_POSTMASTER_DIED /* postmaster died; worker status unclear */
99 struct BackgroundWorkerHandle;
100 typedef struct BackgroundWorkerHandle BackgroundWorkerHandle;
102 /* Register a new bgworker during shared_preload_libraries */
103 extern void RegisterBackgroundWorker(BackgroundWorker *worker);
105 /* Register a new bgworker from a regular backend */
106 extern bool RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
107 BackgroundWorkerHandle **handle);
109 /* Query the status of a bgworker */
110 extern BgwHandleStatus GetBackgroundWorkerPid(BackgroundWorkerHandle *handle,
112 extern BgwHandleStatus
113 WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *
116 /* Terminate a bgworker */
117 extern void TerminateBackgroundWorker(BackgroundWorkerHandle *handle);
119 /* This is valid in a running worker */
120 extern PGDLLIMPORT BackgroundWorker *MyBgworkerEntry;
123 * Connect to the specified database, as the specified user. Only a worker
124 * that passed BGWORKER_BACKEND_DATABASE_CONNECTION during registration may
127 * If username is NULL, bootstrapping superuser is used.
128 * If dbname is NULL, connection is made to no specific database;
129 * only shared catalogs can be accessed.
131 extern void BackgroundWorkerInitializeConnection(char *dbname, char *username);
133 /* Just like the above, but specifying database and user by OID. */
134 extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid);
136 /* Block/unblock signals in a background worker process */
137 extern void BackgroundWorkerBlockSignals(void);
138 extern void BackgroundWorkerUnblockSignals(void);
140 #endif /* BGWORKER_H */