1/*--------------------------------------------------------------------
2 * bgworker.h
3 * POSTGRES pluggable background workers interface
4 *
5 * A background worker is a process able to run arbitrary, user-supplied code,
6 * including normal transactions.
7 *
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.
14 *
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.
28 *
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
31 * different) code.
32 *
33 *
34 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
35 * Portions Copyright (c) 1994, Regents of the University of California
36 *
37 * IDENTIFICATION
38 * src/include/postmaster/bgworker.h
39 *--------------------------------------------------------------------
40 */
41#ifndef BGWORKER_H
42#define BGWORKER_H
43
44/*---------------------------------------------------------------------
45 * External module API.
46 *---------------------------------------------------------------------
47 */
48
49/*
50 * Pass this flag to have your worker be able to connect to shared memory.
51 */
52#define BGWORKER_SHMEM_ACCESS 0x0001
53
54/*
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.
58 */
59#define BGWORKER_BACKEND_DATABASE_CONNECTION 0x0002
60
61/*
62 * This class is used internally for parallel queries, to keep track of the
63 * number of active parallel workers and make sure we never launch more than
64 * max_parallel_workers parallel workers at the same time. Third party
65 * background workers should not use this class.
66 */
67#define BGWORKER_CLASS_PARALLEL 0x0010
68/* add additional bgworker classes here */
69
70
71typedef void (*bgworker_main_type) (Datum main_arg);
72
73/*
74 * Points in time at which a bgworker can request to be started
75 */
76typedef enum
77{
78 BgWorkerStart_PostmasterStart,
79 BgWorkerStart_ConsistentState,
80 BgWorkerStart_RecoveryFinished
81} BgWorkerStartTime;
82
83#define BGW_DEFAULT_RESTART_INTERVAL 60
84#define BGW_NEVER_RESTART -1
85#define BGW_MAXLEN 96
86#define BGW_EXTRALEN 128
87
88typedef struct BackgroundWorker
89{
90 char bgw_name[BGW_MAXLEN];
91 char bgw_type[BGW_MAXLEN];
92 int bgw_flags;
93 BgWorkerStartTime bgw_start_time;
94 int bgw_restart_time; /* in seconds, or BGW_NEVER_RESTART */
95 char bgw_library_name[BGW_MAXLEN];
96 char bgw_function_name[BGW_MAXLEN];
97 Datum bgw_main_arg;
98 char bgw_extra[BGW_EXTRALEN];
99 pid_t bgw_notify_pid; /* SIGUSR1 this backend on start/stop */
100} BackgroundWorker;
101
102typedef enum BgwHandleStatus
103{
104 BGWH_STARTED, /* worker is running */
105 BGWH_NOT_YET_STARTED, /* worker hasn't been started yet */
106 BGWH_STOPPED, /* worker has exited */
107 BGWH_POSTMASTER_DIED /* postmaster died; worker status unclear */
108} BgwHandleStatus;
109
110struct BackgroundWorkerHandle;
111typedef struct BackgroundWorkerHandle BackgroundWorkerHandle;
112
113/* Register a new bgworker during shared_preload_libraries */
114extern void RegisterBackgroundWorker(BackgroundWorker *worker);
115
116/* Register a new bgworker from a regular backend */
117extern bool RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
118 BackgroundWorkerHandle **handle);
119
120/* Query the status of a bgworker */
121extern BgwHandleStatus GetBackgroundWorkerPid(BackgroundWorkerHandle *handle,
122 pid_t *pidp);
123extern BgwHandleStatus WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pid);
124extern BgwHandleStatus
125 WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *);
126extern const char *GetBackgroundWorkerTypeByPid(pid_t pid);
127
128/* Terminate a bgworker */
129extern void TerminateBackgroundWorker(BackgroundWorkerHandle *handle);
130
131/* This is valid in a running worker */
132extern PGDLLIMPORT BackgroundWorker *MyBgworkerEntry;
133
134/*
135 * Connect to the specified database, as the specified user. Only a worker
136 * that passed BGWORKER_BACKEND_DATABASE_CONNECTION during registration may
137 * call this.
138 *
139 * If username is NULL, bootstrapping superuser is used.
140 * If dbname is NULL, connection is made to no specific database;
141 * only shared catalogs can be accessed.
142 */
143extern void BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags);
144
145/* Just like the above, but specifying database and user by OID. */
146extern void BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags);
147
148/*
149 * Flags to BackgroundWorkerInitializeConnection et al
150 *
151 *
152 * Allow bypassing datallowconn restrictions when connecting to database
153 */
154#define BGWORKER_BYPASS_ALLOWCONN 1
155
156
157/* Block/unblock signals in a background worker process */
158extern void BackgroundWorkerBlockSignals(void);
159extern void BackgroundWorkerUnblockSignals(void);
160
161#endif /* BGWORKER_H */
162