Add background worker type

Add bgw_type field to background worker structure.  It is intended to be
set to the same value for all workers of the same type, so they can be
grouped in pg_stat_activity, for example.

The backend_type column in pg_stat_activity now shows bgw_type for a
background worker.  The ps listing also no longer calls out that a
process is a background worker but just show the bgw_type.  That way,
being a background worker is more of an implementation detail now that
is not shown to the user.  However, most log messages still refer to
'background worker "%s"'; otherwise constructing sensible and
translatable log messages would become tricky.

Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>

src/backend/postmaster/bgworker.c

@@ -344,6 +344,8 @@ BackgroundWorkerStateChange(void)
 		 */
 		ascii_safe_strlcpy(rw->rw_worker.bgw_name,
 						   slot->worker.bgw_name, BGW_MAXLEN);
+		ascii_safe_strlcpy(rw->rw_worker.bgw_type,
+						   slot->worker.bgw_type, BGW_MAXLEN);
 		ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
 						   slot->worker.bgw_library_name, BGW_MAXLEN);
 		ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
@@ -630,6 +632,12 @@ SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
 		return false;
 	}
 
+	/*
+	 * If bgw_type is not filled in, use bgw_name.
+	 */
+	if (strcmp(worker->bgw_type, "") == 0)
+		strcpy(worker->bgw_type, worker->bgw_name);
+
 	return true;
 }
 
@@ -671,7 +679,7 @@ bgworker_die(SIGNAL_ARGS)
 	ereport(FATAL,
 			(errcode(ERRCODE_ADMIN_SHUTDOWN),
 			 errmsg("terminating background worker \"%s\" due to administrator command",
-					MyBgworkerEntry->bgw_name)));
+					MyBgworkerEntry->bgw_type)));
 }
 
 /*
@@ -700,7 +708,6 @@ void
 StartBackgroundWorker(void)
 {
 	sigjmp_buf	local_sigjmp_buf;
-	char		buf[MAXPGPATH];
 	BackgroundWorker *worker = MyBgworkerEntry;
 	bgworker_main_type entrypt;
 
@@ -710,8 +717,7 @@ StartBackgroundWorker(void)
 	IsBackgroundWorker = true;
 
 	/* Identify myself via ps */
-	snprintf(buf, MAXPGPATH, "bgworker: %s", worker->bgw_name);
-	init_ps_display(buf, "", "", "");
+	init_ps_display(worker->bgw_name, "", "", "");
 
 	/*
 	 * If we're not supposed to have shared memory access, then detach from
@@ -1233,3 +1239,40 @@ LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname)
 	return (bgworker_main_type)
 		load_external_function(libraryname, funcname, true, NULL);
 }
+
+/*
+ * Given a PID, get the bgw_type of the background worker.  Returns NULL if
+ * not a valid background worker.
+ *
+ * The return value is in static memory belonging to this function, so it has
+ * to be used before calling this function again.  This is so that the caller
+ * doesn't have to worry about the background worker locking protocol.
+ */
+const char *
+GetBackgroundWorkerTypeByPid(pid_t pid)
+{
+	int			slotno;
+	bool		found = false;
+	static char	result[BGW_MAXLEN];
+
+	LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
+
+	for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
+	{
+		BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
+
+		if (slot->pid > 0 && slot->pid == pid)
+		{
+			strcpy(result, slot->worker.bgw_type);
+			found = true;
+			break;
+		}
+	}
+
+	LWLockRelease(BackgroundWorkerLock);
+
+	if (!found)
+		return NULL;
+
+	return result;
+}

src/backend/postmaster/postmaster.c

@@ -3117,8 +3117,9 @@ CleanupBackgroundWorker(int pid,
 			exitstatus = 0;
 #endif
 
-		snprintf(namebuf, MAXPGPATH, "%s: %s", _("worker process"),
-				 rw->rw_worker.bgw_name);
+		snprintf(namebuf, MAXPGPATH, _("background worker \"%s\""),
+				 rw->rw_worker.bgw_type);
+
 
 		if (!EXIT_STATUS_0(exitstatus))
 		{