Refactor how InitProcess is called

The order of process initialization steps is now more consistent
between !EXEC_BACKEND and EXEC_BACKEND modes. InitProcess() is called
at the same place in either mode. We can now also move the
AttachSharedMemoryStructs() call into InitProcess() itself. This
reduces the number of "#ifdef EXEC_BACKEND" blocks.

Reviewed-by: Tristan Partin, Andres Freund, Alexander Lakhin
Discussion: https://www.postgresql.org/message-id/7a59b073-5b5b-151e-7ed3-8b01ff7ce9ef@iki.fi

src/backend/postmaster/autovacuum.c

@@ -476,14 +476,10 @@ AutoVacLauncherMain(int argc, char *argv[])
 	pqsignal(SIGCHLD, SIG_DFL);
 
 	/*
-	 * Create a per-backend PGPROC struct in shared memory, except in the
+	 * Create a per-backend PGPROC struct in shared memory.  We must do this
-	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
+	 * before we can use LWLocks or access any shared memory.
-	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
-	 * had to do some stuff with LWLocks).
 	 */
-#ifndef EXEC_BACKEND
 	InitProcess();
-#endif
 
 	/* Early initialization */
 	BaseInit();
@@ -1548,14 +1544,10 @@ AutoVacWorkerMain(int argc, char *argv[])
 	pqsignal(SIGCHLD, SIG_DFL);
 
 	/*
-	 * Create a per-backend PGPROC struct in shared memory, except in the
+	 * Create a per-backend PGPROC struct in shared memory.  We must do this
-	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
+	 * before we can use LWLocks or access any shared memory.
-	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
-	 * had to do some stuff with LWLocks).
 	 */
-#ifndef EXEC_BACKEND
 	InitProcess();
-#endif
 
 	/* Early initialization */
 	BaseInit();

src/backend/postmaster/auxprocess.c

@@ -97,12 +97,9 @@ AuxiliaryProcessMain(AuxProcType auxtype)
 	 */
 
 	/*
-	 * Create a PGPROC so we can use LWLocks.  In the EXEC_BACKEND case, this
+	 * Create a PGPROC so we can use LWLocks and access shared memory.
-	 * was already done by SubPostmasterMain().
 	 */
-#ifndef EXEC_BACKEND
 	InitAuxiliaryProcess();
-#endif
 
 	BaseInit();
 

src/backend/postmaster/bgworker.c

@@ -810,14 +810,10 @@ BackgroundWorkerMain(void)
 	PG_exception_stack = &local_sigjmp_buf;
 
 	/*
-	 * Create a per-backend PGPROC struct in shared memory, except in the
+	 * Create a per-backend PGPROC struct in shared memory.  We must do this
-	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
+	 * before we can use LWLocks or access any shared memory.
-	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
-	 * had to do some stuff with LWLocks).
 	 */
-#ifndef EXEC_BACKEND
 	InitProcess();
-#endif
 
 	/*
 	 * Early initialization.

src/backend/postmaster/postmaster.c

@@ -4100,15 +4100,6 @@ BackendStartup(Port *port)
 		/* Perform additional initialization and collect startup packet */
 		BackendInitialize(port);
 
-		/*
-		 * Create a per-backend PGPROC struct in shared memory. We must do
-		 * this before we can use LWLocks. In the !EXEC_BACKEND case (here)
-		 * this could be delayed a bit further, but EXEC_BACKEND needs to do
-		 * stuff with LWLocks before PostgresMain(), so we do it here as well
-		 * for symmetry.
-		 */
-		InitProcess();
-
 		/* And run the backend */
 		BackendRun(port);
 	}
@@ -4419,6 +4410,12 @@ BackendInitialize(Port *port)
 static void
 BackendRun(Port *port)
 {
+	/*
+	 * Create a per-backend PGPROC struct in shared memory.  We must do this
+	 * before we can use LWLocks or access any shared memory.
+	 */
+	InitProcess();
+
 	/*
 	 * Make sure we aren't in PostmasterContext anymore.  (We can't delete it
 	 * just yet, though, because InitPostgres will need the HBA data.)
@@ -4918,12 +4915,6 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Restore basic shared memory pointers */
 		InitShmemAccess(UsedShmemSegAddr);
 
-		/* Need a PGPROC to run AttachSharedMemoryStructs */
-		InitProcess();
-
-		/* Attach process to shared data structures */
-		AttachSharedMemoryStructs();
-
 		/* And run the backend */
 		BackendRun(port);		/* does not return */
 	}
@@ -4936,12 +4927,6 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Restore basic shared memory pointers */
 		InitShmemAccess(UsedShmemSegAddr);
 
-		/* Need a PGPROC to run AttachSharedMemoryStructs */
-		InitAuxiliaryProcess();
-
-		/* Attach process to shared data structures */
-		AttachSharedMemoryStructs();
-
 		auxtype = atoi(argv[3]);
 		AuxiliaryProcessMain(auxtype);	/* does not return */
 	}
@@ -4950,12 +4935,6 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Restore basic shared memory pointers */
 		InitShmemAccess(UsedShmemSegAddr);
 
-		/* Need a PGPROC to run AttachSharedMemoryStructs */
-		InitProcess();
-
-		/* Attach process to shared data structures */
-		AttachSharedMemoryStructs();
-
 		AutoVacLauncherMain(argc - 2, argv + 2);	/* does not return */
 	}
 	if (strcmp(argv[1], "--forkavworker") == 0)
@@ -4963,12 +4942,6 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Restore basic shared memory pointers */
 		InitShmemAccess(UsedShmemSegAddr);
 
-		/* Need a PGPROC to run AttachSharedMemoryStructs */
-		InitProcess();
-
-		/* Attach process to shared data structures */
-		AttachSharedMemoryStructs();
-
 		AutoVacWorkerMain(argc - 2, argv + 2);	/* does not return */
 	}
 	if (strcmp(argv[1], "--forkbgworker") == 0)
@@ -4979,12 +4952,6 @@ SubPostmasterMain(int argc, char *argv[])
 		/* Restore basic shared memory pointers */
 		InitShmemAccess(UsedShmemSegAddr);
 
-		/* Need a PGPROC to run AttachSharedMemoryStructs */
-		InitProcess();
-
-		/* Attach process to shared data structures */
-		AttachSharedMemoryStructs();
-
 		MyBgworkerEntry = worker;
 		BackgroundWorkerMain();
 	}

src/backend/storage/lmgr/proc.c

@@ -291,7 +291,7 @@ InitProcGlobal(void)
 }
 
 /*
- * InitProcess -- initialize a per-process data structure for this backend
+ * InitProcess -- initialize a per-process PGPROC entry for this backend
  */
 void
 InitProcess(void)
@@ -461,6 +461,16 @@ InitProcess(void)
 	 */
 	InitLWLockAccess();
 	InitDeadLockChecking();
+
+#ifdef EXEC_BACKEND
+
+	/*
+	 * Initialize backend-local pointers to all the shared data structures.
+	 * (We couldn't do this until now because it needs LWLocks.)
+	 */
+	if (IsUnderPostmaster)
+		AttachSharedMemoryStructs();
+#endif
 }
 
 /*
@@ -487,7 +497,7 @@ InitProcessPhase2(void)
 }
 
 /*
- * InitAuxiliaryProcess -- create a per-auxiliary-process data structure
+ * InitAuxiliaryProcess -- create a PGPROC entry for an auxiliary process
  *
  * This is called by bgwriter and similar processes so that they will have a
  * MyProc value that's real enough to let them wait for LWLocks.  The PGPROC
@@ -621,6 +631,16 @@ InitAuxiliaryProcess(void)
 	 * acquired in aux processes.)
 	 */
 	InitLWLockAccess();
+
+#ifdef EXEC_BACKEND
+
+	/*
+	 * Initialize backend-local pointers to all the shared data structures.
+	 * (We couldn't do this until now because it needs LWLocks.)
+	 */
+	if (IsUnderPostmaster)
+		AttachSharedMemoryStructs();
+#endif
 }
 
 /*