Protect some initializations from being called during backend startup.

On EXEC_BACKEND builds these functions shouldn't be called at every
backend start.

src/backend/distributed/shared_library_init.c

@@ -170,8 +170,13 @@ _PG_init(void)
 	/*
 	 * Extend the database directory structure before continuing with
 	 * initialization - one of the later steps might require them to exist.
+	 * If in a sub-process (windows / EXEC_BACKEND) this already has been
+	 * done.
 	 */
+	if (!IsUnderPostmaster)
+	{
 		CreateRequiredDirectories();
+	}
 
 	/*
 	 * Register Citus configuration variables. Do so before intercepting

src/backend/distributed/transaction/backend_data.c

@@ -297,7 +297,10 @@ void
 InitializeBackendManagement(void)
 {
 	/* allocate shared memory */
+	if (!IsUnderPostmaster)
+	{
 		RequestAddinShmemSpace(BackendManagementShmemSize());
+	}
 
 	prev_shmem_startup_hook = shmem_startup_hook;
 	shmem_startup_hook = BackendManagementShmemInit;

src/backend/distributed/utils/maintenanced.c

@@ -106,8 +106,11 @@ static bool LockCitusExtension(void);
  */
 void
 InitializeMaintenanceDaemon(void)
+{
+	if (!IsUnderPostmaster)
 	{
 		RequestAddinShmemSpace(MaintenanceDaemonShmemSize());
+	}
 
 	prev_shmem_startup_hook = shmem_startup_hook;
 	shmem_startup_hook = MaintenanceDaemonShmemInit;

src/backend/distributed/worker/task_tracker.c

@@ -100,12 +100,17 @@ TaskTrackerRegister(void)
 {
 	BackgroundWorker worker;
 
-	/* organize and register initialization of required shared memory */
-	RequestAddinShmemSpace(TaskTrackerShmemSize());
-
 	prev_shmem_startup_hook = shmem_startup_hook;
 	shmem_startup_hook = TaskTrackerShmemInit;
 
+	if (IsUnderPostmaster)
+	{
+		return;
+	}
+
+	/* organize and register initialization of required shared memory */
+	RequestAddinShmemSpace(TaskTrackerShmemSize());
+
 	/* and that the task tracker is started as background worker */
 	memset(&worker, 0, sizeof(worker));
 	worker.bgw_flags = BGWORKER_SHMEM_ACCESS;