Assorted bgworker-related comment fixes.

Per gripes by Amit Kapila.

src/backend/postmaster/bgworker.c

@@ -134,17 +134,15 @@ BackgroundWorkerShmemInit(void)
 		Assert(found);
 }
 
+/*
+ * Search the postmaster's backend-private list of RegisteredBgWorker objects
+ * for the one that maps to the given slot number.
+ */
 static RegisteredBgWorker *
 FindRegisteredWorkerBySlotNumber(int slotno)
 {
 	slist_iter	siter;
 
-	/*
-	 * Copy contents of worker list into shared memory.  Record the
-	 * shared memory slot assigned to each worker.  This ensures
-	 * a 1-to-1 correspondence betwen the postmaster's private list and
-	 * the array in shared memory.
-	 */
 	slist_foreach(siter, &BackgroundWorkerList)
 	{
 		RegisteredBgWorker *rw;
@@ -158,7 +156,7 @@ FindRegisteredWorkerBySlotNumber(int slotno)
 }
 
 /*
- * Notice changes to shared_memory made by other backends.  This code
+ * Notice changes to shared memory made by other backends.  This code
  * runs in the postmaster, so we must be very careful not to assume that
  * shared memory contents are sane.  Otherwise, a rogue backend could take
  * out the postmaster.

src/include/postmaster/bgworker.h

@@ -6,11 +6,13 @@
  * including normal transactions.
  *
  * Any external module loaded via shared_preload_libraries can register a
- * worker.	Then, at the appropriate time, the worker process is forked from
- * the postmaster and runs the user-supplied "main" function.  This code may
- * connect to a database and run transactions.	Once started, it stays active
- * until shutdown or crash.  The process should sleep during periods of
- * inactivity.
+ * worker.	Workers can also be registered dynamically at runtime.  In either
+ * case, the worker process is forked from the postmaster and runs the
+ * user-supplied "main" function.  This code may connect to a database and
+ * run transactions.  Once started, it stays active until shutdown or crash;
+ * unless the restart interval is declared as BGW_NEVER_RESTART and the
+ * process exits with a return code of 1; workers that do this are
+ * automatically unregistered by the postmaster.
  *
  * If the fork() call fails in the postmaster, it will try again later.  Note
  * that the failure can only be transient (fork failure due to high load,