Remove set_latch_on_sigusr1 flag.

This flag has proven to be a recipe for bugs, and it doesn't seem like
it can really buy anything in terms of performance.  So let's just
*always* set the process latch when we receive SIGUSR1 instead of
trying to do it only when needed.

Per my recent proposal on pgsql-hackers.

src/backend/postmaster/bgworker.c

@@ -954,13 +954,7 @@ WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
 {
 	BgwHandleStatus status;
 	int			rc;
-	bool		save_set_latch_on_sigusr1;
 
-	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
-	set_latch_on_sigusr1 = true;
-
-	PG_TRY();
-	{
 	for (;;)
 	{
 		pid_t		pid;
@@ -984,15 +978,7 @@ WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
 
 		ResetLatch(MyLatch);
 	}
-	}
-	PG_CATCH();
-	{
-		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
 
-	set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
 	return status;
 }
 
@@ -1009,13 +995,7 @@ WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
 {
 	BgwHandleStatus status;
 	int			rc;
-	bool		save_set_latch_on_sigusr1;
 
-	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
-	set_latch_on_sigusr1 = true;
-
-	PG_TRY();
-	{
 	for (;;)
 	{
 		pid_t		pid;
@@ -1034,15 +1014,7 @@ WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
 
 		ResetLatch(&MyProc->procLatch);
 	}
-	}
-	PG_CATCH();
-	{
-		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
 
-	set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
 	return status;
 }
 

src/backend/storage/ipc/procsignal.c

@@ -59,14 +59,6 @@ typedef struct
  */
 #define NumProcSignalSlots	(MaxBackends + NUM_AUXPROCTYPES)
 
-/*
- * If this flag is set, the process latch will be set whenever SIGUSR1
- * is received.  This is useful when waiting for a signal from the postmaster.
- * Spurious wakeups must be expected.  Make sure that the flag is cleared
- * in the error path.
- */
-bool		set_latch_on_sigusr1;
-
 static ProcSignalSlot *ProcSignalSlots = NULL;
 static volatile ProcSignalSlot *MyProcSignalSlot = NULL;
 
@@ -296,7 +288,6 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
-	if (set_latch_on_sigusr1)
 	SetLatch(MyLatch);
 
 	latch_sigusr1_handler();

src/backend/storage/ipc/shm_mq.c

@@ -962,15 +962,8 @@ static bool
 shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
 					 BackgroundWorkerHandle *handle)
 {
-	bool		save_set_latch_on_sigusr1;
 	bool		result = false;
 
-	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
-	if (handle != NULL)
-		set_latch_on_sigusr1 = true;
-
-	PG_TRY();
-	{
 	for (;;)
 	{
 		BgwHandleStatus status;
@@ -1012,13 +1005,6 @@ shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
 		/* Reset the latch so we don't spin. */
 		ResetLatch(MyLatch);
 	}
-	}
-	PG_CATCH();
-	{
-		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
 
 	return result;
 }

src/backend/tcop/postgres.c

@@ -2825,9 +2825,7 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	/*
 	 * Set the process latch. This function essentially emulates signal
 	 * handlers like die() and StatementCancelHandler() and it seems prudent
-	 * to behave similarly as they do. Alternatively all plain backend code
+	 * to behave similarly as they do.
-	 * waiting on that latch, expecting to get interrupted by query cancels et
-	 * al., would also need to set set_latch_on_sigusr1.
 	 */
 	SetLatch(MyLatch);
 

src/include/storage/procsignal.h

@@ -55,6 +55,5 @@ extern int SendProcSignal(pid_t pid, ProcSignalReason reason,
 			   BackendId backendId);
 
 extern void procsignal_sigusr1_handler(SIGNAL_ARGS);
-extern PGDLLIMPORT bool set_latch_on_sigusr1;
 
 #endif   /* PROCSIGNAL_H */

src/test/modules/test_shm_mq/setup.c

@@ -255,14 +255,8 @@ static void
 wait_for_workers_to_become_ready(worker_state *wstate,
 								 volatile test_shm_mq_header *hdr)
 {
-	bool		save_set_latch_on_sigusr1;
 	bool		result = false;
 
-	save_set_latch_on_sigusr1 = set_latch_on_sigusr1;
-	set_latch_on_sigusr1 = true;
-
-	PG_TRY();
-	{
 	for (;;)
 	{
 		int			workers_ready;
@@ -293,13 +287,6 @@ wait_for_workers_to_become_ready(worker_state *wstate,
 		/* Reset the latch so we don't spin. */
 		ResetLatch(MyLatch);
 	}
-	}
-	PG_CATCH();
-	{
-		set_latch_on_sigusr1 = save_set_latch_on_sigusr1;
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
 
 	if (!result)
 		ereport(ERROR,