Server-side fix for delayed NOTIFY and SIGTERM processing.

Commit 4f85fde8e introduced some code that was meant to ensure that we'd
process cancel, die, sinval catchup, and notify interrupts while waiting
for client input.  But there was a flaw: it supposed that the process
latch would be set upon arrival at secure_read() if any such interrupt
was pending.  In reality, we might well have cleared the process latch
at some earlier point while those flags remained set -- particularly
notifyInterruptPending, which can't be handled as long as we're within
a transaction.

To fix the NOTIFY case, also attempt to process signals (except
ProcDiePending) before trying to read.

Also, if we see that ProcDiePending is set before we read, forcibly set the
process latch to ensure that we will handle that signal promptly if no data
is available.  I also made it set the process latch on the way out, in case
there is similar logic elsewhere.  (It remains true that we won't service
ProcDiePending here unless we need to wait for input.)

The code for handling ProcDiePending during a write needs those changes,
too.

Also be a little more careful about when to reset whereToSendOutput,
and improve related comments.

Back-patch to 9.5 where this code was added.  I'm not entirely convinced
that older branches don't have similar issues, but the complaint at hand
is just about the >= 9.5 code.

Jeff Janes and Tom Lane

Discussion: https://postgr.es/m/CAOYf6ec-TmRYjKBXLLaGaB-jrd=mjG1Hzn1a1wufUAR39PQYhw@mail.gmail.com

1 files changed, 12 insertions, 8 deletions

diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index d349d7c2c72..4eb21fe89de 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -145,6 +145,9 @@ secure_read(Port *port, void *ptr, size_t len)
 	ssize_t		n;
 	int			waitfor;
 
+	/* Deal with any already-pending interrupt condition. */
+	ProcessClientReadInterrupt(false);
+
 retry:
 #ifdef USE_SSL
 	waitfor = 0;
@@ -209,9 +212,8 @@ retry:
 	}
 
 	/*
-	 * Process interrupts that happened while (or before) receiving. Note that
-	 * we signal that we're not blocking, which will prevent some types of
-	 * interrupts from being processed.
+	 * Process interrupts that happened during a successful (or non-blocking,
+	 * or hard-failed) read.
 	 */
 	ProcessClientReadInterrupt(false);
 
@@ -248,6 +250,9 @@ secure_write(Port *port, void *ptr, size_t len)
 	ssize_t		n;
 	int			waitfor;
 
+	/* Deal with any already-pending interrupt condition. */
+	ProcessClientWriteInterrupt(false);
+
 retry:
 	waitfor = 0;
 #ifdef USE_SSL
@@ -287,17 +292,16 @@ retry:
 
 			/*
 			 * We'll retry the write. Most likely it will return immediately
-			 * because there's still no data available, and we'll wait for the
-			 * socket to become ready again.
+			 * because there's still no buffer space available, and we'll wait
+			 * for the socket to become ready again.
 			 */
 		}
 		goto retry;
 	}
 
 	/*
-	 * Process interrupts that happened while (or before) sending. Note that
-	 * we signal that we're not blocking, which will prevent some types of
-	 * interrupts from being processed.
+	 * Process interrupts that happened during a successful (or non-blocking,
+	 * or hard-failed) write.
 	 */
 	ProcessClientWriteInterrupt(false);