Always use connections in non-blocking mode.

Now that there's no blocking libpq callers left, default to using
non-blocking mode in connection_management.c.  This has two
advantages:
1) Blockiness doesn't have to frequently be reset, simplifying code
2) Prevents accidental use of blocking libpq functions, since they'll
   frequently return 'need IO'

src/backend/distributed/connection/connection_management.c

@@ -640,6 +640,13 @@ StartConnectionEstablishment(ConnectionHashKey *key)
 	connection->pgConn = PQconnectStartParams(keywords, values, false);
 	connection->connectionStart = GetCurrentTimestamp();
 
+	/*
+	 * To avoid issues with interrupts not getting caught all our connections
+	 * are managed in a non-blocking manner. remote_commands.c provides
+	 * wrappers emulating blocking behaviour.
+	 */
+	PQsetnonblocking(connection->pgConn, true);
+
 	return connection;
 }
 

src/backend/distributed/connection/remote_commands.c

@@ -280,7 +280,6 @@ SendRemoteCommandParams(MultiConnection *connection, const char *command,
 						const char *const *parameterValues)
 {
 	PGconn *pgConn = connection->pgConn;
-	bool wasNonblocking = false;
 	int rc = 0;
 
 	LogRemoteCommand(connection, command);
@@ -294,23 +293,11 @@ SendRemoteCommandParams(MultiConnection *connection, const char *command,
 		return 0;
 	}
 
-	wasNonblocking = PQisnonblocking(pgConn);
+	Assert(PQisnonblocking(pgConn));
-
-	/* make sure not to block anywhere */
-	if (!wasNonblocking)
-	{
-		PQsetnonblocking(pgConn, true);
-	}
 
 	rc = PQsendQueryParams(pgConn, command, parameterCount, parameterTypes,
 						   parameterValues, NULL, NULL, 0);
 
-	/* reset nonblocking connection to its original state */
-	if (!wasNonblocking)
-	{
-		PQsetnonblocking(pgConn, false);
-	}
-
 	return rc;
 }
 
@@ -380,7 +367,6 @@ PGresult *
 GetRemoteCommandResult(MultiConnection *connection, bool raiseInterrupts)
 {
 	PGconn *pgConn = connection->pgConn;
-	bool wasNonblocking = false;
 	PGresult *result = NULL;
 
 	/*
@@ -393,11 +379,6 @@ GetRemoteCommandResult(MultiConnection *connection, bool raiseInterrupts)
 		return PQgetResult(connection->pgConn);
 	}
 
-	wasNonblocking = PQisnonblocking(pgConn);
-
-	/* make sure not to block anywhere */
-	PQsetnonblocking(pgConn, true);
-
 	if (!FinishConnectionIO(connection, raiseInterrupts))
 	{
 		return NULL;
@@ -408,8 +389,6 @@ GetRemoteCommandResult(MultiConnection *connection, bool raiseInterrupts)
 
 	result = PQgetResult(connection->pgConn);
 
-	PQsetnonblocking(pgConn, wasNonblocking);
-
 	return result;
 }
 
@@ -424,38 +403,31 @@ bool
 PutRemoteCopyData(MultiConnection *connection, const char *buffer, int nbytes)
 {
 	PGconn *pgConn = connection->pgConn;
-	bool wasNonblocking = false;
 	int copyState = 0;
-	bool success = false;
 
 	if (PQstatus(pgConn) != CONNECTION_OK)
 	{
 		return false;
 	}
 
-	wasNonblocking = PQisnonblocking(pgConn);
+	Assert(PQisnonblocking(pgConn));
-
-	PQsetnonblocking(pgConn, true);
 
 	copyState = PQputCopyData(pgConn, buffer, nbytes);
 
 	if (copyState == 1)
 	{
 		/* successful */
-		success = true;
+		return true;
 	}
 	else if (copyState == -1)
 	{
-		success = false;
+		return false;
 	}
 	else
 	{
 		bool allowInterrupts = true;
-		success = FinishConnectionIO(connection, allowInterrupts);
+		return FinishConnectionIO(connection, allowInterrupts);
 	}
-
-	PQsetnonblocking(pgConn, wasNonblocking);
-	return success;
 }
 
 
@@ -469,38 +441,31 @@ bool
 PutRemoteCopyEnd(MultiConnection *connection, const char *errormsg)
 {
 	PGconn *pgConn = connection->pgConn;
-	bool wasNonblocking = false;
 	int copyState = 0;
-	bool success = false;
 
 	if (PQstatus(pgConn) != CONNECTION_OK)
 	{
 		return false;
 	}
 
-	wasNonblocking = PQisnonblocking(pgConn);
+	Assert(PQisnonblocking(pgConn));
-
-	PQsetnonblocking(pgConn, true);
 
 	copyState = PQputCopyEnd(pgConn, errormsg);
 
 	if (copyState == 1)
 	{
 		/* successful */
-		success = true;
+		return true;
 	}
 	else if (copyState == -1)
 	{
-		success = false;
+		return false;
 	}
 	else
 	{
 		bool allowInterrupts = true;
-		success = FinishConnectionIO(connection, allowInterrupts);
+		return FinishConnectionIO(connection, allowInterrupts);
 	}
-
-	PQsetnonblocking(pgConn, wasNonblocking);
-	return success;
 }