From 9dfdbef345390124eaf993f6289e8ae796aa6918 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 19 Oct 2003 21:36:41 +0000
Subject: [PATCH] Adjust libpq to avoid deadlock when both client and server
 want to send data, and both have filled the transmission buffers.  One
 scenario where this can happen was illustrated here:
 http://archives.postgresql.org/pgsql-hackers/2003-04/msg00979.php

---
 src/interfaces/libpq/fe-exec.c | 13 ++++++++++++-
 src/interfaces/libpq/fe-misc.c | 21 +++++++++++++++++++--
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 810a753ed3..1967d7429b 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.151 2003/10/04 21:05:21 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.152 2003/10/19 21:36:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1336,6 +1336,17 @@ PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
 						  libpq_gettext("no COPY in progress\n"));
 		return -1;
 	}
+
+	/*
+	 * Check for NOTICE messages coming back from the server.  Since the
+	 * server might generate multiple notices during the COPY, we have to
+	 * consume those in a reasonably prompt fashion to prevent the comm
+	 * buffers from filling up and possibly blocking the server.
+	 */
+	if (!PQconsumeInput(conn))
+		return -1;				/* I/O failure */
+	parseInput(conn);
+
 	if (nbytes > 0)
 	{
 		/*
diff --git a/src/interfaces/libpq/fe-misc.c b/src/interfaces/libpq/fe-misc.c
index d71473d514..4349a4e05a 100644
--- a/src/interfaces/libpq/fe-misc.c
+++ b/src/interfaces/libpq/fe-misc.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.102 2003/08/08 21:42:55 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-misc.c,v 1.103 2003/10/19 21:36:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -828,7 +828,24 @@ pqSendSome(PGconn *conn, int len)
 				break;
 			}
 
-			if (pqWait(FALSE, TRUE, conn))
+			/*
+			 * There are scenarios in which we can't send data because the
+			 * communications channel is full, but we cannot expect the server
+			 * to clear the channel eventually because it's blocked trying to
+			 * send data to us.  (This can happen when we are sending a large
+			 * amount of COPY data, and the server has generated lots of
+			 * NOTICE responses.)  To avoid a deadlock situation, we must be
+			 * prepared to accept and buffer incoming data before we try
+			 * again.  Furthermore, it is possible that such incoming data
+			 * might not arrive until after we've gone to sleep.  Therefore,
+			 * we wait for either read ready or write ready.
+			 */
+			if (pqReadData(conn) < 0)
+			{
+				result = -1;	/* error message already set up */
+				break;
+			}
+			if (pqWait(TRUE, TRUE, conn))
 			{
 				result = -1;
 				break;
-- 
2.40.0