From aae5403278f995e240d956848cdf95fc173693ae Mon Sep 17 00:00:00 2001
From: Magnus Hagander <magnus@hagander.net>
Date: Mon, 4 Jun 2007 13:39:28 +0000
Subject: [PATCH] On win32, retry reading when WSARecv returns WSAEWOULDBLOCK.
 There seem to be cases when at least Windows 2000 can do this even though
 select just indicated that the socket is readable.

Per report and analysis from Cyril VELTER.
---
 src/backend/port/win32/socket.c | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/backend/port/win32/socket.c b/src/backend/port/win32/socket.c
index c7557034b7..3c6fbdb60d 100644
--- a/src/backend/port/win32/socket.c
+++ b/src/backend/port/win32/socket.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/win32/socket.c,v 1.17 2007/01/26 20:06:52 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/win32/socket.c,v 1.18 2007/06/04 13:39:28 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -291,6 +291,7 @@ pgwin32_recv(SOCKET s, char *buf, int len, int f)
 	int			r;
 	DWORD		b;
 	DWORD		flags = f;
+	int		n;
 
 	if (pgwin32_poll_signals())
 		return -1;
@@ -312,17 +313,36 @@ pgwin32_recv(SOCKET s, char *buf, int len, int f)
 
 	/* No error, zero bytes (win2000+) or error+WSAEWOULDBLOCK (<=nt4) */
 
-	if (pgwin32_waitforsinglesocket(s, FD_READ | FD_CLOSE | FD_ACCEPT,
-									INFINITE) == 0)
-		return -1;
-
-	r = WSARecv(s, &wbuf, 1, &b, &flags, NULL, NULL);
-	if (r == SOCKET_ERROR)
+	for (n = 0; n < 5; n++)
 	{
-		TranslateSocketError();
-		return -1;
+		if (pgwin32_waitforsinglesocket(s, FD_READ | FD_CLOSE | FD_ACCEPT,
+										INFINITE) == 0)
+			return -1; /* errno already set */
+	
+		r = WSARecv(s, &wbuf, 1, &b, &flags, NULL, NULL);
+		if (r == SOCKET_ERROR)
+		{
+			if (WSAGetLastError() == WSAEWOULDBLOCK)
+			{
+				/*
+				 * There seem to be cases on win2k (at least) where WSARecv
+				 * can return WSAEWOULDBLOCK even when pgwin32_waitforsinglesocket
+				 * claims the socket is readable. In this case, just sleep for a
+				 * moment and try again. We try up to 5 times - if it fails more than
+				 * that it's not likely to ever come back.
+				 */
+				pg_usleep(10000);
+				continue;
+			}
+			TranslateSocketError();
+			return -1;
+		}
+		return b;
 	}
-	return b;
+	ereport(NOTICE,
+		(errmsg_internal("Failed to read from ready socket (after retries)")));
+	errno = EWOULDBLOCK;
+	return -1;
 }
 
 int
-- 
2.11.0