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

@@ -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;
@@ -312,18 +313,37 @@ pgwin32_recv(SOCKET s, char *buf, int len, int f)
 
 	/* No error, zero bytes (win2000+) or error+WSAEWOULDBLOCK (<=nt4) */
 
+	for (n = 0; n < 5; n++)
+	{
 		if (pgwin32_waitforsinglesocket(s, FD_READ | FD_CLOSE | FD_ACCEPT,
 										INFINITE) == 0)
-		return -1;
+			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;
 	}
+	ereport(NOTICE,
+		(errmsg_internal("Failed to read from ready socket (after retries)")));
+	errno = EWOULDBLOCK;
+	return -1;
+}
 
 int
 pgwin32_send(SOCKET s, char *buf, int len, int flags)