Ensure that we retry rather than erroring out when send() or recv() return

EINTR; the stats code was failing to do this and so were a couple of places
in the postmaster.  The stats code assumed that recv() could not return EINTR
if a preceding select() showed the socket to be read-ready, but this is
demonstrably false with our Windows implementation of recv(), and it may
not be the case on all Unix variants either.  I think this explains the
intermittent stats regression test failures we've been seeing, as well
as reports of stats collector instability under high load on Windows.

Backpatch as far as 8.0.

src/backend/postmaster/pgstat.c

@@ -13,7 +13,7 @@
  *
  *	Copyright (c) 2001-2006, PostgreSQL Global Development Group
  *
- *	$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.135 2006/07/14 14:52:22 momjian Exp $
+ *	$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.136 2006/07/16 18:17:14 tgl Exp $
  * ----------
  */
 #include "postgres.h"
@@ -323,8 +323,12 @@ pgstat_init(void)
 		 * rules prevent it).
 		 */
 		test_byte = TESTBYTEVAL;
+
+retry1:
 		if (send(pgStatSock, &test_byte, 1, 0) != 1)
 		{
+			if (errno == EINTR)
+				goto retry1;	/* if interrupted, just retry */
 			ereport(LOG,
 					(errcode_for_socket_access(),
 					 errmsg("could not send test message on socket for statistics collector: %m")));
@@ -375,8 +379,11 @@ pgstat_init(void)
 
 		test_byte++;			/* just make sure variable is changed */
 
+retry2:
 		if (recv(pgStatSock, &test_byte, 1, 0) != 1)
 		{
+			if (errno == EINTR)
+				goto retry2;	/* if interrupted, just retry */
 			ereport(LOG,
 					(errcode_for_socket_access(),
 					 errmsg("could not receive test message on socket for statistics collector: %m")));
@@ -1533,17 +1540,23 @@ pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
 static void
 pgstat_send(void *msg, int len)
 {
+	int			rc;
+
 	if (pgStatSock < 0)
 		return;
 
 	((PgStat_MsgHdr *) msg)->m_size = len;
 
+	/* We'll retry after EINTR, but ignore all other failures */
+	do
+	{
+		rc = send(pgStatSock, msg, len, 0);
+	} while (rc < 0 && errno == EINTR);
+
 #ifdef USE_ASSERT_CHECKING
-	if (send(pgStatSock, msg, len, 0) < 0)
+	/* In debug builds, log send failures ... */
+	if (rc < 0)
 		elog(LOG, "could not send to statistics collector: %m");
-#else
-	send(pgStatSock, msg, len, 0);
-	/* We deliberately ignore any error from send() */
 #endif
 }
 
@@ -1718,9 +1731,13 @@ PgstatCollectorMain(int argc, char *argv[])
 			len = recv(pgStatSock, (char *) &msg,
 					   sizeof(PgStat_Msg), 0);
 			if (len < 0)
+			{
+				if (errno == EINTR)
+					continue;
 				ereport(ERROR,
 						(errcode_for_socket_access(),
 						 errmsg("could not read statistics message: %m")));
+			}
 
 			/*
 			 * We ignore messages that are smaller than our common header

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.494 2006/07/15 15:47:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.495 2006/07/16 18:17:14 tgl Exp $
  *
  * NOTES
  *
@@ -1374,8 +1374,12 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 #else
 		SSLok = 'N';			/* No support for SSL */
 #endif
+
+retry1:
 		if (send(port->sock, &SSLok, 1, 0) != 1)
 		{
+			if (errno == EINTR)
+				goto retry1;	/* if interrupted, just retry */
 			ereport(COMMERROR,
 					(errcode_for_socket_access(),
 					 errmsg("failed to send SSL negotiation response: %m")));
@@ -2524,6 +2528,7 @@ static void
 report_fork_failure_to_client(Port *port, int errnum)
 {
 	char		buffer[1000];
+	int			rc;
 
 	/* Format the error message packet (always V2 protocol) */
 	snprintf(buffer, sizeof(buffer), "E%s%s\n",
@@ -2534,7 +2539,11 @@ report_fork_failure_to_client(Port *port, int errnum)
 	if (!pg_set_noblock(port->sock))
 		return;
 
-	send(port->sock, buffer, strlen(buffer) + 1, 0);
+	/* We'll retry after EINTR, but ignore all other failures */
+	do
+	{
+		rc = send(port->sock, buffer, strlen(buffer) + 1, 0);
+	} while (rc < 0 && errno == EINTR);
 }