[Xen-devel] [PATCH 2/2] Make sure that TCP binds don't fail because of stale state

[Anthony Liguori <aliguori@xxxxxxxxxx>]

SO_REUSEADDR does not immediately free up a port when a server is killed 
with a signal (which is what we do for xend stop).  Since there is no 
great way (at least, that I know of) to deal with this, the following 
patch implements a 30 second timeout for bind to help make it highly 
unlikely that we'll get burned by this.
On a very slow system, killing xend with a signal takes less than a 
second for the port to become available again so 30 seconds seems really 
safe.  With this patch (and the previous one), I can execute the following:
while true; do xend restart && xm list || break; done

And it runs without any trouble (I ran it for an hour before finally 
giving up).
Regards,

Anthony Liguori

# HG changeset patch
# User anthony@xxxxxxxxxxxxxxxxxxxxx
# Node ID 13d6ca9c35dd02770901b9a8f9f2e53c7ed500c5
# Parent  8c866d412673e4169386ee5c96ba10f20f54bf6c
SO_REUSEADDR is not enough to ensure we don't get address in use errors when
xend dies from a signal.

We implement a 30 second time to ensure we don't fail if we don't have to.

Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>

diff -r 8c866d412673 -r 13d6ca9c35dd tools/python/xen/web/tcp.py
--- a/tools/python/xen/web/tcp.py       Wed Sep 14 23:47:37 2005
+++ b/tools/python/xen/web/tcp.py       Thu Sep 15 00:58:12 2005
@@ -18,6 +18,7 @@
 import sys
 import socket
 import types
+import time
 
 from connection import *
 from protocol import *
@@ -35,8 +36,25 @@
     def createSocket(self):
         sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-        addr = (self.interface, self.port)
-        sock.bind(addr)
+
+        # SO_REUSEADDR does not always ensure that we do not get an address
+        # in use error when restarted quickly
+        # we implement a timeout to try and avoid failing unnecessarily
+
+        timeout = time.time() + 30
+        again = True
+        while again and time.time() < timeout:
+            again = False
+            try:
+                sock.bind((self.interface, self.port))
+            except socket.error, (errno, strerrno):
+                if errno == 98:
+                    again = True
+                else:
+                    raise socket.error(errno, strerrno)
+        if again:
+            raise socket.error(98, "address in use")
+                
         return sock
 
     def acceptConnection(self, sock, protocol, addr):

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