From 4fc3fbec33557c4fc3ee9b700a9a0a7700f04948 Mon Sep 17 00:00:00 2001
From: Paul Fisher <pfisher@lyft.com>
Date: Mon, 11 Jan 2016 11:26:30 -0800
Subject: [PATCH] lock domain socket and remove on last arbiter exit

---
 gunicorn/sock.py | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/gunicorn/sock.py b/gunicorn/sock.py
index 4de972854..fdb5ae752 100644
--- a/gunicorn/sock.py
+++ b/gunicorn/sock.py
@@ -4,6 +4,7 @@
 # See the NOTICE for more information.
 
 import errno
+import fcntl
 import os
 import socket
 import stat
@@ -105,6 +106,8 @@ def __init__(self, addr, conf, log, fd=None):
                     raise ValueError("%r is not a socket" % addr)
         self.parent = os.getpid()
         super(UnixSocket, self).__init__(addr, conf, log, fd=fd)
+        # each arbiter grabs a shared lock on the unix socket.
+        fcntl.lockf(self.sock, fcntl.LOCK_SH | fcntl.LOCK_NB)
 
     def __str__(self):
         return "unix:%s" % self.cfg_addr
@@ -117,9 +120,17 @@ def bind(self, sock):
 
 
     def close(self):
-        super(UnixSocket, self).close()
         if self.parent == os.getpid():
-            os.unlink(self.cfg_addr)
+            # attempt to acquire an exclusive lock on the unix socket.
+            # if we're the only arbiter running, the lock will succeed, and
+            # we can safely rm the socket.
+            try:
+                fcntl.lockf(self.sock, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            except:
+                pass
+            else:
+                os.unlink(self.cfg_addr)
+        super(UnixSocket, self).close()
 
 
 def _sock_type(addr):