From 7392b68ccc2e091d353a3cba96c38d770121ec7e Mon Sep 17 00:00:00 2001
From: Paul Fisher <pfisher@lyft.com>
Date: Mon, 11 Jan 2016 11:26:30 -0800
Subject: [PATCH 1/2] 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 4de9728541..fdb5ae752e 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):

From 45d63301e2e896787661c0192d70e3032ff7cf76 Mon Sep 17 00:00:00 2001
From: Randall Leeds <randall@bleeds.info>
Date: Sun, 13 Mar 2016 15:56:22 -0700
Subject: [PATCH 2/2] add tests for arbiter unix socket locking

---
 tests/test_sock.py | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 tests/test_sock.py

diff --git a/tests/test_sock.py b/tests/test_sock.py
new file mode 100644
index 0000000000..aa094b9f78
--- /dev/null
+++ b/tests/test_sock.py
@@ -0,0 +1,56 @@
+import fcntl
+
+try:
+    import unittest.mock as mock
+except ImportError:
+    import mock
+
+from gunicorn import sock
+
+
+@mock.patch('fcntl.lockf')
+@mock.patch('socket.fromfd')
+def test_unix_socket_init_lock(fromfd, lockf):
+    s = fromfd.return_value
+    sock.UnixSocket('test.sock', mock.Mock(), mock.Mock(), mock.Mock())
+    lockf.assert_called_with(s, fcntl.LOCK_SH | fcntl.LOCK_NB)
+
+
+@mock.patch('fcntl.lockf')
+@mock.patch('os.getpid')
+@mock.patch('os.unlink')
+@mock.patch('socket.fromfd')
+def test_unix_socket_close_delete_if_exlock(fromfd, unlink, getpid, lockf):
+    s = fromfd.return_value
+    gsock = sock.UnixSocket('test.sock', mock.Mock(), mock.Mock(), mock.Mock())
+    lockf.reset_mock()
+    gsock.close()
+    lockf.assert_called_with(s, fcntl.LOCK_EX | fcntl.LOCK_NB)
+    unlink.assert_called_with('test.sock')
+
+
+@mock.patch('fcntl.lockf')
+@mock.patch('os.getpid')
+@mock.patch('os.unlink')
+@mock.patch('socket.fromfd')
+def test_unix_socket_close_keep_if_no_exlock(fromfd, unlink, getpid, lockf):
+    s = fromfd.return_value
+    gsock = sock.UnixSocket('test.sock', mock.Mock(), mock.Mock(), mock.Mock())
+    lockf.reset_mock()
+    lockf.side_effect = IOError('locked')
+    gsock.close()
+    lockf.assert_called_with(s, fcntl.LOCK_EX | fcntl.LOCK_NB)
+    unlink.assert_not_called()
+
+
+@mock.patch('fcntl.lockf')
+@mock.patch('os.getpid')
+@mock.patch('socket.fromfd')
+def test_unix_socket_not_deleted_by_worker(fromfd, getpid, lockf):
+    fd = mock.Mock()
+    gsock = sock.UnixSocket('name', mock.Mock(), mock.Mock(), fd)
+    lockf.reset_mock()
+    getpid.reset_mock()
+    getpid.return_value = mock.Mock()  # fake a pid change
+    gsock.close()
+    lockf.assert_not_called()