fix unix socket locking

This change add proper file locking to gunicorn. By default "gunicorn.lock" is created in the temporary directory when a unix socket is bound.  In case someone want to fix the lock file path or use multiple gunicorn instance the "--lock-file" setting can be used to set the path of this file.

fix #1259

gunicorn/arbiter.py

@@ -14,6 +14,7 @@
 import traceback
 
 from gunicorn.errors import HaltServer, AppImportError
+from gunicorn.lockfile import LockFile
 from gunicorn.pidfile import Pidfile
 from gunicorn.sock import create_sockets
 from gunicorn import util
@@ -39,6 +40,7 @@ class Arbiter(object):
     START_CTX = {}
 
     LISTENERS = []
+    LOCK_FILE = None
     WORKERS = {}
     PIPE = []
 
@@ -131,8 +133,16 @@ def start(self):
         self.cfg.on_starting(self)
 
         self.init_signals()
+        need_lock = False
         if not self.LISTENERS:
-            self.LISTENERS = create_sockets(self.cfg, self.log)
+            self.LISTENERS, need_lock = create_sockets(self.cfg, self.log)
+
+        self.log.info("lock file is needed %s", need_lock)
+        if need_lock:
+            self.log.info("%s created", self.cfg.lockfile)
+            if not self.LOCK_FILE:
+                self.LOCK_FILE = LockFile(self.cfg)
+            self.LOCK_FILE.lock()
 
         listeners_str = ",".join([str(l) for l in self.LISTENERS])
         self.log.debug("Arbiter booted")
@@ -335,8 +345,13 @@ def stop(self, graceful=True):
         :attr graceful: boolean, If True (the default) workers will be
         killed gracefully  (ie. trying to wait for the current connection)
         """
+        locked = False
+        if self.LOCK_FILE:
+            self.LOCK_FILE.unlock()
+            locked = self.LOCK_FILE.locked()
+
         for l in self.LISTENERS:
-            l.close()
+            l.close(locked)
         self.LISTENERS = []
         sig = signal.SIGTERM
         if not graceful: