arbiter: clean up main loop

* Look up handlers in __init__() to induce run-time error early on if
  something is wrong.

* Since we now know that all handlers exist, we can simplify the main
  loop in arbiter, in such a way that we don't need to call wakeup().

So after this commit, the pipe in arbiter is only used to deliver
which signal was sent.

gunicorn/arbiter.py

@@ -42,7 +42,6 @@ class Arbiter(object):
  SIG_QUEUE = queue.SimpleQueue()
  SIGNALS = [getattr(signal.Signals, "SIG%s" % x)
  for x in "CHLD HUP QUIT INT TERM TTIN TTOU USR1 USR2 WINCH".split()]
- SIG_NAMES = dict((sig, sig.name[3:].lower()) for sig in SIGNALS)
 
  def __init__(self, app):
  os.environ["SERVER_SOFTWARE"] = SERVER_SOFTWARE
@@ -72,6 +71,11 @@ def __init__(self, app):
  0: sys.executable
  }
 
+ self.SIG_HANDLERS = dict(
+ (sig, getattr(self, "handle_%s" % sig.name[3:].lower()))
+ for sig in self.SIGNALS
+ )
+
  def _get_num_workers(self):
  return self._num_workers
 
@@ -194,18 +198,11 @@ def run(self):
 
  try:
  sig = self.SIG_QUEUE.get(timeout=1)
- except queue.Empty:
- sig = None
-
- if sig:
- signame = self.SIG_NAMES.get(sig)
- handler = getattr(self, "handle_%s" % signame, None)
- if not handler:
- self.log.error("Unhandled signal: %s", signame)
- continue
  if sig != signal.SIGCHLD:
- self.log.info("Handling signal: %s", signame)
- handler()
+ self.log.info("Handling signal: %s", signal.Signals(sig).name)
+ self.SIG_HANDLERS[sig]()
+ except queue.Empty:
+ pass
 
  self.murder_workers()
  self.manage_workers()