sfa/util/callids.py

   1 #!/usr/bin/env python2
   2
   3 import threading
   4 import time
   5
   6 from sfa.util.sfalogging import logger
   7
   8 """
   9 Callids: a simple mechanism to remember the call ids served so fas
  10 memory-only for now - thread-safe
  11 implemented as a (singleton) hash 'callid'->timestamp
  12 """
  13
  14 debug = False
  15
  16
  17 class _call_ids_impl (dict):
  18
  19     _instance = None
  20     # 5 minutes sounds amply enough
  21     purge_timeout = 5 * 60
  22     # when trying to get a lock
  23     retries = 10
  24     # in ms
  25     wait_ms = 100
  26
  27     def __init__(self):
  28         self._lock = threading.Lock()
  29
  30     # the only primitive
  31     # return True if the callid is unknown, False otherwise
  32     def already_handled(self, call_id):
  33         # if not provided in the call...
  34         if not call_id:
  35             return False
  36         has_lock = False
  37         for attempt in range(_call_ids_impl.retries):
  38             if debug:
  39                 logger.debug("Waiting for lock (%d)" % attempt)
  40             if self._lock.acquire(False):
  41                 has_lock = True
  42                 if debug:
  43                     logger.debug("got lock (%d)" % attempt)
  44                 break
  45             time.sleep(float(_call_ids_impl.wait_ms) / 1000)
  46         # in the unlikely event where we can't get the lock
  47         if not has_lock:
  48             logger.warning(
  49                 "_call_ids_impl.should_handle_call_id: could not acquire lock")
  50             return False
  51         # we're good to go
  52         if call_id in self:
  53             self._purge()
  54             self._lock.release()
  55             return True
  56         self[call_id] = time.time()
  57         self._purge()
  58         self._lock.release()
  59         if debug:
  60             logger.debug("released lock")
  61         return False
  62
  63     def _purge(self):
  64         now = time.time()
  65         o_keys = []
  66         for (k, v) in self.iteritems():
  67             if (now - v) >= _call_ids_impl.purge_timeout:
  68                 o_keys.append(k)
  69         for k in o_keys:
  70             if debug:
  71                 logger.debug("Purging call_id %r (%s)" % (
  72                     k, time.strftime("%H:%M:%S", time.localtime(self[k]))))
  73             del self[k]
  74         if debug:
  75             logger.debug("AFTER PURGE")
  76             for (k, v) in self.iteritems():
  77                 logger.debug("%s -> %s" %
  78                              (k, time.strftime("%H:%M:%S", time.localtime(v))))
  79
  80
  81 def Callids():
  82     if not _call_ids_impl._instance:
  83         _call_ids_impl._instance = _call_ids_impl()
  84     return _call_ids_impl._instance