sfa/util/callids.py

   1 #!/usr/bin/python
   2
   3 import threading
   4 import time
   5
   6 from sfa.util.sfalogging import sfa_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 class _call_ids_impl (dict):
  15
  16     _instance = None
  17     # 5 minutes sounds amply enough
  18     purge_timeout=5*60
  19     # when trying to get a lock
  20     retries=8
  21     # in ms
  22     wait_ms=200
  23
  24     def __init__(self):
  25         self._lock=threading.Lock()
  26
  27     # the only primitive
  28     # return True if the callid is unknown, False otherwise
  29     def should_handle_call_id (self,call_id):
  30         # if not provided in the call...
  31         if not call_id: return True
  32         has_lock=False
  33         for attempt in range(_call_ids_impl.retries):
  34             sfa_logger().debug("Waiting for lock (%d)"%attempt)
  35             if self._lock.acquire(False):
  36                 has_lock=True
  37                 sfa_logger().debug("got lock (%d)"%attempt)
  38                 break
  39             time.sleep(float(_call_ids_impl.wait_ms)/1000)
  40         # in the unlikely event where we can't get the lock
  41         if not has_lock:
  42             sfa_logger().warning("_call_ids_impl.should_handle_call_id: could not acquire lock")
  43             return True
  44         # we're good to go
  45         if self.has_key(call_id):
  46             self._purge()
  47             self._lock.release()
  48             return False
  49         self[call_id]=time.time()
  50         self._purge()
  51         self._lock.release()
  52         sfa_logger().debug("released lock")
  53         return True
  54
  55     def _purge(self):
  56         now=time.time()
  57         o_keys=[]
  58         for (k,v) in self.iteritems():
  59             if (now-v) >= _call_ids_impl.purge_timeout: o_keys.append(k)
  60         for k in o_keys:
  61             sfa_logger().debug("Purging call_id %r (%s)"%(k,time.strftime("%H:%M:%S",time.localtime(self[k]))))
  62             del self[k]
  63         sfa_logger().debug("AFTER PURGE")
  64         for (k,v) in self.iteritems(): sfa_logger().debug("%s -> %s"%(k,time.strftime("%H:%M:%S",time.localtime(v))))
  65
  66 def Callids ():
  67     if not _call_ids_impl._instance:
  68         _call_ids_impl._instance = _call_ids_impl()
  69     return _call_ids_impl._instance