#       $Id: __init__.py,v 1.1.1.1 2005/06/27 08:37:21 dieter Exp $
'''ZEOKeepAlive.

Our cluster checks made us aware that 'ZEOClientStorage' depends
on the operating system to inform about connection breaks
and that this cannot do this reliably during inactivity periods.

This product starts a thread that periodically sends a keep alive
message to all ZEO connections. Sending will fail when the
connection is no longer intact triggering 'ZEOClientStorage's
automatic reconnect.

The thread is controlled by the environment variable
'ZEO_KEEPALIVE_PERIOD'. If not specified, the keep alive thread is
not started.

For use by non Zope ZEO clients, it defines the function
'startThread'. It has the optional argument 'period' specifying
the period (default: use value given by environment variable
'ZEO_KEEPALIVE_PERIOD').

As in 'ZEOClientStorage', we assume that no communication will hang, not
even under abnormal conditions. The solution would be much more
complex had we not made this assumption.

Logs

 We log as 'INFO' whether or not we start the keep alive thread.

 We log as 'WARNING' unready storages

 We log as 'BLATHER' send and response events for keep alive messages
'''

from os import environ
from time import sleep
from thread import start_new_thread

from zLOG import LOG, INFO, WARNING, BLATHER, ERROR, PANIC
from App.config import getConfiguration
from ZEO.ClientStorage import ClientStorage


_period = None

def startThread(period=None):
  global _period

  if _period:
    raise ValueError('KeepAlive thread already started')

  if period is None:
    period = environ.get('ZEO_KEEPALIVE_PERIOD')

  if period is not None: period = int(period)
  period = _period = period and period > 0 and period

  _log(INFO,
       period and 'Thread started with period %s sec' % period
       or 'Thread not started'
       )

  if period: start_new_thread(_keepAlive, (period,))
 

def initialize(context):
  startThread()


def _keepAlive(period):
  try:
    while True:
      sleep(period)
      dbs = getConfiguration().dbtab
      for db in dbs.opened.values():
        S = db._storage
        if isinstance(S, ClientStorage):
          name = S.getName()
          if S._ready.isSet():
            _log(BLATHER, "Sending keep alive for %s" % name)
            S._load_lock.acquire()
            try:
              try:
                S._server.get_info()
                _log(BLATHER, "Keep alive for %s successful" % name)
              except:
                _log(ERROR, "Keep alive for %s failed" % name, error=True)
            finally:
              S._load_lock.release()
          else: _log(WARNING, "Connection for %s is down" % name)
  except:
    _log(PANIC, "Exception in keep alive thread", error=True)


def _log(*args, **kw):
  LOG('ZEO KeepAlive', *args, **kw)