/usr/share/pyshared/ovs/reconnect.py is in python-openvswitch 2.0.1+git20140120-0ubuntu2.
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#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at:
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import os
import ovs.vlog
import ovs.util
# Values returned by Reconnect.run()
CONNECT = 'connect'
DISCONNECT = 'disconnect'
PROBE = 'probe'
EOF = ovs.util.EOF
vlog = ovs.vlog.Vlog("reconnect")
class Reconnect(object):
"""A finite-state machine for connecting and reconnecting to a network
resource with exponential backoff. It also provides optional support for
detecting a connection on which the peer is no longer responding.
The library does not implement anything networking related, only an FSM for
networking code to use.
Many Reconnect methods take a "now" argument. This makes testing easier
since there is no hidden state. When not testing, just pass the return
value of ovs.time.msec(). (Perhaps this design should be revisited
later.)"""
class Void(object):
name = "VOID"
is_connected = False
@staticmethod
def deadline(fsm):
return None
@staticmethod
def run(fsm, now):
return None
class Listening(object):
name = "LISTENING"
is_connected = False
@staticmethod
def deadline(fsm):
return None
@staticmethod
def run(fsm, now):
return None
class Backoff(object):
name = "BACKOFF"
is_connected = False
@staticmethod
def deadline(fsm):
return fsm.state_entered + fsm.backoff
@staticmethod
def run(fsm, now):
return CONNECT
class ConnectInProgress(object):
name = "CONNECTING"
is_connected = False
@staticmethod
def deadline(fsm):
return fsm.state_entered + max(1000, fsm.backoff)
@staticmethod
def run(fsm, now):
return DISCONNECT
class Active(object):
name = "ACTIVE"
is_connected = True
@staticmethod
def deadline(fsm):
if fsm.probe_interval:
base = max(fsm.last_activity, fsm.state_entered)
return base + fsm.probe_interval
return None
@staticmethod
def run(fsm, now):
vlog.dbg("%s: idle %d ms, sending inactivity probe"
% (fsm.name,
now - max(fsm.last_activity, fsm.state_entered)))
fsm._transition(now, Reconnect.Idle)
return PROBE
class Idle(object):
name = "IDLE"
is_connected = True
@staticmethod
def deadline(fsm):
if fsm.probe_interval:
return fsm.state_entered + fsm.probe_interval
return None
@staticmethod
def run(fsm, now):
vlog.err("%s: no response to inactivity probe after %.3g "
"seconds, disconnecting"
% (fsm.name, (now - fsm.state_entered) / 1000.0))
return DISCONNECT
class Reconnect(object):
name = "RECONNECT"
is_connected = False
@staticmethod
def deadline(fsm):
return fsm.state_entered
@staticmethod
def run(fsm, now):
return DISCONNECT
def __init__(self, now):
"""Creates and returns a new reconnect FSM with default settings. The
FSM is initially disabled. The caller will likely want to call
self.enable() and self.set_name() on the returned object."""
self.name = "void"
self.min_backoff = 1000
self.max_backoff = 8000
self.probe_interval = 5000
self.passive = False
self.info_level = vlog.info
self.state = Reconnect.Void
self.state_entered = now
self.backoff = 0
self.last_activity = now
self.last_connected = None
self.last_disconnected = None
self.max_tries = None
self.creation_time = now
self.n_attempted_connections = 0
self.n_successful_connections = 0
self.total_connected_duration = 0
self.seqno = 0
def set_quiet(self, quiet):
"""If 'quiet' is true, this object will log informational messages at
debug level, by default keeping them out of log files. This is
appropriate if the connection is one that is expected to be
short-lived, so that the log messages are merely distracting.
If 'quiet' is false, this object logs informational messages at info
level. This is the default.
This setting has no effect on the log level of debugging, warning, or
error messages."""
if quiet:
self.info_level = vlog.dbg
else:
self.info_level = vlog.info
def get_name(self):
return self.name
def set_name(self, name):
"""Sets this object's name to 'name'. If 'name' is None, then "void"
is used instead.
The name is used in log messages."""
if name is None:
self.name = "void"
else:
self.name = name
def get_min_backoff(self):
"""Return the minimum number of milliseconds to back off between
consecutive connection attempts. The default is 1000 ms."""
return self.min_backoff
def get_max_backoff(self):
"""Return the maximum number of milliseconds to back off between
consecutive connection attempts. The default is 8000 ms."""
return self.max_backoff
def get_probe_interval(self):
"""Returns the "probe interval" in milliseconds. If this is zero, it
disables the connection keepalive feature. If it is nonzero, then if
the interval passes while the FSM is connected and without
self.activity() being called, self.run() returns ovs.reconnect.PROBE.
If the interval passes again without self.activity() being called,
self.run() returns ovs.reconnect.DISCONNECT."""
return self.probe_interval
def set_max_tries(self, max_tries):
"""Limits the maximum number of times that this object will ask the
client to try to reconnect to 'max_tries'. None (the default) means an
unlimited number of tries.
After the number of tries has expired, the FSM will disable itself
instead of backing off and retrying."""
self.max_tries = max_tries
def get_max_tries(self):
"""Returns the current remaining number of connection attempts,
None if the number is unlimited."""
return self.max_tries
def set_backoff(self, min_backoff, max_backoff):
"""Configures the backoff parameters for this FSM. 'min_backoff' is
the minimum number of milliseconds, and 'max_backoff' is the maximum,
between connection attempts.
'min_backoff' must be at least 1000, and 'max_backoff' must be greater
than or equal to 'min_backoff'."""
self.min_backoff = max(min_backoff, 1000)
if self.max_backoff:
self.max_backoff = max(max_backoff, 1000)
else:
self.max_backoff = 8000
if self.min_backoff > self.max_backoff:
self.max_backoff = self.min_backoff
if (self.state == Reconnect.Backoff and
self.backoff > self.max_backoff):
self.backoff = self.max_backoff
def set_probe_interval(self, probe_interval):
"""Sets the "probe interval" to 'probe_interval', in milliseconds. If
this is zero, it disables the connection keepalive feature. If it is
nonzero, then if the interval passes while this FSM is connected and
without self.activity() being called, self.run() returns
ovs.reconnect.PROBE. If the interval passes again without
self.activity() being called, self.run() returns
ovs.reconnect.DISCONNECT.
If 'probe_interval' is nonzero, then it will be forced to a value of at
least 1000 ms."""
if probe_interval:
self.probe_interval = max(1000, probe_interval)
else:
self.probe_interval = 0
def is_passive(self):
"""Returns true if 'fsm' is in passive mode, false if 'fsm' is in
active mode (the default)."""
return self.passive
def set_passive(self, passive, now):
"""Configures this FSM for active or passive mode. In active mode (the
default), the FSM is attempting to connect to a remote host. In
passive mode, the FSM is listening for connections from a remote
host."""
if self.passive != passive:
self.passive = passive
if ((passive and self.state in (Reconnect.ConnectInProgress,
Reconnect.Reconnect)) or
(not passive and self.state == Reconnect.Listening
and self.__may_retry())):
self._transition(now, Reconnect.Backoff)
self.backoff = 0
def is_enabled(self):
"""Returns true if this FSM has been enabled with self.enable().
Calling another function that indicates a change in connection state,
such as self.disconnected() or self.force_reconnect(), will also enable
a reconnect FSM."""
return self.state != Reconnect.Void
def enable(self, now):
"""If this FSM is disabled (the default for newly created FSMs),
enables it, so that the next call to reconnect_run() for 'fsm' will
return ovs.reconnect.CONNECT.
If this FSM is not disabled, this function has no effect."""
if self.state == Reconnect.Void and self.__may_retry():
self._transition(now, Reconnect.Backoff)
self.backoff = 0
def disable(self, now):
"""Disables this FSM. Until 'fsm' is enabled again, self.run() will
always return 0."""
if self.state != Reconnect.Void:
self._transition(now, Reconnect.Void)
def force_reconnect(self, now):
"""If this FSM is enabled and currently connected (or attempting to
connect), forces self.run() to return ovs.reconnect.DISCONNECT the next
time it is called, which should cause the client to drop the connection
(or attempt), back off, and then reconnect."""
if self.state in (Reconnect.ConnectInProgress,
Reconnect.Active,
Reconnect.Idle):
self._transition(now, Reconnect.Reconnect)
def disconnected(self, now, error):
"""Tell this FSM that the connection dropped or that a connection
attempt failed. 'error' specifies the reason: a positive value
represents an errno value, EOF indicates that the connection was closed
by the peer (e.g. read() returned 0), and 0 indicates no specific
error.
The FSM will back off, then reconnect."""
if self.state not in (Reconnect.Backoff, Reconnect.Void):
# Report what happened
if self.state in (Reconnect.Active, Reconnect.Idle):
if error > 0:
vlog.warn("%s: connection dropped (%s)"
% (self.name, os.strerror(error)))
elif error == EOF:
self.info_level("%s: connection closed by peer"
% self.name)
else:
self.info_level("%s: connection dropped" % self.name)
elif self.state == Reconnect.Listening:
if error > 0:
vlog.warn("%s: error listening for connections (%s)"
% (self.name, os.strerror(error)))
else:
self.info_level("%s: error listening for connections"
% self.name)
else:
if self.passive:
type_ = "listen"
else:
type_ = "connection"
if error > 0:
vlog.warn("%s: %s attempt failed (%s)"
% (self.name, type_, os.strerror(error)))
else:
self.info_level("%s: %s attempt timed out"
% (self.name, type_))
if (self.state in (Reconnect.Active, Reconnect.Idle)):
self.last_disconnected = now
# Back off
if (self.state in (Reconnect.Active, Reconnect.Idle) and
(self.last_activity - self.last_connected >= self.backoff or
self.passive)):
if self.passive:
self.backoff = 0
else:
self.backoff = self.min_backoff
else:
if self.backoff < self.min_backoff:
self.backoff = self.min_backoff
elif self.backoff >= self.max_backoff / 2:
self.backoff = self.max_backoff
else:
self.backoff *= 2
if self.passive:
self.info_level("%s: waiting %.3g seconds before trying "
"to listen again"
% (self.name, self.backoff / 1000.0))
else:
self.info_level("%s: waiting %.3g seconds before reconnect"
% (self.name, self.backoff / 1000.0))
if self.__may_retry():
self._transition(now, Reconnect.Backoff)
else:
self._transition(now, Reconnect.Void)
def connecting(self, now):
"""Tell this FSM that a connection or listening attempt is in progress.
The FSM will start a timer, after which the connection or listening
attempt will be aborted (by returning ovs.reconnect.DISCONNECT from
self.run())."""
if self.state != Reconnect.ConnectInProgress:
if self.passive:
self.info_level("%s: listening..." % self.name)
else:
self.info_level("%s: connecting..." % self.name)
self._transition(now, Reconnect.ConnectInProgress)
def listening(self, now):
"""Tell this FSM that the client is listening for connection attempts.
This state last indefinitely until the client reports some change.
The natural progression from this state is for the client to report
that a connection has been accepted or is in progress of being
accepted, by calling self.connecting() or self.connected().
The client may also report that listening failed (e.g. accept()
returned an unexpected error such as ENOMEM) by calling
self.listen_error(), in which case the FSM will back off and eventually
return ovs.reconnect.CONNECT from self.run() to tell the client to try
listening again."""
if self.state != Reconnect.Listening:
self.info_level("%s: listening..." % self.name)
self._transition(now, Reconnect.Listening)
def listen_error(self, now, error):
"""Tell this FSM that the client's attempt to accept a connection
failed (e.g. accept() returned an unexpected error such as ENOMEM).
If the FSM is currently listening (self.listening() was called), it
will back off and eventually return ovs.reconnect.CONNECT from
self.run() to tell the client to try listening again. If there is an
active connection, this will be delayed until that connection drops."""
if self.state == Reconnect.Listening:
self.disconnected(now, error)
def connected(self, now):
"""Tell this FSM that the connection was successful.
The FSM will start the probe interval timer, which is reset by
self.activity(). If the timer expires, a probe will be sent (by
returning ovs.reconnect.PROBE from self.run(). If the timer expires
again without being reset, the connection will be aborted (by returning
ovs.reconnect.DISCONNECT from self.run()."""
if not self.state.is_connected:
self.connecting(now)
self.info_level("%s: connected" % self.name)
self._transition(now, Reconnect.Active)
self.last_connected = now
def connect_failed(self, now, error):
"""Tell this FSM that the connection attempt failed.
The FSM will back off and attempt to reconnect."""
self.connecting(now)
self.disconnected(now, error)
def activity(self, now):
"""Tell this FSM that some activity occurred on the connection. This
resets the probe interval timer, so that the connection is known not to
be idle."""
if self.state != Reconnect.Active:
self._transition(now, Reconnect.Active)
self.last_activity = now
def _transition(self, now, state):
if self.state == Reconnect.ConnectInProgress:
self.n_attempted_connections += 1
if state == Reconnect.Active:
self.n_successful_connections += 1
connected_before = self.state.is_connected
connected_now = state.is_connected
if connected_before != connected_now:
if connected_before:
self.total_connected_duration += now - self.last_connected
self.seqno += 1
vlog.dbg("%s: entering %s" % (self.name, state.name))
self.state = state
self.state_entered = now
def run(self, now):
"""Assesses whether any action should be taken on this FSM. The return
value is one of:
- None: The client need not take any action.
- Active client, ovs.reconnect.CONNECT: The client should start a
connection attempt and indicate this by calling
self.connecting(). If the connection attempt has definitely
succeeded, it should call self.connected(). If the connection
attempt has definitely failed, it should call
self.connect_failed().
The FSM is smart enough to back off correctly after successful
connections that quickly abort, so it is OK to call
self.connected() after a low-level successful connection
(e.g. connect()) even if the connection might soon abort due to a
failure at a high-level (e.g. SSL negotiation failure).
- Passive client, ovs.reconnect.CONNECT: The client should try to
listen for a connection, if it is not already listening. It
should call self.listening() if successful, otherwise
self.connecting() or reconnected_connect_failed() if the attempt
is in progress or definitely failed, respectively.
A listening passive client should constantly attempt to accept a
new connection and report an accepted connection with
self.connected().
- ovs.reconnect.DISCONNECT: The client should abort the current
connection or connection attempt or listen attempt and call
self.disconnected() or self.connect_failed() to indicate it.
- ovs.reconnect.PROBE: The client should send some kind of request
to the peer that will elicit a response, to ensure that the
connection is indeed in working order. (This will only be
returned if the "probe interval" is nonzero--see
self.set_probe_interval())."""
deadline = self.state.deadline(self)
if deadline is not None and now >= deadline:
return self.state.run(self, now)
else:
return None
def wait(self, poller, now):
"""Causes the next call to poller.block() to wake up when self.run()
should be called."""
timeout = self.timeout(now)
if timeout >= 0:
poller.timer_wait(timeout)
def timeout(self, now):
"""Returns the number of milliseconds after which self.run() should be
called if nothing else notable happens in the meantime, or None if this
is currently unnecessary."""
deadline = self.state.deadline(self)
if deadline is not None:
remaining = deadline - now
return max(0, remaining)
else:
return None
def is_connected(self):
"""Returns True if this FSM is currently believed to be connected, that
is, if self.connected() was called more recently than any call to
self.connect_failed() or self.disconnected() or self.disable(), and
False otherwise."""
return self.state.is_connected
def get_last_connect_elapsed(self, now):
"""Returns the number of milliseconds since 'fsm' was last connected
to its peer. Returns None if never connected."""
if self.last_connected:
return now - self.last_connected
else:
return None
def get_last_disconnect_elapsed(self, now):
"""Returns the number of milliseconds since 'fsm' was last disconnected
from its peer. Returns None if never disconnected."""
if self.last_disconnected:
return now - self.last_disconnected
else:
return None
def get_stats(self, now):
class Stats(object):
pass
stats = Stats()
stats.creation_time = self.creation_time
stats.last_connected = self.last_connected
stats.last_disconnected = self.last_disconnected
stats.last_activity = self.last_activity
stats.backoff = self.backoff
stats.seqno = self.seqno
stats.is_connected = self.is_connected()
stats.msec_since_connect = self.get_last_connect_elapsed(now)
stats.msec_since_disconnect = self.get_last_disconnect_elapsed(now)
stats.total_connected_duration = self.total_connected_duration
if self.is_connected():
stats.total_connected_duration += (
self.get_last_connect_elapsed(now))
stats.n_attempted_connections = self.n_attempted_connections
stats.n_successful_connections = self.n_successful_connections
stats.state = self.state.name
stats.state_elapsed = now - self.state_entered
return stats
def __may_retry(self):
if self.max_tries is None:
return True
elif self.max_tries > 0:
self.max_tries -= 1
return True
else:
return False
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