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"""A basic kernel monitor with autorestarting.
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This watches a kernel's state using KernelManager.is_alive and auto
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restarts the kernel if it dies.
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It is an incomplete base class, and must be subclassed.
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"""
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# Copyright (c) IPython Development Team.
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# Distributed under the terms of the Modified BSD License.
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from IPython.config.configurable import LoggingConfigurable
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from IPython.utils.traitlets import (
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Instance, Float, Dict, Bool, Integer,
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)
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class KernelRestarter(LoggingConfigurable):
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"""Monitor and autorestart a kernel."""
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kernel_manager = Instance('IPython.kernel.KernelManager')
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debug = Bool(False, config=True,
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help="""Whether to include every poll event in debugging output.
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Has to be set explicitly, because there will be *a lot* of output.
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"""
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)
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time_to_dead = Float(3.0, config=True,
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help="""Kernel heartbeat interval in seconds."""
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)
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restart_limit = Integer(5, config=True,
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help="""The number of consecutive autorestarts before the kernel is presumed dead."""
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)
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_restarting = Bool(False)
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_restart_count = Integer(0)
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callbacks = Dict()
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def _callbacks_default(self):
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return dict(restart=[], dead=[])
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def start(self):
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"""Start the polling of the kernel."""
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raise NotImplementedError("Must be implemented in a subclass")
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def stop(self):
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"""Stop the kernel polling."""
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raise NotImplementedError("Must be implemented in a subclass")
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def add_callback(self, f, event='restart'):
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"""register a callback to fire on a particular event
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Possible values for event:
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'restart' (default): kernel has died, and will be restarted.
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'dead': restart has failed, kernel will be left dead.
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"""
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self.callbacks[event].append(f)
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def remove_callback(self, f, event='restart'):
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"""unregister a callback to fire on a particular event
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Possible values for event:
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'restart' (default): kernel has died, and will be restarted.
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'dead': restart has failed, kernel will be left dead.
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"""
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try:
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self.callbacks[event].remove(f)
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except ValueError:
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pass
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def _fire_callbacks(self, event):
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"""fire our callbacks for a particular event"""
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for callback in self.callbacks[event]:
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try:
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callback()
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except Exception as e:
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self.log.error("KernelRestarter: %s callback %r failed", event, callback, exc_info=True)
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def poll(self):
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if self.debug:
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self.log.debug('Polling kernel...')
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if not self.kernel_manager.is_alive():
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if self._restarting:
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self._restart_count += 1
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else:
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self._restart_count = 1
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if self._restart_count >= self.restart_limit:
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self.log.warn("KernelRestarter: restart failed")
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self._fire_callbacks('dead')
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self._restarting = False
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self._restart_count = 0
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self.stop()
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else:
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self.log.info('KernelRestarter: restarting kernel (%i/%i)',
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self._restart_count,
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self.restart_limit
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)
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self._fire_callbacks('restart')
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self.kernel_manager.restart_kernel(now=True)
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self._restarting = True
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else:
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if self._restarting:
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self.log.debug("KernelRestarter: restart apparently succeeded")
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self._restarting = False
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