text: import logging
  
  logger = logging.getLogger(__name__)
  
  
  class SchedulerPlugin:
      """Interface to extend the Scheduler
  
      The scheduler operates by triggering and responding to events like
      ``task_finished``, ``update_graph``, ``task_erred``, etc..
  
      A plugin enables custom code to run at each of those same events.  The
      scheduler will run the analogous methods on this class when each event is
      triggered.  This runs user code within the scheduler thread that can
      perform arbitrary operations in synchrony with the scheduler itself.
  
      Plugins are often used for diagnostics and measurement, but have full
      access to the scheduler and could in principle affect core scheduling.
  
      To implement a plugin implement some of the methods of this class and add
      the plugin to the scheduler with ``Scheduler.add_plugin(myplugin)``.
  
      Examples
      --------
      >>> class Counter(SchedulerPlugin):
      ...     def __init__(self):
      ...         self.counter = 0
      ...
      ...     def transition(self, key, start, finish, *args, **kwargs):
      ...         if start == 'processing' and finish == 'memory':
      ...             self.counter += 1
      ...
      ...     def restart(self, scheduler):
      ...         self.counter = 0
  
      >>> plugin = Counter()
      >>> scheduler.add_plugin(plugin)  # doctest: +SKIP
      """
  
      async def start(self, scheduler):
          """Run when the scheduler starts up
  
          This runs at the end of the Scheduler startup process
          """
          pass
  
      async def close(self):
          """Run when the scheduler closes down
  
          This runs at the beginning of the Scheduler shutdown process, but after
          workers have been asked to shut down gracefully
          """
          pass
  
      def update_graph(self, scheduler, dsk=None, keys=None, restrictions=None, **kwargs):
          """ Run when a new graph / tasks enter the scheduler """
  
      def restart(self, scheduler, **kwargs):
          """ Run when the scheduler restarts itself """
  
      def transition(self, key, start, finish, *args, **kwargs):
          """Run whenever a task changes state
  
          Parameters
          ----------
          key: string
          start: string
              Start state of the transition.
              One of released, waiting, processing, memory, error.
          finish: string
              Final state of the transition.
          *args, **kwargs: More options passed when transitioning
              This may include worker ID, compute time, etc.
          """
  
      def add_worker(self, scheduler=None, worker=None, **kwargs):
          """ Run when a new worker enters the cluster """
  
      def remove_worker(self, scheduler=None, worker=None, **kwargs):
          """ Run when a worker leaves the cluster """
  
      def add_client(self, scheduler=None, client=None, **kwargs):
          """ Run when a new client connects """
  
      def remove_client(self, scheduler=None, client=None, **kwargs):
          """ Run when a client disconnects """
  
  
  class WorkerPlugin:
      """Interface to extend the Worker
  
      A worker plugin enables custom code to run at different stages of the Workers'
      lifecycle: at setup, during task state transitions, when a task or dependency
      is released, and at teardown.
  
      A plugin enables custom code to run at each of step of a Workers's life. Whenever such
      an event happens, the corresponding method on this class will be called. Note that the
      user code always runs within the Worker's main thread.
  
      To implement a plugin implement some of the methods of this class and register
      the plugin to your client in order to have it attached to every existing and
      future workers with ``Client.register_worker_plugin``.
  
      Examples
      --------
      >>> class ErrorLogger(WorkerPlugin):
      ...     def __init__(self, logger):
      ...         self.logger = logger
      ...
      ...     def setup(self, worker):
      ...         self.worker = worker
      ...
      ...     def transition(self, key, start, finish, *args, **kwargs):
      ...         if finish == 'error':
      ...             exc = self.worker.exceptions[key]
      ...             self.logger.error("Task '%s' has failed with exception: %s" % (key, str(exc)))
  
      >>> plugin = ErrorLogger()
      >>> client.register_worker_plugin(plugin)  # doctest: +SKIP
      """
  
      def setup(self, worker):
          """
          Run when the plugin is attached to a worker. This happens when the plugin is registered
          and attached to existing workers, or when a worker is created after the plugin has been
          registered.
          """
  
      def teardown(self, worker):
          """ Run when the worker to which the plugin is attached to is closed """
  
      def transition(self, key, start, finish, **kwargs):
          """
          Throughout the lifecycle of a task (see :doc:`Worker <worker>`), Workers are
          instructed by the scheduler to compute certain tasks, resulting in transitions
          in the state of each task. The Worker owning the task is then notified of this
          state transition.
  
          Whenever a task changes its state, this method will be called.
  
          Parameters
          ----------
          key: string
          start: string
              Start state of the transition.
              One of waiting, ready, executing, long-running, memory, error.
          finish: string
              Final state of the transition.
          kwargs: More options passed when transitioning
          """
  
      def release_key(self, key, state, cause, reason, report):
          """
          Called when the worker releases a task.
  
          Parameters
          ----------
          key: string
          state: string
              State of the released task.
              One of waiting, ready, executing, long-running, memory, error.
          cause: string or None
              Additional information on what triggered the release of the task.
          reason: None
              Not used.
          report: bool
              Whether the worker should report the released task to the scheduler.
          """
  
      def release_dep(self, dep, state, report):
          """
          Called when the worker releases a dependency.
  
          Parameters
          ----------
          dep: string
          state: string
              State of the released dependency.
              One of waiting, flight, memory.
          report: bool
              Whether the worker should report the released dependency to the scheduler.
          """
  