tahoe-lafs/src/allmydata/monitor.py
2008-10-21 17:52:56 -07:00

103 lines
3.8 KiB
Python

from zope.interface import Interface, implements
from allmydata.util import observer
class IMonitor(Interface):
"""I manage status, progress, and cancellation for long-running operations.
Whoever initiates the operation should create a Monitor instance and pass
it into the code that implements the operation. That code should
periodically check in with the Monitor, perhaps after each major unit of
work has been completed, for two purposes.
The first is to inform the Monitor about progress that has been made, so
that external observers can be reassured that the operation is proceeding
normally. If the operation has a well-known amount of work to perform,
this notification should reflect that, so that an ETA or 'percentage
complete' value can be derived.
The second purpose is to check to see if the operation has been
cancelled. The impatient observer who no longer wants the operation to
continue will inform the Monitor; the next time the operation code checks
in, it should notice that the operation has been cancelled, and wrap
things up. The same monitor can be passed to multiple operations, all of
which may check for cancellation: this pattern may be simpler than having
the original caller keep track of subtasks and cancel them individually.
"""
# the following methods are provided for the operation code
def is_cancelled(self):
"""Returns True if the operation has been cancelled. If True,
operation code should stop creating new work, and attempt to stop any
work already in progress."""
def set_status(self, status):
"""Sets the Monitor's 'status' object to an arbitrary value.
Different operations will store different sorts of status information
here. Operation code should use get+modify+set sequences to update
this."""
def get_status(self):
"""Return the status object."""
def finish(self, status):
"""Call this when the operation is done, successful or not. The
Monitor's lifetime is influenced by the completion of the operation
it is monitoring. The Monitor's 'status' value will be set with the
'status' argument, just as if it had been passed to set_status().
This value will be used to fire the Deferreds that are returned by
when_done().
Operations that fire a Deferred when they finish should trigger this
with d.addBoth(monitor.finish)"""
# the following methods are provided for the initiator of the operation
def is_finished(self):
"""Return a boolean, True if the operation is done (whether
successful or failed), False if it is still running."""
def when_done(self):
"""Return a Deferred that fires when the operation is complete. It
will fire with the operation status, the same value as returned by
get_status()."""
def cancel(self):
"""Cancel the operation as soon as possible. is_cancelled() will
start returning True after this is called."""
# get_status() is useful too, but it is operation-specific
class Monitor:
implements(IMonitor)
def __init__(self):
self.cancelled = False
self.finished = False
self.status = None
self.observer = observer.OneShotObserverList()
def is_cancelled(self):
return self.cancelled
def is_finished(self):
return self.finished
def when_done(self):
return self.observer.when_fired()
def cancel(self):
self.cancelled = True
def finish(self, status_or_failure):
self.set_status(status_or_failure)
self.finished = True
self.observer.fire(status_or_failure)
return status_or_failure
def get_status(self):
return self.status
def set_status(self, status):
self.status = status