Source code for

# -*- coding: utf-8 -*-
This module contains the Girder events framework. It maintains a global mapping
of events to listeners, and contains utilities for callers to handle or trigger
events identified by a name.

Listeners should bind to events by calling:

    ``'', 'my.handler', handlerFunction)``

And events should be fired in one of two ways; if the event should be handled
synchronously, fire it with:

    ``'', info)``

And if the event should be handled asynchronously, use:

    ``'', info, callback)``

For obvious reasons, the asynchronous method does not return a value to the
caller. Instead, the caller may optionally pass the callback argument as a
function to be called when the task is finished. That callback function will
receive the Event object as its only argument.

import contextlib
import girder
import queue
import threading

from collections import OrderedDict
from girder.utility import config

[docs]class Event: """ An Event object is created when an event is triggered. It is passed to each of the listeners of the event, which have a chance to add information to the event, and also optionally stop the event from being further propagated to other listeners, and also optionally instruct the caller that it should not execute its default behavior. """ # We might have a lot of events, so we use __slots__ to make them smaller __slots__ = ( 'asynchronous', 'info', 'name', 'propagate', 'defaultPrevented', 'responses', 'currentHandlerName' ) def __init__(self, name, info, asynchronous=False): = name = info self.propagate = True self.defaultPrevented = False self.responses = [] self.currentHandlerName = None self.asynchronous = asynchronous
[docs] def preventDefault(self): """ This can be used to instruct the triggerer of the event that the default behavior it would normally perform should not be performed. The semantics of this action are specific to the context of the event being handled, but a common use of this method is for a plugin to provide an alternate behavior that will replace the normal way the event is handled by the core system. """ self.defaultPrevented = True return self
[docs] def stopPropagation(self): """ Listeners should call this on the event they were passed in order to stop any other listeners to the event from being executed. """ self.propagate = False return self
[docs] def addResponse(self, response): """ Listeners that wish to return data back to the caller who triggered this event should call this to append their own response to the event. :param response: The response value, which can be any type. """ self.responses.append(response) return self
[docs]class ForegroundEventsDaemon: """ This is the implementation used for ```` if the config file chooses to disable using the background thread for the daemon. It executes all bound handlers in the current thread, and provides no-op start() and stop() implementations to remain compatible with the API of AsyncEventsThread. """ def start(self): pass def stop(self): pass def trigger(self, eventName=None, info=None, callback=None): if eventName is None: event = Event(None, info, asynchronous=False) else: event = trigger(eventName, info, asynchronous=False, daemon=True) if callable(callback): callback(event)
[docs]class AsyncEventsThread(threading.Thread): """ This class is used to execute the pipeline for events asynchronously. This should not be invoked directly by callers; instead, they should use """ def __init__(self): super().__init__() self.daemon = True self.terminate = False self.eventQueue = queue.Queue() self.queueNotEmpty = threading.Condition()
[docs] def run(self): """ Loops over all queued events. If the queue is empty, this thread gets put to sleep until someone calls trigger() on it with a new event to dispatch. """'Started asynchronous event manager thread.') while not self.terminate: try: eventName, info, callback = self.eventQueue.get(block=False) if eventName is None: event = Event(None, info, asynchronous=True) else: event = trigger(eventName, info, asynchronous=True, daemon=True) if callable(callback): callback(event) except queue.Empty: self.queueNotEmpty.acquire() self.queueNotEmpty.wait() self.queueNotEmpty.release() except Exception: # Must continue the event loop even if handler failed girder.logger.exception('In handler for event "%s":' % eventName)'Stopped asynchronous event manager thread.')
[docs] def trigger(self, eventName=None, info=None, callback=None): """ Adds a new event on the queue to trigger asynchronously. :param eventName: The event name to pass to the :param info: The info object to pass to :param callback: Optional callable to be called upon completion of all bound event handlers. It takes one argument, which is the event object itself. """ self.queueNotEmpty.acquire() self.eventQueue.put((eventName, info, callback)) self.queueNotEmpty.notify() self.queueNotEmpty.release()
[docs] def stop(self): """ Gracefully stops this thread. Will finish the currently processing event before stopping. """ self.queueNotEmpty.acquire() self.terminate = True self.queueNotEmpty.notify() self.queueNotEmpty.release()
def __del__(self): # Make sure we stop this thread if it's getting GCed, i.e. daemon was reassigned self.stop()
# We had been calling the super class's __del__, but it doesn't have # such a method, so doing so would raise an AttributeError. # super().__del__()
[docs]def bind(eventName, handlerName, handler): """ Bind a listener (handler) to the event identified by eventName. It is convention that plugins will use their own name as the handlerName, so that the trigger() caller can see which plugin(s) responded to the event. :param eventName: The name that identifies the event. :type eventName: str :param handlerName: The name that identifies the handler calling bind(). :type handlerName: str :param handler: The function that will be called when the event is fired. It must accept a single argument, which is the Event that was created by trigger(). This function should not return a value; any data that it needs to pass back to the triggerer should be passed via the addResponse() method of the Event. :type handler: function """ if eventName in _deprecated: girder.logger.warning('event "%s" is deprecated; %s' % (eventName, _deprecated[eventName])) if eventName not in _mapping: _mapping[eventName] = OrderedDict() if handlerName in _mapping[eventName]: girder.logger.warning('Event binding already exists: %s -> %s' % (eventName, handlerName)) _mapping[eventName][handlerName] = handler
[docs]def unbind(eventName, handlerName): """ Removes the binding between the event and the given listener. :param eventName: The name that identifies the event. :type eventName: str :param handlerName: The name that identifies the handler calling bind(). :type handlerName: str """ _mapping.get(eventName, {}).pop(handlerName, None)
[docs]def unbindAll(): """ Clears the entire event map. All bound listeners will be unbound. .. warning:: This will also disable internal event listeners, which are necessary for normal Girder functionality. This function should generally never be called outside of testing. """ _mapping.clear()
[docs]@contextlib.contextmanager def bound(eventName, handlerName, handler): """ A context manager to temporarily bind an event handler within its scope. Parameters are the same as those to :py:func:``. """ bind(eventName, handlerName, handler) try: yield finally: unbind(eventName, handlerName)
[docs]def trigger(eventName, info=None, pre=None, asynchronous=False, daemon=False): """ Fire an event with the given name. All listeners bound on that name will be called until they are exhausted or one of the handlers calls the stopPropagation() method on the event. :param eventName: The name that identifies the event. :type eventName: str :param info: The info argument to pass to the handler function. The type of this argument is opaque, and can be anything. :param pre: A function that will be executed prior to the handler being executed. It will receive a dict with a "handler" key, (the function), "info" key (the info arg to this function), and "eventName" and "handlerName" values. :type pre: function or None :param asynchronous: Whether this event is executing on the background thread (True) or on the request thread (False). :type asynchronous: bool :param daemon: Whether this was triggered via ````. :type daemon: bool """ e = Event(eventName, info, asynchronous=asynchronous) for name, handler in _mapping.get(eventName, {}).items(): if daemon and not asynchronous: girder.logprint.warning( 'WARNING: Handler "%s" for event "%s" was triggered on the daemon, but is ' 'actually running synchronously.' % (name, eventName)) e.currentHandlerName = name if pre is not None: pre(info=info, handler=handler, eventName=eventName, handlerName=name) handler(e) if e.propagate is False: break return e
_deprecated = {} _mapping = {} daemon = ForegroundEventsDaemon() def setupDaemon(): global daemon if config.getConfig()['server'].get('disable_event_daemon', False): daemon = ForegroundEventsDaemon() else: daemon = AsyncEventsThread()