Source code for google.appengine.ext.ndb.eventloop

# Copyright 2008 The ndb Authors. All Rights Reserved.
# 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
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.

"""An event loop.

This event loop should handle both asynchronous App Engine RPC objects
(specifically urlfetch, memcache and datastore RPC objects) and arbitrary
callback functions with an optional time delay.

Normally, event loops are singleton objects, though there is no
enforcement of this requirement.

The API here is inspired by Monocle.

import collections
import logging
import os
import time

from .google_imports import apiproxy_rpc
from .google_imports import datastore_rpc

from . import utils

__all__ = ['EventLoop',
           'add_idle', 'queue_call', 'queue_rpc',
           'run', 'run0', 'run1',

_logging_debug = utils.logging_debug

_IDLE = apiproxy_rpc.RPC.IDLE
_RUNNING = apiproxy_rpc.RPC.RUNNING

class _Clock(object):
  """A clock to determine the current time, in seconds."""

  def now(self):
    """Returns the number of seconds since epoch."""
    return time.time()

  def sleep(self, seconds):
    """Sleeps for the desired number of seconds."""

[docs]class EventLoop(object): """An event loop.""" def __init__(self, clock=None): """Constructor. Args: clock: an eventloop._Clock object. Defaults to a time-based clock. Fields: current: a FIFO list of (callback, args, kwds). These callbacks run immediately when the eventloop runs. idlers: a FIFO list of (callback, args, kwds). Thes callbacks run only when no other RPCs need to be fired first. For example, AutoBatcher uses idler to fire a batch RPC even before the batch is full. queue: a sorted list of (absolute time in sec, callback, args, kwds), sorted by time. These callbacks run only after the said time. rpcs: a map from rpc to (callback, args, kwds). Callback is called when the rpc finishes. """ self.clock = clock or _Clock() self.current = collections.deque() self.idlers = collections.deque() self.inactive = 0 # How many idlers in a row were no-ops self.queue = [] self.rpcs = {}
[docs] def clear(self): """Remove all pending events without running any.""" while self.current or self.idlers or self.queue or self.rpcs: current = self.current idlers = self.idlers queue = self.queue rpcs = self.rpcs _logging_debug('Clearing stale EventLoop instance...') if current: _logging_debug(' current = %s', current) if idlers: _logging_debug(' idlers = %s', idlers) if queue: _logging_debug(' queue = %s', queue) if rpcs: _logging_debug(' rpcs = %s', rpcs) self.__init__() current.clear() idlers.clear() queue[:] = [] rpcs.clear() _logging_debug('Cleared')
[docs] def insort_event_right(self, event, lo=0, hi=None): """Insert event in queue, and keep it sorted assuming queue is sorted. If event is already in queue, insert it to the right of the rightmost event (to keep FIFO order). Optional args lo (default 0) and hi (default len(a)) bound the slice of a to be searched. Args: event: a (time in sec since unix epoch, callback, args, kwds) tuple. """ if lo < 0: raise ValueError('lo must be non-negative') if hi is None: hi = len(self.queue) while lo < hi: mid = (lo + hi) // 2 if event[0] < self.queue[mid][0]: hi = mid else: lo = mid + 1 self.queue.insert(lo, event)
[docs] def queue_call(self, delay, callback, *args, **kwds): """Schedule a function call at a specific time in the future.""" if delay is None: self.current.append((callback, args, kwds)) return if delay < 1e9: when = delay + else: # Times over a billion seconds are assumed to be absolute. when = delay self.insort_event_right((when, callback, args, kwds))
[docs] def queue_rpc(self, rpc, callback=None, *args, **kwds): """Schedule an RPC with an optional callback. The caller must have previously sent the call to the service. The optional callback is called with the remaining arguments. NOTE: If the rpc is a MultiRpc, the callback will be called once for each sub-RPC. TODO: Is this a good idea? """ if rpc is None: return if rpc.state not in (_RUNNING, _FINISHING): raise RuntimeError('rpc must be sent to service before queueing') if isinstance(rpc, datastore_rpc.MultiRpc): rpcs = rpc.rpcs if len(rpcs) > 1: # Don't call the callback until all sub-rpcs have completed. rpc.__done = False def help_multi_rpc_along(r=rpc, c=callback, a=args, k=kwds): if r.state == _FINISHING and not r.__done: r.__done = True c(*a, **k) # TODO: And again, what about exceptions? callback = help_multi_rpc_along args = () kwds = {} else: rpcs = [rpc] for rpc in rpcs: self.rpcs[rpc] = (callback, args, kwds)
[docs] def add_idle(self, callback, *args, **kwds): """Add an idle callback. An idle callback can return True, False or None. These mean: - None: remove the callback (don't reschedule) - False: the callback did no work; reschedule later - True: the callback did some work; reschedule soon If the callback raises an exception, the traceback is logged and the callback is removed. """ self.idlers.append((callback, args, kwds))
[docs] def run_idle(self): """Run one of the idle callbacks. Returns: True if one was called, False if no idle callback was called. """ if not self.idlers or self.inactive >= len(self.idlers): return False idler = self.idlers.popleft() callback, args, kwds = idler _logging_debug('idler: %s', callback.__name__) res = callback(*args, **kwds) # See add_idle() for the meaning of the callback return value. if res is not None: if res: self.inactive = 0 else: self.inactive += 1 self.idlers.append(idler) else: _logging_debug('idler %s removed', callback.__name__) return True
[docs] def run0(self): """Run one item (a callback or an RPC wait_any). Returns: A time to sleep if something happened (may be 0); None if all queues are empty. """ if self.current: self.inactive = 0 callback, args, kwds = self.current.popleft() _logging_debug('nowevent: %s', callback.__name__) callback(*args, **kwds) return 0 if self.run_idle(): return 0 delay = None if self.queue: delay = self.queue[0][0] - if delay <= 0: self.inactive = 0 _, callback, args, kwds = self.queue.pop(0) _logging_debug('event: %s', callback.__name__) callback(*args, **kwds) # TODO: What if it raises an exception? return 0 if self.rpcs: self.inactive = 0 rpc = datastore_rpc.MultiRpc.wait_any(self.rpcs) if rpc is not None: _logging_debug('rpc: %s.%s', rpc.service, rpc.method) # Yes, wait_any() may return None even for a non-empty argument. # But no, it won't ever return an RPC not in its argument. if rpc not in self.rpcs: raise RuntimeError('rpc %r was not given to wait_any as a choice %r' % (rpc, self.rpcs)) callback, args, kwds = self.rpcs[rpc] del self.rpcs[rpc] if callback is not None: callback(*args, **kwds) # TODO: Again, what about exceptions? return 0 return delay
[docs] def run1(self): """Run one item (a callback or an RPC wait_any) or sleep. Returns: True if something happened; False if all queues are empty. """ delay = self.run0() if delay is None: return False if delay > 0: self.clock.sleep(delay) return True
[docs] def run(self): """Run until there's nothing left to do.""" # TODO: A way to stop running before the queue is empty. self.inactive = 0 while True: if not self.run1(): break
class _State(utils.threading_local): event_loop = None _EVENT_LOOP_KEY = '__EVENT_LOOP__' _state = _State()
[docs]def get_event_loop(): """Return a EventLoop instance. A new instance is created for each new HTTP request. We determine that we're in a new request by inspecting os.environ, which is reset at the start of each request. Also, each thread gets its own loop. """ ev = _state.event_loop if not os.getenv(_EVENT_LOOP_KEY) and ev is not None: ev.clear() _state.event_loop = None ev = None if ev is None: ev = EventLoop() _state.event_loop = ev os.environ[_EVENT_LOOP_KEY] = '1' return ev
[docs]def queue_call(*args, **kwds): ev = get_event_loop() ev.queue_call(*args, **kwds)
[docs]def queue_rpc(rpc, callback=None, *args, **kwds): ev = get_event_loop() ev.queue_rpc(rpc, callback, *args, **kwds)
[docs]def add_idle(callback, *args, **kwds): ev = get_event_loop() ev.add_idle(callback, *args, **kwds)
[docs]def run(): ev = get_event_loop()
[docs]def run1(): ev = get_event_loop() return ev.run1()
[docs]def run0(): ev = get_event_loop() return ev.run0()

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