diff options
Diffstat (limited to 'synapse/util/async.py')
| -rw-r--r-- | synapse/util/async.py | 151 |
1 files changed, 130 insertions, 21 deletions
diff --git a/synapse/util/async.py b/synapse/util/async.py index 35380bf8ed..9dd4e6b5bc 100644 --- a/synapse/util/async.py +++ b/synapse/util/async.py @@ -15,16 +15,20 @@ from twisted.internet import defer, reactor +from twisted.internet.defer import CancelledError +from twisted.python import failure from .logcontext import ( - PreserveLoggingContext, preserve_fn, preserve_context_over_deferred, + PreserveLoggingContext, make_deferred_yieldable, run_in_background ) -from synapse.util import unwrapFirstError +from synapse.util import logcontext, unwrapFirstError from contextlib import contextmanager import logging +from six.moves import range + logger = logging.getLogger(__name__) @@ -53,6 +57,11 @@ class ObservableDeferred(object): Cancelling or otherwise resolving an observer will not affect the original ObservableDeferred. + + NB that it does not attempt to do anything with logcontexts; in general + you should probably make_deferred_yieldable the deferreds + returned by `observe`, and ensure that the original deferred runs its + callbacks in the sentinel logcontext. """ __slots__ = ["_deferred", "_observers", "_result"] @@ -68,7 +77,7 @@ class ObservableDeferred(object): try: # TODO: Handle errors here. self._observers.pop().callback(r) - except: + except Exception: pass return r @@ -78,7 +87,7 @@ class ObservableDeferred(object): try: # TODO: Handle errors here. self._observers.pop().errback(f) - except: + except Exception: pass if consumeErrors: @@ -89,6 +98,11 @@ class ObservableDeferred(object): deferred.addCallbacks(callback, errback) def observe(self): + """Observe the underlying deferred. + + Can return either a deferred if the underlying deferred is still pending + (or has failed), or the actual value. Callers may need to use maybeDeferred. + """ if not self._result: d = defer.Deferred() @@ -101,7 +115,7 @@ class ObservableDeferred(object): return d else: success, res = self._result - return defer.succeed(res) if success else defer.fail(res) + return res if success else defer.fail(res) def observers(self): return self._observers @@ -146,13 +160,13 @@ def concurrently_execute(func, args, limit): def _concurrently_execute_inner(): try: while True: - yield func(it.next()) + yield func(next(it)) except StopIteration: pass - return preserve_context_over_deferred(defer.gatherResults([ - preserve_fn(_concurrently_execute_inner)() - for _ in xrange(limit) + return logcontext.make_deferred_yieldable(defer.gatherResults([ + run_in_background(_concurrently_execute_inner) + for _ in range(limit) ], consumeErrors=True)).addErrback(unwrapFirstError) @@ -195,10 +209,29 @@ class Linearizer(object): try: with PreserveLoggingContext(): yield current_defer - except: + except Exception: logger.exception("Unexpected exception in Linearizer") - logger.info("Acquired linearizer lock %r for key %r", self.name, key) + logger.info("Acquired linearizer lock %r for key %r", self.name, + key) + + # if the code holding the lock completes synchronously, then it + # will recursively run the next claimant on the list. That can + # relatively rapidly lead to stack exhaustion. This is essentially + # the same problem as http://twistedmatrix.com/trac/ticket/9304. + # + # In order to break the cycle, we add a cheeky sleep(0) here to + # ensure that we fall back to the reactor between each iteration. + # + # (There's no particular need for it to happen before we return + # the context manager, but it needs to happen while we hold the + # lock, and the context manager's exit code must be synchronous, + # so actually this is the only sensible place. + yield run_on_reactor() + + else: + logger.info("Acquired uncontended linearizer lock %r for key %r", + self.name, key) @contextmanager def _ctx_manager(): @@ -206,7 +239,8 @@ class Linearizer(object): yield finally: logger.info("Releasing linearizer lock %r for key %r", self.name, key) - new_defer.callback(None) + with PreserveLoggingContext(): + new_defer.callback(None) current_d = self.key_to_defer.get(key) if current_d is new_defer: self.key_to_defer.pop(key, None) @@ -248,8 +282,13 @@ class Limiter(object): if entry[0] >= self.max_count: new_defer = defer.Deferred() entry[1].append(new_defer) + + logger.info("Waiting to acquire limiter lock for key %r", key) with PreserveLoggingContext(): yield new_defer + logger.info("Acquired limiter lock for key %r", key) + else: + logger.info("Acquired uncontended limiter lock for key %r", key) entry[0] += 1 @@ -258,16 +297,21 @@ class Limiter(object): try: yield finally: + logger.info("Releasing limiter lock for key %r", key) + # We've finished executing so check if there are any things # blocked waiting to execute and start one of them entry[0] -= 1 - try: - entry[1].pop(0).callback(None) - except IndexError: - # If nothing else is executing for this key then remove it - # from the map - if entry[0] == 0: - self.key_to_defer.pop(key, None) + + if entry[1]: + next_def = entry[1].pop(0) + + with PreserveLoggingContext(): + next_def.callback(None) + elif entry[0] == 0: + # We were the last thing for this key: remove it from the + # map. + del self.key_to_defer[key] defer.returnValue(_ctx_manager()) @@ -311,7 +355,7 @@ class ReadWriteLock(object): # We wait for the latest writer to finish writing. We can safely ignore # any existing readers... as they're readers. - yield curr_writer + yield make_deferred_yieldable(curr_writer) @contextmanager def _ctx_manager(): @@ -340,7 +384,7 @@ class ReadWriteLock(object): curr_readers.clear() self.key_to_current_writer[key] = new_defer - yield preserve_context_over_deferred(defer.gatherResults(to_wait_on)) + yield make_deferred_yieldable(defer.gatherResults(to_wait_on)) @contextmanager def _ctx_manager(): @@ -352,3 +396,68 @@ class ReadWriteLock(object): self.key_to_current_writer.pop(key) defer.returnValue(_ctx_manager()) + + +class DeferredTimeoutError(Exception): + """ + This error is raised by default when a L{Deferred} times out. + """ + + +def add_timeout_to_deferred(deferred, timeout, on_timeout_cancel=None): + """ + Add a timeout to a deferred by scheduling it to be cancelled after + timeout seconds. + + This is essentially a backport of deferred.addTimeout, which was introduced + in twisted 16.5. + + If the deferred gets timed out, it errbacks with a DeferredTimeoutError, + unless a cancelable function was passed to its initialization or unless + a different on_timeout_cancel callable is provided. + + Args: + deferred (defer.Deferred): deferred to be timed out + timeout (Number): seconds to time out after + + on_timeout_cancel (callable): A callable which is called immediately + after the deferred times out, and not if this deferred is + otherwise cancelled before the timeout. + + It takes an arbitrary value, which is the value of the deferred at + that exact point in time (probably a CancelledError Failure), and + the timeout. + + The default callable (if none is provided) will translate a + CancelledError Failure into a DeferredTimeoutError. + """ + timed_out = [False] + + def time_it_out(): + timed_out[0] = True + deferred.cancel() + + delayed_call = reactor.callLater(timeout, time_it_out) + + def convert_cancelled(value): + if timed_out[0]: + to_call = on_timeout_cancel or _cancelled_to_timed_out_error + return to_call(value, timeout) + return value + + deferred.addBoth(convert_cancelled) + + def cancel_timeout(result): + # stop the pending call to cancel the deferred if it's been fired + if delayed_call.active(): + delayed_call.cancel() + return result + + deferred.addBoth(cancel_timeout) + + +def _cancelled_to_timed_out_error(value, timeout): + if isinstance(value, failure.Failure): + value.trap(CancelledError) + raise DeferredTimeoutError(timeout, "Deferred") + return value |