mirror of
https://github.com/dart-lang/sdk
synced 2024-09-16 01:21:07 +00:00
69f32d6ad7
This is a major rewrite of the `_Future` class, which is the default implementation of the `Future` interface. The main goal was to reduce the number of expensive type checks in the internal passing around of data. Expensive type checks are things like * `is _Future<T>` (more expensive than just `is _Future`, the latter can be a single class-ID check. * Covariant generic parameter checks (using `T` covariantly in a parameter forces a run-time type check). Also removed some plain unnecessary casts and turned some implicit casts from `dynamic` into `unsafeCast`s. This seems to be an success, at least on very primitive benchmarks, according to Golem: FutureCatchErrorTest 41.22% (1.9 noise) FutureValueTest 46.51% (2.8 noise) EmptyFutureTest 59.15% (3.1 noise) FutureWhenCompleteTest 51.10% (3.2 noise) A secondary goal was to clean up a very old and messy class, and make it clearer for other `dart:async` how to interact with the future. The change has a memory cost: The `_FutureListener<S,T>` class, which represents a `then`, `catchError` or `whenComplete` call on a `_Future`, now contains a reference to its source future, the one which provides the inputs to the callbacks, as well as the result future returned by the call. That's one extra memory slot per listener. In return, the `_FutureListener` now does not need to get its source future as an argument, which needs a covariant generic type check, and the methods of `_Future` can be written in a way which ignores the type parameters of both `_Future` and `_FutureListener`, which reduces complex type checks significantly. In general, typed code is in `_FutureListener`, which knows both the source and target types of the listener callbacks, and which contains the futures already at that type, so no extra type checking is needed. The `_Future` class is mostly untyped, except for its "public" API, called by other classes, which checks inputs, and code interacting with non-native futures. Invariants ensure that only correctly typed values are stored in the untyped shared `_resultOrListeners` field on `_Future`, as determined by its `_state` integer. (This was already partially true, and has simply been made more consistent.) Further, we now throw an error in a situation that was previously unhandled: When a `_Future` is completed with *itself*. That would ensure that the future would never complete (it waits for itself to complete before it can complete), and may potentially have caused weird loops in the representation. In practice, it probably never happens. Now it makes the error fail with an error. Currently a private `_FutureCyclicDependencyError` which presents as an `UnsupportedError`. That avoids code like ```dart import "dart:async"; void main() { var c = Completer(); c.complete(c.future); // bad. print("well!"); var d = Completer(); d.complete(c.future); print("shucks!"); } ``` from hanging the runtime by busily searching for the end of a cycle. See https://github.com/dart-lang/sdk/issues/48225 Fixes #48225 TEST= refactoring covered by existing tests, few new tests. Change-Id: Id9fc5af5fe011deb0af3e1e8a4ea3a91799f9da4 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/244241 Reviewed-by: Martin Kustermann <kustermann@google.com> Commit-Queue: Lasse Nielsen <lrn@google.com> |
||
---|---|---|
.. | ||
cast_error | ||
debugger | ||
assertion_failure_message_test.dart | ||
basic_assignment_test.dart | ||
const_test.dart | ||
developer_events_test.dart | ||
hot_restart_expando_test.dart | ||
hot_restart_js_interop_test.dart | ||
hot_restart_late_test.dart | ||
hot_restart_static_test.dart | ||
hot_restart_test.dart | ||
hot_restart_timer_test.dart | ||
if_else_literal_compilation_test.dart | ||
js_interop_test.dart | ||
libraries_part.dart | ||
libraries_test.dart | ||
no_such_method_errors_test.dart | ||
runtime_utils.dart | ||
runtime_utils_nnbd.dart | ||
subtype_test.dart | ||
subtype_weak_test.dart | ||
type_normalization_test.dart | ||
utils.dart | ||
variance_subtype_test.dart | ||
variance_test.dart | ||
weak_null_safety_errors_test.dart |