unfork DDC's copy of most SDK libraries

pkg/dev_compiler/tool/input_sdk/lib/async/schedule_microtask.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-part of dart.async;
-
-typedef void _AsyncCallback();
-
-class _AsyncCallbackEntry {
-  final _AsyncCallback callback;
-  _AsyncCallbackEntry next;
-  _AsyncCallbackEntry(this.callback);
-}
-
-/** Head of single linked list of pending callbacks. */
-_AsyncCallbackEntry _nextCallback;
-/** Tail of single linked list of pending callbacks. */
-_AsyncCallbackEntry _lastCallback;
-/**
- * Tail of priority callbacks added by the currently executing callback.
- *
- * Priority callbacks are put at the beginning of the
- * callback queue, so that if one callback schedules more than one
- * priority callback, they are still enqueued in scheduling order.
- */
-_AsyncCallbackEntry _lastPriorityCallback;
-/**
- * Whether we are currently inside the callback loop.
- *
- * If we are inside the loop, we never need to schedule the loop,
- * even if adding a first element.
- */
-bool _isInCallbackLoop = false;
-
-void _microtaskLoop() {
-  while (_nextCallback != null) {
-    _lastPriorityCallback = null;
-    _AsyncCallbackEntry entry = _nextCallback;
-    _nextCallback = entry.next;
-    if (_nextCallback == null) _lastCallback = null;
-    (entry.callback)();
-  }
-}
-
-void _startMicrotaskLoop() {
-  _isInCallbackLoop = true;
-  try {
-    // Moved to separate function because try-finally prevents
-    // good optimization.
-    _microtaskLoop();
-  } finally {
-    _lastPriorityCallback = null;
-    _isInCallbackLoop = false;
-    if (_nextCallback != null) {
-      _AsyncRun._scheduleImmediate(_startMicrotaskLoop);
-    }
-  }
-}
-
-/**
- * Schedules a callback to be called as a microtask.
- *
- * The microtask is called after all other currently scheduled
- * microtasks, but as part of the current system event.
- */
-void _scheduleAsyncCallback(_AsyncCallback callback) {
-  _AsyncCallbackEntry newEntry = new _AsyncCallbackEntry(callback);
-  if (_nextCallback == null) {
-    _nextCallback = _lastCallback = newEntry;
-    if (!_isInCallbackLoop) {
-      _AsyncRun._scheduleImmediate(_startMicrotaskLoop);
-    }
-  } else {
-    _lastCallback.next = newEntry;
-    _lastCallback = newEntry;
-  }
-}
-
-/**
- * Schedules a callback to be called before all other currently scheduled ones.
- *
- * This callback takes priority over existing scheduled callbacks.
- * It is only used internally to give higher priority to error reporting.
- *
- * Is always run in the root zone.
- */
-void _schedulePriorityAsyncCallback(_AsyncCallback callback) {
-  if (_nextCallback == null) {
-    _scheduleAsyncCallback(callback);
-    _lastPriorityCallback = _lastCallback;
-    return;
-  }
-  _AsyncCallbackEntry entry = new _AsyncCallbackEntry(callback);
-  if (_lastPriorityCallback == null) {
-    entry.next = _nextCallback;
-    _nextCallback = _lastPriorityCallback = entry;
-  } else {
-    entry.next = _lastPriorityCallback.next;
-    _lastPriorityCallback.next = entry;
-    _lastPriorityCallback = entry;
-    if (entry.next == null) {
-      _lastCallback = entry;
-    }
-  }
-}
-
-/**
- * Runs a function asynchronously.
- *
- * Callbacks registered through this function are always executed in order and
- * are guaranteed to run before other asynchronous events (like [Timer] events,
- * or DOM events).
- *
- * **Warning:** it is possible to starve the DOM by registering asynchronous
- * callbacks through this method. For example the following program runs
- * the callbacks without ever giving the Timer callback a chance to execute:
- *
- *     main() {
- *       Timer.run(() { print("executed"); });  // Will never be executed.
- *       foo() {
- *         scheduleMicrotask(foo);  // Schedules [foo] in front of other events.
- *       }
- *       foo();
- *     }
- *
- * ## Other resources
- *
- * * [The Event Loop and Dart](https://www.dartlang.org/articles/event-loop/):
- * Learn how Dart handles the event queue and microtask queue, so you can write
- * better asynchronous code with fewer surprises.
- */
-void scheduleMicrotask(void callback()) {
-  _Zone currentZone = Zone.current;
-  if (identical(_ROOT_ZONE, currentZone)) {
-    // No need to bind the callback. We know that the root's scheduleMicrotask
-    // will be invoked in the root zone.
-    _rootScheduleMicrotask(null, null, _ROOT_ZONE, callback);
-    return;
-  }
-  _ZoneFunction implementation = currentZone._scheduleMicrotask;
-  if (identical(_ROOT_ZONE, implementation.zone) &&
-      _ROOT_ZONE.inSameErrorZone(currentZone)) {
-    _rootScheduleMicrotask(null, null, currentZone,
-                           currentZone.registerCallback(callback));
-    return;
-  }
-  Zone.current.scheduleMicrotask(
-      Zone.current.bindCallback(callback, runGuarded: true));
-}
-
-class _AsyncRun {
-  /** Schedule the given callback before any other event in the event-loop. */
-  external static void _scheduleImmediate(void callback());
-}