21 lines
571 B
Dart
21 lines
571 B
Dart
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import 'package:meta/meta.dart';
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/// Runs an action once for everyone who asks: a caller while it runs awaits
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/// the same run, and one after it is done gets it done; only a run that
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/// failed is run again by the next caller.
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@internal
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class Once {
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Future<void>? _run;
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/// Runs [action] unless it ran or runs already, and completes with that
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/// run.
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Future<void> run(Future<void> Function() action) async {
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final run = _run ??= action();
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try {
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await run;
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} catch (_) {
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if (identical(_run, run)) _run = null;
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rethrow;
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}
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}
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}
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