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Experimental platform isolates API #48551
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@@ -10,4 +10,5 @@ | |
| Spawn; | ||
| LoadLibraryFromKernel; | ||
| LookupEntryPoint; | ||
| ForceShutdownIsolate; | ||
| }; | ||
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@@ -9,3 +9,4 @@ _kInternalFlutterGpu* | |
| _Spawn | ||
| _LoadLibraryFromKernel | ||
| _LookupEntryPoint | ||
| _ForceShutdownIsolate | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,189 @@ | ||
| // Copyright 2013 The Flutter Authors. 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.ui; | ||
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| /// Runs [computation] on the platform thread and returns the result. | ||
| /// | ||
|
Member
There was a problem hiding this comment. If the platform doesn't support a platform thread (or it wasn't implemented) - e.g. like jason mentions linux desktop embedder - this function will throw. |
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| /// This may run the computation on a separate isolate. That isolate will be | ||
| /// reused for subsequent [runOnPlatformThread] calls. This means that global | ||
| /// state is maintained in that isolate between calls. | ||
| /// | ||
| /// The [computation] and any state it captures may be sent to that isolate. | ||
| /// See [SendPort.send] for information about what types can be sent. | ||
| /// | ||
| /// If [computation] is asynchronous (returns a `Future<R>`) then | ||
| /// that future is awaited in the new isolate, completing the entire | ||
| /// asynchronous computation, before returning the result. | ||
| /// | ||
| /// If [computation] throws, the `Future` returned by this function completes | ||
| /// with that error. | ||
| /// | ||
| /// The [computation] function and its result (or error) must be | ||
| /// sendable between isolates. Objects that cannot be sent include open | ||
| /// files and sockets (see [SendPort.send] for details). | ||
| /// | ||
| /// This method can only be invoked from the main isolate. | ||
|
Member
There was a problem hiding this comment. Maybe we should mark this temporarily as |
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| /// | ||
| /// This API is currently experimental. | ||
| Future<R> runOnPlatformThread<R>(FutureOr<R> Function() computation) { | ||
| if (isRunningOnPlatformThread) { | ||
| return Future<R>(computation); | ||
| } | ||
| final SendPort? sendPort = _platformRunnerSendPort; | ||
| if (sendPort != null) { | ||
| return _sendComputation(sendPort, computation); | ||
| } else { | ||
| return (_platformRunnerSendPortFuture ??= _spawnPlatformIsolate()) | ||
| .then((SendPort port) => _sendComputation(port, computation)); | ||
| } | ||
| } | ||
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| SendPort? _platformRunnerSendPort; | ||
| Future<SendPort>? _platformRunnerSendPortFuture; | ||
| final Map<int, Completer<Object?>> _pending = <int, Completer<Object?>>{}; | ||
| int _nextId = 0; | ||
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| Future<SendPort> _spawnPlatformIsolate() { | ||
| final Completer<SendPort> sendPortCompleter = Completer<SendPort>(); | ||
| final RawReceivePort receiver = RawReceivePort()..keepIsolateAlive = false; | ||
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Member
There was a problem hiding this comment. When we later allow calling this from a helper isolates, we may want to // When scheduling a computation
if (_pending.isEmpty) {
receiver.keepIsolateAlive = true;
}
_pending[nextId++] = ...
// When getting result
... = _pending.removeAt(id);
if (_pending.isEmpty) receiver.keepIsolateAlive = false;Consider leaving a comment (the |
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| receiver.handler = (Object? message) { | ||
| if (message == null) { | ||
| // This is the platform isolate's onExit handler. | ||
|
Member
There was a problem hiding this comment. Are we actually registering an exit handler (don't see where)? Either we should throw an error if we think this cannot happen or we should just complete all pending RPCs with an error - but not silently ignore it.
Contributor
Author
There was a problem hiding this comment. Jason's comment mentions how to make a private test-only API, so I can now implement and test this logic. |
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| // This shouldn't really happen, since Isolate.exit is disabled, the | ||
| // pause and terminate capabilities aren't provided to the parent | ||
| // isolate, and errors are fatal is false. But if the isolate does | ||
| // shutdown unexpectedly, clear the singleton so we can create another. | ||
| for (final Completer<Object?> completer in _pending.values) { | ||
| completer.completeError(RemoteError( | ||
| 'PlatformIsolate shutdown unexpectedly', | ||
| StackTrace.empty.toString())); | ||
| } | ||
| _pending.clear(); | ||
| _platformRunnerSendPort = null; | ||
| _platformRunnerSendPortFuture = null; | ||
| } else if (message is _PlatformIsolateReadyMessage) { | ||
| _platformRunnerSendPort = message.computationPort; | ||
| sendPortCompleter.complete(message.computationPort); | ||
| } else if (message is _ComputationResult) { | ||
| final Completer<Object?> resultCompleter = _pending.remove(message.id)!; | ||
| final Object? remoteStack = message.remoteStack; | ||
| final Object? remoteError = message.remoteError; | ||
| if (remoteStack != null) { | ||
| if (remoteStack is StackTrace) { | ||
| // Typed error. | ||
| resultCompleter.completeError(remoteError!, remoteStack); | ||
| } else { | ||
| // onError handler message, uncaught async error. | ||
| // Both values are strings, so calling `toString` is efficient. | ||
| final RemoteError error = | ||
| RemoteError(remoteError!.toString(), remoteStack.toString()); | ||
| resultCompleter.completeError(error, error.stackTrace); | ||
| } | ||
| } else { | ||
| resultCompleter.complete(message.result); | ||
| } | ||
| } else { | ||
| // We encountered an error while starting the new isolate. | ||
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Member
There was a problem hiding this comment. If that's true, shouldn't it be sendPortCompleter.completeError(...);maybe make it if (!sendPortCompleter.isCompleted) {
sendPortCompleter.completeError(...);
return;
}
throw ...("unexpected message: $message"); |
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| if (!sendPortCompleter.isCompleted) { | ||
| sendPortCompleter.completeError( | ||
| IsolateSpawnException('Unable to spawn isolate: $message')); | ||
| return; | ||
| } | ||
| // This shouldn't happen. | ||
| throw IsolateSpawnException( | ||
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Member
There was a problem hiding this comment. Not really related to spawning, is it? Maybe
Contributor
Author
There was a problem hiding this comment. Removed, per your other comment |
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| "Internal error: unexpected message: '$message'"); | ||
| } | ||
| }; | ||
| final Isolate parentIsolate = Isolate.current; | ||
| final SendPort sendPort = receiver.sendPort; | ||
| try { | ||
| _nativeSpawn(() => _platformIsolateMain(parentIsolate, sendPort)); | ||
| } on Object { | ||
| receiver.close(); | ||
| rethrow; | ||
| } | ||
| return sendPortCompleter.future; | ||
| } | ||
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| Future<R> _sendComputation<R>( | ||
| SendPort port, FutureOr<R> Function() computation) { | ||
| final int id = ++_nextId; | ||
| final Completer<R> resultCompleter = Completer<R>(); | ||
| _pending[id] = resultCompleter; | ||
| port.send(_ComputationRequest(id, computation)); | ||
| return resultCompleter.future; | ||
| } | ||
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| void _safeSend(SendPort sendPort, int id, Object? result, Object? error, | ||
| Object? stackTrace) { | ||
| try { | ||
| sendPort.send(_ComputationResult(id, result, error, stackTrace)); | ||
| } catch (sendError, sendStack) { | ||
| sendPort.send(_ComputationResult(id, null, sendError, sendStack)); | ||
| } | ||
| } | ||
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| void _platformIsolateMain(Isolate parentIsolate, SendPort sendPort) { | ||
| final RawReceivePort computationPort = RawReceivePort(); | ||
|
Member
There was a problem hiding this comment. It would be nice to avoid repeated port creations (it's expensive, has to go to runtime, ...) - see comment above. |
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| computationPort.handler = (_ComputationRequest? message) { | ||
| if (message == null) { | ||
| // The parent isolate has shutdown. Allow this isolate to shutdown. | ||
| computationPort.keepIsolateAlive = false; | ||
| return; | ||
| } | ||
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| late final FutureOr<Object?> potentiallyAsyncResult; | ||
| try { | ||
| potentiallyAsyncResult = message.computation(); | ||
| } catch (e, s) { | ||
| _safeSend(sendPort, message.id, null, e, s); | ||
| return; | ||
| } | ||
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| if (potentiallyAsyncResult is Future<Object?>) { | ||
| potentiallyAsyncResult.then((Object? result) { | ||
| _safeSend(sendPort, message.id, result, null, null); | ||
| }, onError: (Object? e, Object? s) { | ||
| _safeSend(sendPort, message.id, null, e, s ?? StackTrace.empty); | ||
| }); | ||
| } else { | ||
| _safeSend(sendPort, message.id, potentiallyAsyncResult, null, null); | ||
| } | ||
| }; | ||
| Isolate.current.addOnExitListener(sendPort); | ||
| parentIsolate.addOnExitListener(computationPort.sendPort); | ||
| sendPort.send(_PlatformIsolateReadyMessage(computationPort.sendPort)); | ||
| } | ||
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| @Native<Void Function(Handle)>(symbol: 'PlatformIsolateNativeApi::Spawn') | ||
| external void _nativeSpawn(Function entryPoint); | ||
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| /// Whether the current isolate is running on the platform thread. | ||
| final bool isRunningOnPlatformThread = _isRunningOnPlatformThread(); | ||
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| @Native<Bool Function()>( | ||
| symbol: 'PlatformIsolateNativeApi::IsRunningOnPlatformThread', isLeaf: true) | ||
| external bool _isRunningOnPlatformThread(); | ||
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| class _PlatformIsolateReadyMessage { | ||
| _PlatformIsolateReadyMessage(this.computationPort); | ||
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| final SendPort computationPort; | ||
| } | ||
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| class _ComputationRequest { | ||
| _ComputationRequest(this.id, this.computation); | ||
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| final int id; | ||
| final FutureOr<Object?> Function() computation; | ||
| } | ||
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| class _ComputationResult { | ||
| _ComputationResult(this.id, this.result, this.remoteError, this.remoteStack); | ||
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| final int id; | ||
| final Object? result; | ||
| final Object? remoteError; | ||
| final Object? remoteStack; | ||
| } | ||
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2024
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Flutter uses 2013 throughout its codebase
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That's not what go/copyright (external version https://opensource.google/documentation/reference/copyright) instructs us to do though. It should be the year when the file got first published.
Other coding styles (like Chromium1) seem to adhere to the go/copyright.
Footnotes
https://chromium.googlesource.com/chromium/src/+/HEAD/styleguide/c++/c++.md#file-headers ↩