无法暂停 Dart 隔离

Question

我希望在 Dart 中创建一个 Isolate，我可以以编程方式暂停和恢复。这是我使用的代码。

import 'dart:io';
import 'dart:isolate';

void main() async {
  print("Starting isolate");
  Isolate isolate;
  ReceivePort receivePort = ReceivePort();
  isolate = await Isolate.spawn(run, receivePort.sendPort);
  print("pausing");
  Capability cap = isolate.pause(isolate.pauseCapability);
  sleep(Duration(seconds: 5));
  print("Resuming");
  isolate.resume(cap);
}

void run(SendPort sendPort) {
  sleep(Duration(seconds: 2));
  print("Woke up, 1");
  sleep(Duration(seconds: 2));
  print("Woke up, 2");
  sleep(Duration(seconds: 2));
  print("Woke up, 3");
  sleep(Duration(seconds: 2));
  print("Woke up, 4");
  sleep(Duration(seconds: 2));
  print("Woke up, 5");
}

我得到一个像 O/P

Starting isolate
pausing
Woke up, 1
Woke up, 2
Resuming
Woke up, 3
Woke up, 4
Woke up, 5

但我想达到

Starting isolate
pausing
<--- 5 second delay --->
Resuming
Woke up, 1
Woke up, 2
Woke up, 3
Woke up, 4
Woke up, 5

但即使在调用 pause() 之后，Isolate 仍会继续运行。我找到了这个答案，它说这是因为在他们的情况下是无限循环，但我没有使用任何循环。那么我在这里做错了什么？

Answer 1

您的问题是您错过了pause有关隔离的文档中的详细信息：

当隔离接收到暂停命令时，它停止处理来自事件循环队列的事件。它仍然可以向队列添加新事件以响应例如定时器或接收端口消息。当隔离恢复时，它开始处理已经入队的事件。

所以pause不会停止方法的执行，而是会确保在当前运行的方法执行后，它将停止从事件队列中提供更多工作。

虽然sleep实现更像是“立即停止所有执行 N 次”，这更符合您的期望：

小心使用它，因为当它在睡眠调用中被阻塞时，不能在隔离中处理异步操作。

为了使您的示例工作，您需要sleep用Future您正在等待的实例替换调用，因为这会在事件队列中添加事件。

import 'dart:async';
import 'dart:io';
import 'dart:isolate';

Future<void> main() async {
  print("Starting isolate");
  Isolate isolate;
  ReceivePort receivePort = ReceivePort();
  isolate = await Isolate.spawn(run, receivePort.sendPort);
  print("pausing");
  Capability cap = isolate.pause(isolate.pauseCapability);
  sleep(const Duration(seconds: 5));
  print("Resuming");
  isolate.resume(cap);
}

Future<void> run(SendPort sendPort) async {
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 1");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 2");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 3");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 4");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 5");
}

输出：

import 'dart:async';
import 'dart:io';
import 'dart:isolate';

Future<void> main() async {
  print("Starting isolate");
  Isolate isolate;
  ReceivePort receivePort = ReceivePort();
  isolate = await Isolate.spawn(run, receivePort.sendPort);
  print("pausing");
  Capability cap = isolate.pause(isolate.pauseCapability);
  sleep(const Duration(seconds: 5));
  print("Resuming");
  isolate.resume(cap);
}

Future<void> run(SendPort sendPort) async {
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 1");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 2");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 3");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 4");
  await Future<void>.delayed(const Duration(seconds: 2));
  print("Woke up, 5");
}