问

两个承诺完成时的消防行动

秋梯田那路77 发布于 2023-02-07 10:47

future

我希望在两项承诺成功的情况下完成一些行动.所以我创建了这样一段代码:

val promiseForPersistence = Promise[Unit]()
val promiseForReplication = Promise[Unit]()

promiseForPersistence.future.onComplete {
  case scala.util.Success(_) => {
    if (promiseForReplication.isCompleted) {
      println(s"Acking from persistence promise (replication one already completed)" )
    }
  }
  case _ =>
}

promiseForReplication.future.onComplete {
  case scala.util.Success(_) => {
    if (promiseForPersistence.isCompleted) {
      println(s"Acking from replication promise (persistence one already completed)" )
    }
  }
  case _ =>
}

promiseForPersistence.success()
promiseForReplication.success()

问题是,两个日志消息都被打印出来.我希望动作只被触发一次.为什么它会被解雇两次,怎么才能让它开火一次？

1 个回答

您不应该为此目的使用isCompleted方法Future.你应该在一个未来使用flatMap这样的结合2个期货:
```
for {
  _ <- promiseForPersistence.future
  _ <- promiseForReplication.future
} println("Both are completed" )
```
onComplete两个Promises完成后,可以评估回调.所以你会得到isCompleted == true回调和2条println消息.

有效的方法是在回调中添加回调:
```
promiseForPersistence.future.onSuccess { _ =>
  promiseForReplication.future.onSuccess { _ =>
    println(s"Acking from replication promise (persistence one already completed)" )
  }
}
```
您将获得与flatMap(for-comprehension)完全相同的行为,但语法更简洁.
2023-02-07 10:49 回答

您是漂亮女人807

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