不能Promise.complete只运行Future.onComplete的回调,而不是一直通过ExecutionContext,并且,据我所知,安排Future.onComplete的回调以后可能在另一个线程中运行它？
解决方法
您可以为onComplete提供自己的ExecutionContext,它将在同一个线程上运行代码：
val immediateContext: ExecutionContext = new ExecutionContext {
def execute(runnable: Runnable) {
runnable.run()
}
def reportFailure(cause: Throwable) {}
}
您甚至可以将其隐含,并且对于您希望在另一个线程中执行执行的情况,您可以提供scala.concurrent.ExecutionContext.global或其他一些上下文.
这是一个测试,它是如何工作的：
val immediateContext: ExecutionContext = new ExecutionContext {
override def reportFailure(cause: Throwable): Unit = {}
override def execute(runnable: Runnable): Unit = {
println("Executing")
runnable.run()
println("Executed")
}
}
def testContext(): Unit = {
println("Scheduling on an uncompleted future")
val p = Promise[Int]()
println("Scheduling")
p.future.onComplete { _ => println("Completed") }(immediateContext)
println("Scheduled")
p.complete(Success(5))
println()
println("Scheduling on an already completed future")
val p2 = Promise[Int]().complete(Success(5))
println("Scheduling")
p2.future.map { n =>
println("Mapping")
n * 2
}(immediateContext).onComplete{
case Success(n) => println(s"Completed: $n")
case _ =>
}(immediateContext)
println("Scheduled")
println()
println("Using scala.concurrent.ExecutionContext.global for comparison")
val p3 = Promise[Int]().complete(Success(5))
println("Scheduling")
p3.future.onComplete {
_ => println("Completed")
}(concurrent.ExecutionContext.global)
println("Scheduled")
}
运行testContext()将打印
Scheduling on an uncompleted future Scheduling Scheduled Executing Completed Executed Scheduling on an already completed future Scheduling Executing Mapping Executed Executing Completed: 10 Executed Scheduled Using scala.concurrent.ExecutionContext.global for comparison Scheduling Scheduled Completed
