在执行上下文中获取在后台运行的期货数量的最佳方法是什么? [英] what is the best way to get the number of futures running in background in an execution context?

问题描述

我想从单元测试中检查未来是否已完成或取消，并且仍然没有在后台运行消耗 cpu 资源.一种方法是在我开始我的测试方法之前和之后检查期货的数量.最好的方法是什么?

I would like to check from the unit test if the future is completed or cancelled and still not running in the background consuming cpu resources. One way is to check the number of futures before and after i start my test method. whats the best way to do this?

推荐答案

你可以使用像 Thread.getAllStackTraces 到 获取线程及其状态.scala Future 也将在线程上运行.

You can use something as simple as Thread.getAllStackTraces to get the threads and their states. scala Future will run on thread as well.

import java.lang.management.ManagementFactory

import scala.concurrent.ExecutionContext

object ThreadUsage {

  def main(args: Array[String]): Unit = {
    val ex = ExecutionContext.Implicits.global

    ex.execute(new Thread(() => {
      println("executing timed task")
      Thread.sleep(2000)
    }))

    // equivalent Future {}
    // import scala.concurrent.Future
    // Future {
    //  println("executing timed task")
    //  Thread.sleep(2000)
    // } (ex)

    ex.execute(new Thread(() => {
      println("executing quick task")
    }))

    val running = Thread.getAllStackTraces.keySet()
    running.forEach(a => {
      val bean = ManagementFactory.getThreadMXBean
      println(a.getThreadGroup + "   " + 
              a.getName + "   " + 
              a.getState + "   " +   
              (bean.getCurrentThreadCpuTime / (1000 * 1000)) + "ms"
      )
    })
  }
}

这将给出上面应用程序中产生的两个线程的状态，

which will give the state of two threads spawn in above app,

• scala-execution-context-global-12
• scala-execution-context-global-14

输出:

executing timed task
executing quick task
java.lang.ThreadGroup[name=main,maxpri=10]   scala-execution-context-global-14   WAITING   528ms
java.lang.ThreadGroup[name=system,maxpri=10]   Reference Handler   WAITING   528ms
java.lang.ThreadGroup[name=main,maxpri=10]   Monitor Ctrl-Break   RUNNABLE   528ms
java.lang.ThreadGroup[name=main,maxpri=10]   main   RUNNABLE   528ms
java.lang.ThreadGroup[name=main,maxpri=10]   scala-execution-context-global-12   TIMED_WAITING   528ms
java.lang.ThreadGroup[name=system,maxpri=10]   Signal Dispatcher   RUNNABLE   528ms
java.lang.ThreadGroup[name=system,maxpri=10]   Finalizer   WAITING   528ms

您可以改为使用图形工具，例如 jmc(java 任务控制) 和 jconsole 查看正在运行的线程及其 CPU 使用率等.

You can instead use graphic tool like jmc (java mission control) and jconsole to see the running threads with their CPU usage and all.

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