Scala检查外部进程ID（pid）当前是否正在运行？

Question

I need to check if a specified process is currently running using Scala.

All I have is the PID.

Does Scala have an internal function or do I need to parse it using ps ?

Thank you.

Answer 1

You can import sys.process._

General example

import sys.process._
scala> import sys.process._
import sys.process._

scala> "ps" !

PID TTY           TIME CMD
570 ttys000    0:00.02 -bash
591 ttys000    0:00.01 bash /usr/local/bin/scala

getting the PID for the process scala

// !! to get result as String
scala> "\\d+".r.findFirstIn( "ps" #| "grep /usr/local/bin/scala" !! )
res9: Option[String] = Some(591)

for a more information see: http://www.scala-lang.org/api/current/index.html#scala.sys.process.package

Answer 2

When running Scala on Java 9 , we can take advantage of Java 's ProcessHandle which makes it easier to identify and work with native processes:

ProcessHandle.of(5210) match { case p => p.isPresent && p.get.isAlive }

where 5210 is the pid of the process you're interested in getting the status for.

This:

• First creates a Java Optional<ProcessHandle> from the given pid .

• If the process exists, this Optional must be present (which might be enough to tell if the process is alive depending on the system).

• And finally checks that the process is alive using ProcessHandle::isAlive .

No import necessary as ProcessHandle is part of java.lang .

Answer 3

AFAIK, Java or Scala doesn't have such functionality. If you are on UNIX based machine, yes, your best bet is to use ps command.

You can use the PID with ps command as follows:

ps -p 8238 -o "pid="

Here PID is 8283, and we ask ps to search for it, and if it exists, just print it.

scala> import sys.process._
import sys.process._

scala> def processExists(pid: Int) = pid == {try { (List("ps", "-p", s"$pid", "-o", "pid=") !!).trim.toInt } catch { case _: Throwable => -1 }}
warning: there was one feature warning; re-run with -feature for details
processExists: (pid: Int)Boolean

scala> val pid = 8238
pid: Int = 8238

scala> processExists(pid)
res11: Boolean = true

scala> processExists(1234)
res12: Boolean = false