为什么我的Android运行时进程有时会挂在waitFor（）上？

Question

I'm using a Process to ping a computer on my network. (this is in an android app that I'm working on)

public int pingHost(String host) throws IOException, InterruptedException {
    String cmd = "/system/bin/ping -c 1 -W 1000 " + host;
    proc = Runtime.getRuntime().exec(cmd);
    BufferedReader input = new BufferedReader(new InputStreamReader(proc.getErrorStream()));
    String line;
    while ((line = input.readLine()) != null) {
        System.out.println(line);
    }
    proc.waitFor();

    input.close();
    return proc.exitValue();
}

This method is called and determines whether the ping was successful or not based on the exitValue the process provides. With most hosts on my network that I've tested this pingHost() method with, I do get an exit value and respond with an appropriate message.(ping successful/ping failed). But with one specific host on my network, an exitValue is NEVER returned. Why does this happen?

I've found people that have come across similar issues as this, but the solutions that were provided to them haven't helped me. The process still hangs. No error is provided. Any suggestions?

I've tried adding a thread that is started before waitFor() is called... the thread sleeps for 3 seconds and then destroys the process, but this doesn't help. Is there a different problem that I'm not thinking of?

Apparently a new waitFor() method was added in Java 8 that allowed a timeout parameter... my IDE is set to use jdk1.8.0_65 but this method isn't available to me. Is there something I forgot to do?

Answer 1

To answer the question of "pinging" a machine in network, you can use the:

InetAddress.getByName(host).isReachable(timeout)

Documentation:

Tries to reach this InetAddress . This method first tries to use ICMP (ICMP ECHO REQUEST), falling back to a TCP connection on port 7 (Echo) of the remote host.

This function will try ping the host, and return a positive/negative result. The good thing is that this will handle most Linux/Windows/Whatever is "under the hood" of your Android device. Even if you do not have access to the ping binary, or if its somewhere else in your device, and even if the path to the binary is unset.