java - Using a Timer to break a loop -

i trying build timeout call/response ping. determine commport use in auto-connect sequence. when send call_signal byte[], expect "fu" in reply. how determine device. sscce below (sorry length, is shortened version)

import java.io.ioexception; import java.io.inputstream; import java.io.outputstream; import java.util.enumeration; import java.util.timer; import java.util.timertask; import javax.comm.commportidentifier; import javax.comm.commport; import javax.comm.portinuseexception; import javax.comm.serialport;  public class pingtest {     public static final long ping_timeout = 1000; // in millis     public static final byte[] call_signal = {70, 68, 73, 68};      public boolean ping(commportidentifier cpi)  {         system.out.println("pinging " + cpi.getname());         commport port = null;         inputstream input = null;         outputstream output = null;          //initialization test         try {             port = cpi.open("pingtest", 50);             input = port.getinputstream();             output = port.getoutputstream();         } catch (portinuseexception ex) {             if (cpi.getcurrentowner().startswith("pingtest")) {                 system.out.println("port owned application.");                 return true;             }             return false;         } catch (exception ex) {             try {             port.close();             } catch (nullpointerexception e) {             }             system.out.println("failed initialization test.");             system.err.println(ex);             return false;         }         system.out.println("passed initialization test.");           //call , response test         final stop stop = new stop();         timer timer = new timer();         timer.schedule(new timertask() {              @override             public void run() {                 system.out.println("stop timer triggered.");                 stop.shouldstop = true;             }         }, ping_timeout);         try {             system.out.println("writing...");             output.write(call_signal);             system.out.println("reading...");             boolean waitforf = true;             while (!stop.shouldstop && !stop.didpass) {                 if (waitforf) {                     if ((byte) 'f' == input.read()) {                         waitforf = false;                     }                 } else {                     system.out.println('f');                     if ((byte) 'u' == input.read()) {                         system.out.println('u');                         stop.didpass = true;                     } else {                         system.out.println();                         waitforf = true;                     }                 }             }         } catch (ioexception ex) {             system.out.println("failed i/o test.");             return false;         } {             port.close();         }          if (stop.didpass) {             system.out.println("successful ping.");             return true;         }         system.out.println("failed call , response test.");         return false;     }      public static void main(string[] args) {         pingtest pinger = new pingtest();         enumeration<commportidentifier> ports = commportidentifier.getportidentifiers();         boolean trigger = true;         string name = null;         while (trigger && ports.hasmoreelements) {             commportidentifier cpi = ports.nextelement();             name = cpi.getname();             trigger = !ping(cpi);         }         if (trigger) {             system.out.println("found it. " + name);         } else {             system.out.println("not found");         }     } }  class stop {     boolean shouldstop = false;     boolean didpass = false; } 

my output is:

pinging com1 passed initialization test. writing... reading... stop timer triggered. 

and application freezes. there problem trying stop while loop timer?

your reads blocking. need use timeouts