Thread: Re: [Asterisk-java-users] unable to logoff()

SourceForge Headquarters 225 Broadway Suite 1600 San Diego, CA 92101 +1 (858) 422-6466

Dear Henry,

thanks for your message! First of all, hats off - you do very well as a 
newcomer to Java!

First of all , run() is a method used with threads. If you intend to use 
threads, you need to inherit your class from java.lang.Thread like so:

public class AMILogin extends Thread
{
     ...
}

This class would then contain the run() method. To instantiate your 
class and start the thread you would then do this:

AMILogin    myLogin = null;

myLogin = new AMILogin ();
myLogin.getCredentials ("192.168.10.12", "admin", "admin");
myLogin.start;  // -> This calls the run() method and starts the thread!

Since you used the run() method and your exception message showed traces 
of GUI activity while at the same time AMILogin doesn't extend 
java.lang.Thread, I followed two possible scenarios:

a)  Class AMILogin is a stand-alone class having no inheritance from 
java.lang.Thread.
     To make this work, I
     * I added a main() method
     * I changed the name of the run() method to login()
     * instantiated AMILogin, did a login and exited.

     With this approach I had no errors.

b)  Class AMILogin does inherit from java.lang.Thread.
     * I added a main() method
     * Program instantiated AMILogin and started the thread.
     * Program logged off immediately.

     With this approach I got a NullPointerException in the logOff 
method as indicated.

=========================================================================
Approach a: No java.lang.Thread:
=========================================================================

--------------- source code 1 start -----------------------------

package org.rww.asterisk.trials;

import java.io.IOException;
import net.sf.asterisk.manager.AuthenticationFailedException;
import net.sf.asterisk.manager.ManagerConnection;
import net.sf.asterisk.manager.ManagerConnectionFactory;
import net.sf.asterisk.manager.TimeoutException;

public class AMILogin
{
     String                   userName;

     String                   hostName;

     String                   passWord;

     ManagerConnection        managerConnection;

     ManagerConnectionFactory factory;

     public void login() throws IOException, AuthenticationFailedException,
             TimeoutException
     {
         factory = new ManagerConnectionFactory();
         this.managerConnection = factory.getManagerConnection(hostName,
                 userName, passWord);
         managerConnection.login();
     }

     public boolean checkLogin()
     {
         if (managerConnection.isConnected())
             return true;
         else
             return false;
     }

     public void getCredentials(String h, String u, String p)
     {
         userName = u;
         hostName = h;
         passWord = p;
     }

     public void logOff() throws java.io.IOException, TimeoutException
     {
         managerConnection.logoff();
     }

     public static void main (String [] args)
     {
         AMILogin l;

         try
         {
             l = new AMILogin ();
             l.getCredentials("192.168.10.12", "admin", "admin");
             System.out.println("=======>  logging in <=======");
             l.login();
             System.out.println("\n=======> logging out <=======");
             l.logOff();
         }
         catch (IOException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (AuthenticationFailedException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (TimeoutException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (InterruptedException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }

     }
}

--------------- source code 1 end -----------------------------

The corresponding console output is:

--------------- output 1 start ---------------------------

=======>  logging in <=======
01-Apr-2006 12:55:14 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connecting to 192.168.10.12 port 5038
01-Apr-2006 12:55:27 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connected via Asterisk Call Manager/1.0
01-Apr-2006 12:55:27 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Successfully logged in
01-Apr-2006 12:55:27 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Determined Asterisk version: Asterisk 1.0

=======> logging out <=======
01-Apr-2006 12:55:32 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Reached end of stream, terminating reader.
01-Apr-2006 12:55:32 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Closing socket.

--------------- output 1  end ---------------------------

So it worked on my machine.

=========================================================================
Approach b: inherit from java.lang.Thread:
=========================================================================

--------------- source code 2 start -----------------------------

package org.rww.asterisk.trials;

import java.io.IOException;
import net.sf.asterisk.manager.AuthenticationFailedException;
import net.sf.asterisk.manager.ManagerConnection;
import net.sf.asterisk.manager.ManagerConnectionFactory;
import net.sf.asterisk.manager.TimeoutException;

public class AMILogin extends Thread
{
     String                   userName;

     String                   hostName;

     String                   passWord;

     ManagerConnection        managerConnection;

     ManagerConnectionFactory factory;

     public void run()
     {
         factory = new ManagerConnectionFactory();
         try
         {
             this.managerConnection = factory.getManagerConnection(hostName,
                     userName, passWord);
             managerConnection.login();
         }
         catch (IOException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (AuthenticationFailedException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         catch (TimeoutException e)
         {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }

     public boolean checkLogin()
     {
         if (managerConnection.isConnected())
             return true;
         else
             return false;
     }

     public void getCredentials(String h, String u, String p)
     {
         userName = u;
         hostName = h;
         passWord = p;
     }

     public void logOff() throws java.io.IOException, TimeoutException
     {
         managerConnection.logoff();
     }

     public static void main (String [] args)
     {
         AMILogin l;

             try
             {
                 l = new AMILogin ();
                 l.getCredentials("192.168.10.12", "admin", "admin");
                 System.out.println("=======>  logging in <=======");
                 l.start();

                 System.out.println("\n=======> logging out <=======");
                 l.logOff();
             }
             catch (IOException e)
             {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
             catch (TimeoutException e)
             {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }

     }
}

--------------- source code 2  end -----------------------------

Lo and behold, now the corresponding console output goes like this:

--------------- output 1 start ---------------------------

=======>  logging in <=======

=======> logging out <=======
Exception in thread "main" java.lang.NullPointerException
	at org.rww.asterisk.trials.AMILogin.logOff(AMILogin.java:70)
	at org.rww.asterisk.trials.AMILogin.main(AMILogin.java:85)
01-Apr-2006 13:01:44 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connecting to 192.168.10.12 port 5038
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connected via Asterisk Call Manager/1.0
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Successfully logged in
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Determined Asterisk version: Asterisk 1.0

--------------- output 1  end ---------------------------

So, now I got the desired NullPointerException! The reason for this lies 
in the timing: The statements in the main() method:

                 l = new AMILogin ();
                 l.getCredentials("192.168.10.12", "admin", "admin");
                 System.out.println("=======>  logging in <=======");
                 l.start();

                 System.out.println("\n=======> logging out <=======");
                 l.logOff();

make the following sequence happen:

1. Create new AMILogin
2. Get Credentials
3. Print "=======>  logging in <=======";
4. Start Thread and RETURN IMMEDIATELY (!!)

Now, my new AMILogin Thread starts. It
4.1.   Logs into the asterisk server
4.2.   Waits (!!) for the asterisk server's response

At point 4.2., no ManagerConnection object exists yet as the call to
     this.managerConnection = factory.getManagerConnection(hostName, 
userName, passWord);

hasn't returned and won't be for the next few seconds. Therefore the 
AMILogin member
     managerConnection

remains null until the server has answered.

But our main() function doesn't wait. Meanwhile it continues:
5. Print "\n=======> logging out <======="
6. Call logoff ();

And at this point, We get the NullPointerException, because in logOff() 
we call
     managerConnection.logoff();

on a non-existing object, as managerConnection  is still  null (since we 
are still waiting for the asterisk server's response).

Then a few seconds later, the server does respond:
01-Apr-2006 13:01:44 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connecting to 192.168.10.12 port 5038
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Connected via Asterisk Call Manager/1.0
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Successfully logged in
01-Apr-2006 13:01:57 net.sf.asterisk.util.impl.JavaLoggingLog info
INFO: Determined Asterisk version: Asterisk 1.0

But now it's too late.

What we have here is called a race condition - two thread race against 
each other and our application gets into a bad state. This is because 
the start() call is an asynchronous call - it sends the start message to 
the thread object and returns immediately. The opposite would be a 
synchronous call where the caller waits for the callee to finish. 
Programming wise, a call to a method / function is mostly synchronous, 
as the caller waits for the function to return.

Some examples to illustrate this:

Asynchronous call: Your boss asks you to create this report (will take 
four to six weeks to completion) and comes back the next day to get the 
result.
Synchronous call: Your boss asks you to create this report (will take 
four to six weeks to completion) and waits for you to come back to him 
and then asks you for the result.

In this example, the main() function is like that impatient boss - it 
tells your poor AMILogin object to login, but then doesn't wait and 
immediately wants to log out. AMILogin object shouts in protest - 
NullPointerException!  as much as our poor employee would answer that 
impatient boss: "Sorry, NullReportException".

Asynchronous call: You order a pizza by phone from a pizza shop. You 
know the pizza will come some time later and forget about the call and 
watch the news meanwhile.
Synchronous call: You go into a pizza restaurant, sit down at a table, 
order a pizza and WAIT for the pizza to be finished. You certainly won't 
forget the order, as you can't do anything until the pizza's done.

As I say, I don't know which scenario (threaded/non threaded) applies to 
your situation. But I hope this information helps.

But there are two example applications on asterisk-java - head to
     http://svn.reucon.net/repos/asterisk-java-examples/trunk/

the ast-console application contains a longer text in the /doc directory 
explaining the application.

Thanks again for your message!

God bless,

Peter

--
dyslexics of the world - untie !

 > Hi all,
 > i'am new to asterisk-java (to be honest to java too), so please be 
clement.
 > I am able to logon into my Asterisk server but have problem to logoff.
 >
 > #java Main
 > 31 mars 2006 16:11:36 net.sf.asterisk.util.impl.JavaLoggingLog info
 > INFO: Connecting to 192.168.204.223 port 5038
 > 31 mars 2006 16:11:37 net.sf.asterisk.util.impl.JavaLoggingLog info
 > INFO: Connected via Asterisk Call Manager/1.0
 > 31 mars 2006 16:11:37 net.sf.asterisk.util.impl.JavaLoggingLog info
 > INFO: Successfully logged in
 > 31 mars 2006 16:11:37 net.sf.asterisk.util.impl.JavaLoggingLog info
 > INFO: Determined Asterisk version: Asterisk 1.0
 > Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
 >         at AMILogin.logOff(AMILogin.java:36)
 >         at MainPage$1.mouseClicked(MainPage.java:50)
 >         at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
 >         at java.awt.Component.processMouseEvent(Unknown Source)
 >         at javax.swing.JComponent.processMouseEvent(Unknown Source)
 >         at java.awt.Component.processEvent(Unknown Source)
 >         at java.awt.Container.processEvent(Unknown Source)
 >         at java.awt.Component.dispatchEventImpl(Unknown Source)
 >         at java.awt.Container.dispatchEventImpl(Unknown Source)
 >         at java.awt.Component.dispatchEvent(Unknown Source)
 >         at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown 
Source=
 > )
 >         at java.awt.LightweightDispatcher.processMouseEvent(Unknown 
Source)
 >         at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
 >         at java.awt.Container.dispatchEventImpl(Unknown Source)
 >         at java.awt.Window.dispatchEventImpl(Unknown Source)
 >         at java.awt.Component.dispatchEvent(Unknown Source)
 >         at java.awt.EventQueue.dispatchEvent(Unknown Source)
 >         at 
java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown So=
 > urce)
 >
 >         at 
java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Sour=
 > ce)
 >         at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 >         at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 >         at java.awt.EventDispatchThread.run(Unknown Source)
 >
 >
 > here what i have...
 >
 >
 > import java.io.IOException;
 > import net.sf.asterisk.manager.AuthenticationFailedException;
 > import net.sf.asterisk.manager.ManagerConnection;
 > import net.sf.asterisk.manager.ManagerConnectionFactory;
 > import net.sf.asterisk.manager.TimeoutException;
 >
 > public class AMILogin
 > {
 >  String userName;
 >  String hostName;
 >  String passWord;
 >  ManagerConnection managerConnection;
 >  ManagerConnectionFactory factory;
 >
 >  public void run() throws IOException, AuthenticationFailedException,
 > TimeoutException
 >  {
 >   factory =3D new ManagerConnectionFactory();
 >   this.managerConnection =3D factory.getManagerConnection(hostName,
 > userName, passWord);
 >   managerConnection.login();
 >  }
 >  public boolean  checkLogin()
 >  {
 >   if(managerConnection.isConnected())
 >    return true;
 >   else
 >    return false;
 >  }
 >  public void getCredentials(String h, String u, String p)
 >  {
 >   userName =3D u;
 >   hostName =3D h;
 >   passWord =3D p;
 >  }
 >  public void logOff()throws java.io.IOException, TimeoutException
 >  {
 >   managerConnection.logoff();
 >  }
 > }
 >
 > Has anyone an idea what is wrong?
 > thx in advance...
 >
 > henry.

Thread: Re: [Asterisk-java-users] unable to logoff()

asterisk-java-users