Hi,
The problem is not exactly about snmp protocol or how many devices we call in
parallel. The problem is that org.snmp4j.util.ThreadPool.execute(WorkerTask
task) method handle java.lang.InterruptedException in wrong way. Which lead the
process to go in cycle and keep lock on ThreadPool object (because 'execute'
method is synchronized). So, all the TaskManager-threads a blocked on object
ThreadPool and never end.
To reproduce the problem it is important not only call enough devices to make
all TaskManager threads busy, but also interrupt the main thread (which called
'execute' method). In order to demonstrate that snmp4j's handle
java.lang.InterruptedException incorrectly, let me ask you to run the code
below, which is exactly show what going on in 'execute' method when main thread
is interupted. The thread goes in cycle.
/**
* This class is demonstrated illegal way to handle InterruptedException
* exactly like it is going on in org.snmp4j.util.ThreadPool.execute(WorkerTask
task) method
*/
public class WrongInterruptDemo
{
public static void main (String[] args)
{
final WrongInterruptDemo instance = new WrongInterruptDemo();
Thread t = new Thread(new Runnable()
{
public void run()
{
instance.execute();
}
});
t.start();
t.interrupt();
}
private synchronized void execute()
{
while (true)
{
try
{
System.out.println("before wait()");
wait();
}
catch (InterruptedException e)
{
Thread.currentThread().interrupt();
}
}
}
}
___________________________________________________________________________
Thanks,
Dmitrii Krendelev
___________________________________________________________________________
________________________________________
От: SNMP4J [[email protected]] от имени Brijesh Kumar
[[email protected]]
Отправлено: 18 декабря 2014 г. 20:10
Кому: [email protected]
Тема: [SNMP4J] snmp4j for multiple device
Hi,
I am running snmp4j request for 10 device parallel . I am using snmpv3 . If
all devices is having same set of cred set it works fine.
If any of this having different auth protocol (MD5 or SHA) or privacy protocol
it fails .
I am getting below error
Message processing model 3 returned error: Unsupported security level
Is there any way i can accomplish sending multiple snmpv3 request to different
device parallely ?
Regards
Brijesh
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________________________________________________
From: Dmitrii Krendelev
Sent: Thursday, December 18, 2014 1:49 PM
To: '[email protected]'; '[email protected]'
Subject: [BugReport][SNMP4J-2.2.3] Concurrency bug in
org.snmp4j.util.ThreadPool.
Hi,
We have found quite a critical bug in
org.snmp4j.util.ThreadPool.execute(WorkerTask task) method. It has an execute
method below
public synchronized void execute(WorkerTask task)
{
while (true)
{
// here we check if some TaskManager-thread is free to execute the
task.
try
{
wait(); // wait until some TaskManager-thread notify that it
finished a previous task
}
catch (InterruptedException ex)
{
Thread.currentThread().interrupt();
}
}
}
If InterruptedException is thrown, so our thread goes into cycle and keep the
lock on the ThreadPool object, so TaskManager-threads cannot notify that they
became free as soon as they blocked on the ThreadPool. So if the interrupt was
called when NO TaskManager-threads were free to execute the task, so the
process just hangs.
There is a simple way to fix it. We need just to break the cycle if the process
was interrupted and not to execute task like below.
public synchronized void execute(WorkerTask task)
{
try
{
while (true)
{
// here we check if some TaskManager-thread is free to execute
the task
wait();// wait until some TaskManager-thread notify that it
finished a previous task
}
catch (InterruptedException ex)
{
Thread.currentThread().interrupt();
}
}
Thanks,
Dmitrii Krendelev
________________________________
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