Hi, Frank,
Thanks for answer!
> ... if no TaskManager is there to handle the task.
To become available, TaskManager need to execute section below
synchronized (ThreadPool.this)
{
this.task = null;
ThreadPool.this.notify();
}
But ThreadPool.this is blocked by synchronized 'execute' method, so
TaskManager-threads will never be available. And when we reach wait() method
again, InterruptedException will be thrown again, so here is a cycle! We do not
unlock the ThreadPool.this!
(http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html ) This process
will never stop since once we got an InterruptedException.
Dmitrii Krendelev
________________________________________
От: SNMP4J [[email protected]] от имени Frank Fock [[email protected]]
Отправлено: 18 декабря 2014 г. 22:43
Кому: [email protected]
Тема: Re: [SNMP4J] [BugReport][SNMP4J-2.2.3] Concurrency bug in
org.snmp4j.util.ThreadPool.
Hi Dimitrii,
When an InterruptedException is thrown in wait() it will be catched and
a new interrupt()
will be triggered. If not handled, the TaskManager continues in the loop
but then finally
calls wait() again, if no TaskManager is there to handle the task.
I do not see any problem with the original code (which is different from
what you quoted
below).
Best regards,
Frank
Am 18.12.2014 11:49, schrieb Dmitrii Krendelev:
> 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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