[SNMP4J] [BugReport][SNMP4J-2.2.3] Concurrency bug in org.snmp4j.util.ThreadPool.

[Frank Fock]

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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