The ptoblem is when the thread marked as interrupted, it does not release lock on wait(), but throw an InterruptedException immediately.
Dmitrii Krendelev ________________________________________ От: SNMP4J [[email protected]] от имени Dmitrii Krendelev [[email protected]] Отправлено: 18 декабря 2014 г. 23:22 Кому: Frank Fock; [email protected] Тема: [SNMP4J] HA: [BugReport][SNMP4J-2.2.3] Concurrency bug in org.snmp4j.util.ThreadPool. 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 > > > > ________________________________ > The information transmitted herein is intended only for the person or entity > to which it is addressed and may contain confidential, proprietary and/or > privileged material. Any review, retransmission, dissemination or other use > of, or taking of any action in reliance upon, this information by persons or > entities other than the intended recipient is prohibited. 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