TransactionReaper may execute continuously

JBossTS TransactionReaper contains a bug which results in the reaper executing continuously within dynamic mode, rather than pausing between runs.

The ReaperThread calls the TransactionReaper.checkingPeriod() method to determine how long it should pause before it can invoke the TransactionReaper.check() method, however there exists a circumstance where the checkingPeriod() will return a negative period for a sustained time, resulting in the thread executing continuously. This occurs when the check() method is invoked while there are existing transactions in the ReaperElementManager.

The check and checkingPeriod methods use the nextDynamicCheckTime variable to store the absolute time at which the next invocation of check should occur, checkingPeriod returns the difference between that time and the current.

When the check method is executed after nextDynamicCheckTime has occurred, the method retrieves the first ReaperElement from the ReaperElementManager. The processing continues as follows

• if no reaperElement present, reset nextDynamicCheckTime to Long.MAX_VALUE
• if present and expired (reaperElement.getAbsoluteTimeout() <= now) then the element is processed
• if present and not expired (reaperElement.getAbsoluteTimeout() > now) then do nothing.

It is the last behaviour which is incorrect as the nextDynamicCheckTime still refers to the previous absolute timeout, i.e. < now, resulting in all calls to checkinPeriod() returning a negative value.

This will only be halted if one of the other conditions is true, i.e. the ReaperElementManager is empty or the head element must be processed by this thread.