Hello everyone,
I am testing now the mmbase 1.6 rc3 for VPRO digitiaal and getting the
ConcurrentModificationException for almost every scan editor I use. The scan
editors create long running queries. After the errror the connections and
driver of informix are throwing wierd errors.
Bug #3469 says that it fixed the issue, but that is not the case.
The source code of MultiPool version 1.20 is not threadsafe at all if you
ask me.
Threads can just freely get a connection and put it back even when the
JDBCProbe
checks the connections with checktime.
Scenario
thread 1 calls getFree and passes the semaphore.acquire()
thread JDBCProbe . calls checktime
at this point the JDBCProbe is iterating over the busypool collection and
thread 1 can add a connection to the busy pool. The semaphore is locked by
the JDBCProbe, but should still be locked by thread 1.
The scenario continues..
thread JDBCprobe is still running checktime.
thread 1 executes the query
thread 1 calls putback and waits for the JDBCProbe at the statement
semaphore.release();
In this simple scenario (can happen always when JDBCProbe runs)
the ConcurrentModificationException can be thrown at 2 points in time.
when getFree adds a connection to the busypool or when putback removes a
connection.
The system becomes instable when a connection is running longer then
2 minutes and this exception is thrown.
I think this is a big issue in 1.6rc3.
I will write a fix this afternoon to get my project back on track.
Nico Klasens
