Test Done.
========
1.
Hit refresh repeatedly in Outlook express Email Client. This exercised the
POP3 Server. The mail client indicated error in a random mannner but
frequently.
2. Wrote automated test to stess and relibly reproduce POP Server problem.
Here is the test.
--------------------------------------
from poplib import POP3
import thread
from java.lang import Thread
def multipop(thread_count=1,seq=3):
if thread_count == 1:
for i in range(seq):
print Thread.currentThread().getName(),i
pop()
else:
for i in range(thread_count):
thread.start_new_thread(mpop,(1,seq))
def pop(server='localhost',userid='harmeet',password='harmeet'):
a = POP3(server)
print a.getwelcome()
a.user(userid)
a.pass_(password)
a.list()
(numMsgs, totalSize) = a.stat()
for i in range(1, numMsgs + 1):
(header, msg, octets) = a.retr(i)
print "Message ", `i`, ':'
for line in msg:
print ' ' + line
print '-----------------------'
a.quit()
--------------------------------------------------------
ran this test as
// hit pop server with 1 thread, each thread making 3 requests
pop()
// hit pop server with 5 threads, each thread making 5 requests
pop(5,5)
// hit pop server with 10 threads, each thread making 10 requests
pop(10,10)
Test Result
========
Got error response back. Modified code to dump stack trace.
Here are the interesting stack traces.
-----------------------------------------
java.lang.ArrayIndexOutOfBoundsException
at org.apache.avalon.util.BinaryHeap.percolateUpMinHeap(BinaryHeap.java:209)
at org.apache.avalon.util.BinaryHeap.insert(BinaryHeap.java:88)
at
org.apache.cornerstone.blocks.scheduler.DefaultTimeScheduler.rescheduleEntry
(DefaultTimeScheduler.java:130)
at
org.apache.cornerstone.blocks.scheduler.DefaultTimeScheduler.resetTrigger(De
faultTimeScheduler.java:101)
at
org.apache.james.pop3server.POP3Handler.handleConnection(POP3Handler.java:15
0)
at
org.apache.cornerstone.blocks.connection.ConnectionRunner.run(Connection.jav
a:128)
at org.apache.avalon.util.thread.WorkerThread.run(WorkerThread.java:76)
not as frequently, but this was another stack trace
java.lang.NullPointerException
at
org.apache.cornerstone.blocks.scheduler.TimeScheduledEntry.compareTo(TimeSch
eduledEntry.java:106)
at org.apache.avalon.util.BinaryHeap.percolateUpMinHeap(BinaryHeap.java:212)
at org.apache.avalon.util.BinaryHeap.insert(BinaryHeap.java:88)
at
org.apache.cornerstone.blocks.scheduler.DefaultTimeScheduler.rescheduleEntry
(DefaultTimeScheduler.java:130)
at
org.apache.cornerstone.blocks.scheduler.DefaultTimeScheduler.addTrigger(Defa
ultTimeScheduler.java:69)
at
org.apache.james.pop3server.POP3Handler.handleConnection(POP3Handler.java:14
5)
at
org.apache.cornerstone.blocks.connection.ConnectionRunner.run(Connection.jav
a:128)
at org.apache.avalon.util.thread.WorkerThread.run(WorkerThread.java:76)
----------------------------
These stack traces don't occur if there is a gap in client requests or in a
single client request. To me this indicates potential problems with
DefaultTimeScheduler. Has anyone seen such traces.
My code is a few days old, but I did get the latest code and compare the
changes. Did not upgrade. There seem to be inconsistency between Avalon and
James codebase.
What Worked
==========
Wrote a new implementation of scheduler service. This implementation seemed
to work. The tests above worked. :-)
I am attaching the service for your review.
There are some issues with it.
1. It is based on JDK 1.3 java.util.Timer class. I think the server side
code should be able to choose the environment, but this argument may not
work for all. The JDK Timer based mechanism is similar(maybe derived) to
TimeDaemon class from Doug Lea's util.concurrent package. So it would be
easy to make this backward compatible.
2. The service assumes that TimerTrigger is of type PeriodicTimeTrigger. I
found that this is the only trigger usedin the current Avalon and James
codebase, except in tests.Needed to add these methods to PeriodicTimer to
covert to JDK/Doug Lea type schedule manager.
public long getStartTime()
{
return m_startTime;
}
public long getPeriod()
{
return m_period;
}
What are your thoughts. Have you seen simialar problems with scheduler. The
JDK/Doug Lea Trigger mechanism is very different from Avalon. Should Avalon
move and potentially reuse their model ?
Harmeet
P.S: Request - I would appreciate if someone adds the modifications to
PeriodicTimer. This solves a relibility problem for me. The changes to
PeriodicTimer would allow me to plugin into the current codebase cleanly.
- thanks.
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