Hi,
Here is Version 4:
http://cr.openjdk.java.net/~sjiang/JDK-8007710/04/
1) remove the line
108 vm.resume()
2) call addClassWatch(vm) only when receiving VMStartEvent
3) make sure that the test receives ModificationWatchpointEvent
4) clean
Thanks,
Shanliang
shanliang wrote:
Staffan,
Very nice analysis!
The fix must be very simple, just remove the line
108 vm.resume
it is an error because here the test does not yet treat the events in
eventSet.
the line
136 eventSet.resume();
is the right place to resume the threads after event treatment.
Here is the new webrev:
http://cr.openjdk.java.net/~sjiang/JDK-8007710/03/
Thanks,
Shanliang
Staffan Larsen wrote:
I think I understand what happens now.
The test code, simplified, looks like this (with the Thread.sleep()
added that causes the test to fail):
launchTarget();
addClassWatch();
vm.resume();
Thread.sleep(1000);
while(connected) {
eventSet = eventQueue.remove()
for(event : eventQueue) {
if (event instanceof ClassPrepareEvent) {
addFieldWatch();
}
}
eventSet.resume();
}
By default all events that happen will cause the debuggee to suspend
(see EventRequest.setSuspendPolicy()). Thus when we get to
addFieldWatch(), the vm should be suspended and we should be able to
create the field watch without problem. But the VM isn’t suspended
and that is why the test fail.
Why isn’t the VM suspended? When we get to the “for(event :
eventQueue)” the first time there are *two* events already in the
queue: the VMStartEvent and a ClassPrepareEvent. At this point the VM
is suspended and everything is good. We look at the first eventSet
which only contains the VMStartEvent, we ignore the event, but we
resume the VM. We then loop and look at the ClassPrepareEvent, but by
now the VM is already running and has also terminated. Failure.
Thus, we need to handle the VMStartEvent. I suggest a modification to
my previous code:
launchTarget();
while(connected) {
eventSet = eventQueue.remove()
for(event : eventQueue) {
if (event instanceof VMStartEvent) {
addClassWatch();
}
if (event instanceof ClassPrepareEvent) {
addFieldWatch();
}
}
eventSet.resume();
}
This will cause us to have complete control over the state of the
debuggee. The first event we see will be the VMStartEvent. The VM
will be suspended. We can add a class watch here. Then we resume the
VM. The second event we see will be the ClassPrepareEvent with the VM
suspended. We can add the field watch. Then we resume the VM and wait
for the field watch events.
Thanks,
/Staffan
On 13 feb 2014, at 11:36, shanliang <shanliang.ji...@oracle.com
<mailto:shanliang.ji...@oracle.com>> wrote:
Staffan Larsen wrote:
On 13 feb 2014, at 10:17, Jaroslav Bachorik <jaroslav.bacho...@oracle.com>
wrote:
Hi Staffan,
On 12.2.2014 18:27, Staffan Larsen wrote:
I’m still not happy with this fix since I think the extra output stream
synchronization logic is not needed - the debuggee should be suspended at all
the interesting points. The fix I proposed is cleaner and (as far as I can
tell) also fixes the problem. The only thing is that I can’t quite explain what
goes wrong without the fix… I’d really like to understand that. I’ll try to dig
deeper and see if I can understand exactly what happens.
Yes, bringing the VM to a stable state before calling other JDI functions helps
to stabilize the test even without the additional synchronization via
stdout/stdin.
I just wonder whether this check should not be done inside
com.sun.jdi.connect.LaunchingConnector#launch() implementation. Does it even
make sense to hand off an unstable VM?
Good question, but hard to change now - all implementations depend on the
current functionality. The VMStartEvent also gives you a reference to the main
thread.
The test failed when it received ClassPrepareEvent and did
addFieldWatch, that meant the test must receive already
VMStartEvent, because VMStartEvent must be the first event, if it
was true then the vm must be already stable when failing.
Except that the test received ClassPrepareEvent before VMStartEvent
then it was doing addFieldWatch with a possibly unstable VM. in this
case we might have a serious bug in VirtualMachine implementation,
and if this is true the fix proposed to check "start" may make miss
ClassPrepareEvent, then the test would test nothing.
Shanliang
/S
-JB-
/Staffan
On 12 feb 2014, at 18:04, shanliang <shanliang.ji...@oracle.com> wrote:
Staffan Larsen wrote:
I think what you need to do is wait for the VMStartEvent before you add
requests to the VM. Note this paragraph from the VirtualMachine doc:
Note that a target VM launched by a launching connector is not
guaranteed to be stable until after the VMStartEvent has been
received.
I may miss something here, I believe VMStartEvent must be the first event, when
the test got ClassPrepareEvent, it must already received VMStartEvent.
I think adding code that looks something like this will make the test stable:
VirtualMachine vm = launchTarget(CLASS_NAME);
EventQueue eventQueue = vm.eventQueue();
boolean started = false;
while(!started) {
EventSet eventSet = eventQueue.remove();
for (Event event : eventSet) {
if (event instanceof VMStartEvent) {
started = true;
}
if (event instanceof VMDeathEvent
|| event instanceof VMDisconnectEvent) {
throw new Error("VM died before it started...:"+event);
}
}
}
System.out.println("Vm launched");
The code you proposed could improve the test, it made sure that
TestPostFieldModification was started, but I am afraid that it did not address
the issue causing the failure, the issue I believe was that
TestPostFieldModification exited before or during FieldMonitor called
addFieldWatch(), that was why addFieldWatch() received VMDisconnectedException.
When the test was treating ClassPrepareEvent, even if VMDeathEvent or
VMDisconnectEvent arrived, it must be still waiting in the eventQueue because
it arrived after ClassPrepareEvent.
My fix was to not allow TestPostFieldModification to exit before
addFieldWatch() was done.
There is also no reason to call addFieldWatch() before the ClassPrepareEvent
has been received. The call to vm..classesByName() will just return an empty
list anyway.
I do not know why the test called addFieldWatch before ClassPrepareEvent had
been received, but yes the returned list was empty, so agree to remove it.
While you are in there you can also remove the unused StringBuffer near the top
of main().
Yes it was already removed in version 01
Here is the new webrev:
http://cr.openjdk.java.net/~sjiang/JDK-8007710/02/
Thanks,
Shanliang
Thanks,
/Staffan
On 11 feb 2014, at 18:30, shanliang <shanliang.ji...@oracle.com> wrote:
Here is the new fix in which FieldMonitor will write to
TestPostFieldModification, to inform the latter to quit, as suggested bu
Jaroslav
http://cr.openjdk.java.net/~sjiang/JDK-8007710/01/
Thanks,
Shanliang
shanliang wrote:
shanliang wrote:
Jaroslav Bachorik wrote:
On 11.2.2014 16:31, shanliang wrote:
Staffan Larsen wrote:
Hi Shanliang,
I can’t quite see how the test can fail in this way. When the
ClassPrepareEvent happens, the debuggee will be suspended. So when
addFieldWatch() is called, the debuggee should not have moved.
I am not expert of jdi so I may miss something here. I checked the
failure trace and saw the report exception happen when FieldMonitor
received ClassPrepareEvent and was doing addFieldWatch. FieldMonitor did
call "vm.resume()" before treating events.
AFAICS, calling vm.resume() results in an almost immediate debuggee death. The gc()
invoking thread "d" is flagged as a deamon and as such doesn't prevent the
process from exiting. The other thread is not a daemon but will finish in only few cycles.
I looked at the class com.sun.jdi.VirtualMachine, here is the Javadoc of the method
"resume":
/**
* Continues the execution of the application running in this
* virtual machine. All threads are resumed as documented in
* {@link ThreadReference#resume}.
*
* @throws VMCannotBeModifiedException if the VirtualMachine is read-only -
see {@link VirtualMachine#canBeModified()}.
*
* @see #suspend
*/
void resume();
My understanding is that the debuggee resumes to work after this call, instead
to die?
In fact the problem is here, the vm (TestPostFieldModification) should not die
before FieldMonitor finishes addFieldWatch.
Shanliang
I reproduced the bug by add sleep(1000) after vm.resume() but before
calling eventQueue.remove();
It looks like some kind of synchronization between the debugger and the
debuggee is necessary. But I wonder if you should better use the
process.getOuptuptStream() to write and flush a message for the debugee
indicating that it can exit. And in the debugee you would just do
System.in.read() as the last statement in the main() method. Seems more robust
than involving files.
It could work, but creating a file in the testing directory should have no
issue, but yes maybe less performance.
Thanks,
Shanliang
Cheers,
-JB-
Thanks,
Shanliang
One problem I do see with the test is that it does not wait for a
VMStartEvent before setting up requests. I’m not sure if that could
cause the failure in the bug report, though.
/Staffan
On 11 feb 2014, at 15:13, shanliang <shanliang.ji...@oracle.com> wrote:
Hi ,
The problem could be that FieldMonitor did not have enough time to
"addFieldWatch" but the vm to monitor (TestPostFieldModification) was
already ended.
So we should make sure that TestPostFieldModification exits after
FieldMonitor has done necessary. The solution proposed here is that
FieldMonitor creates a file after adding field watching, and
TestPostFieldModification quits only after finding the file.
web:
http://icncweb.fr.oracle.com/~shjiang/webrev/8007710/00/
bug:
https://bugs.openjdk.java.net/browse/JDK-8007710
Thanks,
Shanliang
