8:34 a.m.
I have this rule:
rule "Defrost: Turned On"
when
$reading : SwitchReading( switchOn == true ) from entry-point
"ReadingsStream"
not SwitchReading (this.circuit == $reading.circuit, this after $reading
) from entry-point "ReadingsStream"
not DefrostSwitchOn(this.circuit == $reading.circuit)
then
LOG.info("Defrost switch turned on by reading '" + $reading +
"'.");
insert(new DefrostSwitchOn($reading));
end
SwitchReading is an event; DefrostSwitchOn is a POJO fact.
Multiple times I've gotten exceptions where this rule's RHS is called with a
null. The ConsequenceExceptionHandler is supposed to list the facts the RHS
was called with, but it's getting an empty list.
Now, I know my system as it currently stands can take a LONG time between
receiving an event and executing the consequence, primarily when it first
starts and is loading its previous known state. It's entirely believable to
me that the event will have expired before the rule's RHS is called. But
shouldn't the event still be referenced by the Activation?
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9:59 a.m.
The activation contains fact handles, and one must use
workingMemory.getObjct( handle )
to obtain the object - at least a consequence exception handler would do
this.
It is debatable whether long delays are in order when an application is
using real-time event processing. Time-stamped inserts should not be done
before the backlog of restoring everything has been completed.
-W
On 3 November 2011 14:34, Robert Crawford <crawford(a)kloognome.com> wrote:
I have this rule:
rule "Defrost: Turned On"
when
$reading : SwitchReading( switchOn == true ) from entry-point
"ReadingsStream"
not SwitchReading (this.circuit == $reading.circuit, this after $reading
) from entry-point "ReadingsStream"
not DefrostSwitchOn(this.circuit == $reading.circuit)
then
LOG.info("Defrost switch turned on by reading '" + $reading +
"'.");
insert(new DefrostSwitchOn($reading));
end
SwitchReading is an event; DefrostSwitchOn is a POJO fact.
Multiple times I've gotten exceptions where this rule's RHS is called with
a
null. The ConsequenceExceptionHandler is supposed to list the facts the RHS
was called with, but it's getting an empty list.
Now, I know my system as it currently stands can take a LONG time between
receiving an event and executing the consequence, primarily when it first
starts and is loading its previous known state. It's entirely believable to
me that the event will have expired before the rule's RHS is called. But
shouldn't the event still be referenced by the Activation?
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11:15 a.m.
The code being executed is in the DRL file -- and this code USUALLY works.
USUALLY I get the expected object and everything's OK.
I'm trying to move all the long-running code into separate threads, and deal
with occasionally having the same condition detected twice.
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4:03 p.m.
I enhanced my ConsequenceExceptionHandler and have a little more detail on
this. I have this rule:
rule "Duplicate Alerts"
when
$firstAlert : TemperatureAlert( this.saved, this.valid )
$secondAlert : TemperatureAlert (this.location == $firstAlert.location,
this != $firstAlert, this.saved, this.valid )
then
LOG.info("Removing duplicate alert for " + $firstAlert.getLocation());
$secondAlert.setValid(false);
$secondAlert.setInvalidAt(new Date());
update($secondAlert);
end
The TemperatureAlert class is not defined as an event.
I'm getting this exception:
15:56:34,145 ERROR [STDERR] CONSEQUENCE EXCEPTION
15:56:34,145 ERROR [STDERR] Exception executing consequence for rule
"Duplicate Alerts" in xxx.xxxxxxx.rules: java.lang.NullPointerException
15:56:34,145 ERROR [STDERR] START FACT DUMP:
15:56:34,145 ERROR [STDERR]
$firstAlert:xxx.xxxxxxx.TemperatureAlert@1e3c1689
15:56:34,145 ERROR [STDERR] $secondAlert:null
15:56:34,145 ERROR [STDERR] END FACT DUMP
15:56:34,145 ERROR [STDERR] Exception executing consequence for rule
"Duplicate Alerts" in xxx.xxxxxxx.rules: java.lang.NullPointerException
I don't see how this activation could have ever happened.
If there never was an object that qualified, the activation would never have
been scheduled.
If there was one, but it was updated so it no longer matched or was
retracted, then the activation would have been cancelled.
Everything -- EVERYTHING -- for the session is done within a single thread:
Runnable r = new Runnable() {
public void run() {
while (!shuttingDown) {
try {
session.fireUntilHalt();
while (!commandList.isEmpty()) {
commandList.take().execute();
}
} catch (Throwable t) {
t.printStackTrace();
}
}
}
};
The "commandList" is a BlockingQueue of objects that, when execute() is
called, variously insert, retract, or update objects. All the data feeding
into the session flows through that queue. The halt() method is called
either when the queue gets too long and periodically if it's not empty.
Any ideas?
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12:38 a.m.
The NPE could be triggered by the update call, happens in another rule's
LHS.
It's possible that the fact reference bound to $secondAlert is already gone
by the time that NPE happens - I'm not sure about that.
-W
On 17 November 2011 23:03, Robert Crawford <crawford(a)kloognome.com> wrote:
I enhanced my ConsequenceExceptionHandler and have a little more
detail on
this. I have this rule:
rule "Duplicate Alerts"
when
$firstAlert : TemperatureAlert( this.saved, this.valid )
$secondAlert : TemperatureAlert (this.location == $firstAlert.location,
this != $firstAlert, this.saved, this.valid )
then
LOG.info("Removing duplicate alert for " + $firstAlert.getLocation());
$secondAlert.setValid(false);
$secondAlert.setInvalidAt(new Date());
update($secondAlert);
end
The TemperatureAlert class is not defined as an event.
I'm getting this exception:
15:56:34,145 ERROR [STDERR] CONSEQUENCE EXCEPTION
15:56:34,145 ERROR [STDERR] Exception executing consequence for rule
"Duplicate Alerts" in xxx.xxxxxxx.rules: java.lang.NullPointerException
15:56:34,145 ERROR [STDERR] START FACT DUMP:
15:56:34,145 ERROR [STDERR]
$firstAlert:xxx.xxxxxxx.TemperatureAlert@1e3c1689
15:56:34,145 ERROR [STDERR] $secondAlert:null
15:56:34,145 ERROR [STDERR] END FACT DUMP
15:56:34,145 ERROR [STDERR] Exception executing consequence for rule
"Duplicate Alerts" in xxx.xxxxxxx.rules: java.lang.NullPointerException
I don't see how this activation could have ever happened.
If there never was an object that qualified, the activation would never
have
been scheduled.
If there was one, but it was updated so it no longer matched or was
retracted, then the activation would have been cancelled.
Everything -- EVERYTHING -- for the session is done within a single thread:
Runnable r = new Runnable() {
public void run() {
while (!shuttingDown) {
try {
session.fireUntilHalt();
while (!commandList.isEmpty()) {
commandList.take().execute();
}
} catch (Throwable t) {
t.printStackTrace();
}
}
}
};
The "commandList" is a BlockingQueue of objects that, when execute() is
called, variously insert, retract, or update objects. All the data feeding
into the session flows through that queue. The halt() method is called
either when the queue gets too long and periodically if it's not empty.
Any ideas?
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11:45 a.m.
Another clue: these errors nearly disappear when I change garbage collection
settings. I hesitate to say they completely disappear, but in an hour of
running I've only seen one exception thrown from inside Drools code, as
opposed to many dozens before.
The difference is the presence of the options "-XX:+UseConcMarkSweepGC
-XX:+CMSIncrementalMode". If I run with those, I get activations with null
parameters. Without them, I don't.
I don't think Drools uses WeakReferences for anything, but I haven't been
through all the code. Could something like that be happening? Could the
objects be subjected to GC before the activation is created or fires?
Oh, I've also added an AgendaListenerEvent that examines the activations for
this condition and logs it happening.
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participants (2)
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Robert Crawford -
Wolfgang Laun