[kepler-dev] NIL token
Christopher Brooks
cxh at eecs.berkeley.edu
Wed Mar 29 23:53:18 PST 2006
Hi Tristan,
About empty arrays, what's the type of the elements of an empty array?
Hint: it is the sound of one hand clapping. :-)
(Sorry, it is late here in California)
You could try disabling the check in ArrayToken for empty arrays
and see what happens when you create an empty array and try
to perform an operation on it. My guess is that the type
system will not be able to resolve the type of elements.
I think the issue is that the way the type system works depends on
having some element of the array have a type. If there are no
elements, then it is unclear what the type of the elements would be.
I think we need to differentiate between ArrayTokens that have
one or more nil elements, but also have non-nil elements and
ArrayTokens that are themselves nil, that is, they have no non-nil
elements. Another case is where an array has one or more nil
elements and non non-nil elements
In other words:
{1, nil} or {nil, 1} An array of 2 IntTokens, one of which is nil
{nil} Is this an empty array or an array of size 1?
{nil, nil} This would be an array of size 2.
I'm starting to see nil tokens as the universal token.
I just checked in some changes so that some of the Tokens have their own NIL
token. Token.NIL, DoubleToken.NIL, IntToken.NIL, LongToken.NIL and all
of these NILs are of a new type, "NilType". NilType is losslessly
convertible to (from?) DoubleType, IntType, LongType etc.
I think we need these Token specific NILs so that the convert()
method will work.
For example, IntToken.convert() looks like:
public static IntToken convert(Token token) throws IllegalActionException {
If the Token argument is Token.NIL, we can't just do:
if (token == null || token.isNil()) {
return (IntToken)Token.NIL;
}
because Token.NIL is not an IntToken and we will get a cast exception
at runtime.
Instead, we must do:
if (token == null || token.isNil()) {
return Intoken.NIL;
}
Anyway, if we figure out how the basetypes work, then we can
figure out how to better handle empty arrays.
It could be that an ArrayToken with no elements is a nil
ArrayToken {nil}
Anyway, I checked in a modified version of Jing's example as
$PTII/ptolemy/actor/lib/test/auto/NilTokenTypeTest.xml
This test has a Const with value nil connected to a Test.
However, the output port of the Const is set to type int by
using the configure ports dialog
With my most recent changes, this now test passes.
[There seems to be a bug in the dialog where setting the port back from
int to nothing does not work, the error message still says int]
I'll need to do some cleanup tomorrow on my most recent changes.
_Christopher
--------
How about ArrayTokens? I've got a problem where my workflow goes into
deadlock if an ArrayToken with no values (which of course can't exist)
needs to be sent. And as you should know (or if i'm doing something
wrong), a Token can't be cast to an ArrayToken.
Currently I just have a 2nd output port which sends a boolean indicating
if there are no tokens being sent on the 1st port and have my other
actors check this port before trying to get values from the 1st port.
This works, but I find the extra relations needed can make the workflow
look quite messy, and i don't feel that having programming logic like
this in the workflow is good practice.
I've not been able to find a good explanation for why ArrayTokens can't
be constructed with empty arrays, if someone knows the reason for this
can I get an explanation please?
Christopher Brooks wrote:
> Hi Jing,
> Thanks for the stack trace. I am tied up with getting Ptolemy II
> ready shipping, so time is short. Also, I wanted Edward to see the
> stack trace. If I had a small test, I could check it in to the tree.
> Yep, I should start up kepler . . .
>
> The problem is that TypeLattice.compare() returning
> either CPO.HIGHER or CPO.INCOMPARABLE.
>
> protected void _checkType(Token token) throws IllegalActionException
{
> int compare = TypeLattice.compare(token.getType(), _resolvedType)
;
>
> if ((compare == CPO.HIGHER) || (compare == CPO.INCOMPARABLE)) {
> throw new IllegalActionException(this,
> Line 741: "Run-time type checking failed. Token " + token
> + " with type " + token.getType()
> + " is incompatible with port type: "
> + getType().toString());
> }
> }
>
> One hack would be to modify the code so that we check to see
> if the Token is nil before calling TypeLattice.compare().
> This seems a bit brute force and would require changing at least
> 112 calls to TypeLattice.compare() in the Ptolemy tree.
>
> Another idea would be for each Token to have its own NIL token.
> This seems inelegant.
>
> Perhaps the NIL token needs to have a getType() method that returns
> something that the type lattice will properly type check. A NIL
> token is the univesal token, it can be used anywhere.
>
> Modifying ptolemy.data.Token so it redefines getType might work:
>
> /** A token that represents a missing value.
> * Null or missing tokens are common in analytical systems
> * like R and SAS where they are used to handle sparsely populated d
ata
> * sources. In database parlance, missing tokens are sometimes call
ed
> * null tokens. Since null is a Java keyword, we use the term "nil"
.
> * The toString() method on a nil token returns the string "nil".
> */
> public static final Token NIL = new Token() {
> /** Return the type of this token.
> * @return BaseType.UNKNOWN;
> */
> public Type getType() {
> return BaseType.UNKNOWN;
> }
> };
>
> However, I think we need to instead add a new type, which is the
> type that is specific to NIL. This type is in some ways in
> comparable, but operations such as add can be performed on it.
> TypeLattice.compare() would need to be modified so if one
> of the arguments is the newly defind NIL type, then it returns
> ptolemy.graph.CPO.SAME.
> This seems like a scary change that could affect performance.
>
> If you can send me a small test case that I can add to the Ptolemy
> tree, I can see about hacking something in.
>
> Comments?
>
> _Christopher
>
> --------
>
> Hi, Christopher:
>
> The test workflow is alreay in
> kepler/workflows/test/test-eml-missing-value-field.xml. You may run i
t and
> to see what will happen. The stack trace is:
>
> ptolemy.kernel.util.IllegalActionException: Run-time type checking fa
iled.
> Token nil with type general is incompatible with port type: double
> in .test-eml-missing-value-field.Missing Value.Column2
> at ptolemy.actor.TypedIOPort._checkType(TypedIOPort.java:741)
> at ptolemy.actor.TypedIOPort.send(TypedIOPort.java:463)
> at
> org.ecoinformatics.seek.datasource.eml.eml2.Eml200OutputTypeField.fir
e(Eml2
> 00OutputTypeField.java:103)
> at
> org.ecoinformatics.seek.datasource.eml.eml2.Eml200DataSource.fire(Eml
200Dat
> aSource.java:552)
> at ptolemy.actor.AtomicActor.iterate(AtomicActor.java:309)
> at
> ptolemy.actor.sched.StaticSchedulingDirector.fire(StaticSchedulingDir
ector.
> java:170)
> at ptolemy.actor.CompositeActor.fire(CompositeActor.java:331)
> at ptolemy.actor.Manager.iterate(Manager.java:613)
> at ptolemy.actor.Manager.execute(Manager.java:322)
> at ptolemy.actor.Manager.run(Manager.java:985)
> at ptolemy.actor.Manager$3.run(Manager.java:1026)
>
>
> Thanks,
>
> Jing
>
> Jing Tao
> National Center for Ecological
> Analysis and Synthesis (NCEAS)
> 735 State St. Suite 204
> Santa Barbara, CA 93101
>
> On Wed, 29 Mar 2006, Christopher Brooks wrote:
>
> > Date: Wed, 29 Mar 2006 11:04:25 -0800
> > From: Christopher Brooks <cxh at eecs.berkeley.edu>
> > To: Jing Tao <tao at nceas.ucsb.edu>
> > Cc: kepler-dev at ecoinformatics.org
> > Subject: Re: [kepler-dev] NIL token
> >
> > Hi Jing,
> >
> > Good question, I was afraid there might be issues surrounding
> > Nil tokens and types. My previous design had nil-ness being a
> > property of the token, so we had a DoubleToken that was of
> > type double and was nil. Now we have just one token which is nil.
> >
> > Can you construct a small model that has a similar failure?
> >
> > Also, what's the stack trace of the current failure?
> > Perhaps where the types are being checked needs to be updated to
> > handle nilness
> >
> > _Christopher
> >
> > --------
> >
> > hi, Christopher:
> >
> > According to the changes you made in ptolemy about nil token, I
made t
> he
> > changes in kepler for missing value too.
> >
> > Since currently we only have one public static variable NIL in T
oken c
> lass
> > (NIL is a generic type and there is no any other nil in sub toke
n
> > classes), I think every missing value element should be replaced
by th
> e
> > NIL token no matter what the data type it is. But when I run the
workf
> low
> > test, I got some error:
> >
> > Workflow workflows/test/test-ecogrid-eml-gce-data.xml FAILED:
> > [java] ptolemy.kernel.util.IllegalActionException: Run-time type
check
> ing
> > failed. Token nil with type general is
> > incompatible with port type: int
> >
> > So it seems the NIL token is not compatible to int port type. Di
d I mi
> ss
> > something? How can I make the NIL token to compatible int port t
ype?
> >
> > Thanks,
> >
> > Jing
> >
> > Jing Tao
> > National Center for Ecological
> > Analysis and Synthesis (NCEAS)
> > 735 State St. Suite 204
> > Santa Barbara, CA 93101
> > _______________________________________________
> > Kepler-dev mailing list
> > Kepler-dev at ecoinformatics.org
> > http://mercury.nceas.ucsb.edu/ecoinformatics/mailman/listinfo/ke
pler-d
> ev
> > --------
> >
> >
> --------
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> Kepler-dev mailing list
> Kepler-dev at ecoinformatics.org
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>
--
Tristan King | Ph: (07) 4781 6911
DART project team | Email: Tristan.King at jcu.edu.au
James Cook University | Web: http://dart.edu.au
Townsville QLD 4814 | http://plone.jcu.edu.au/dart/
Australia |
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