[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
https://issues.apache.org/jira/browse/MATH-742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13211878#comment-13211878
]
Neil Roeth commented on MATH-742:
-
Of course, I'm fine moving the general discussion elsewhere. IIRC, that
suggestion was made earlier in this thread by someone. :-) To answer your
specific questions:
bq. I don't understand why the idiom would break down with the addition of a
private field; the only requirement is that a class provides accessors to
everything one needs to reconstruct an identical object.
I meant private fields with no public accessors, and the requirement you state
is precisely the one that would make the class impossible to serialize with the
idiom while it would be possible with the other methods.
bq. Could you give a concrete example where one would need to serialize a RNG
(where it must continue drawing from the same sequence)?
Pretty much any RNG should continue using the same sequence rather than
restarting from a new seed if the sequences are meant to model the same random
element. So, a calculation where you do part of the calculation, do some
processing, then do some calculation might be an example. However, evaluating
whether this particular case needs to be serialized is missing the point. The
point is that there are classes (like this RNG) where the constructor
preconditions that the idiom depends upon are nowhere near sufficient to
guarantee that an identical object can be created. If you prefer, think of
class A with a constructor that takes an argument of class B, then creates from
that an internal instance of class C that is required to completely define the
state of an instance of A. There is no public accessor for C because that
field has no meaning outside of the class itself. The instance of class B used
to construct the instance of A is useless after the object is constructed, so
it is not saved and therefore is not available at serialization/deserialization
time to construct a new instance. The idiom cannot handle that, but the default
serialization or explicit writeObject() and readObject() methods can (as long
as class C is made Serializable).
I would be happy to respond to the other, more general points, but since you
asked to suspend further comments on the general issue and others are probably
tired of the discussion :-), I'll not do so.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
https://issues.apache.org/jira/browse/MATH-742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13211388#comment-13211388
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Neil Roeth commented on MATH-742:
-
Responding to Luc:
bq. I think we can simply say this is not supported. Serialization should not
be used for long time storage, and even if it can be used for distributed
computation with different versions between client and server, we can simply
say we don't support it.
Completely reasonable.
bq. +1 for the concerns of a library, but there are many cases when a simple
implements Serializable is sufficient and does not imply too much work.
Yes, agreed. I think this is one of them.
Responding to Gilles:
bq. There is no encapsulation breaking: The code uses only public accessors
in order to extract the objectively meaningful data that are needed to define
the concept represented by PolynomialSplineFunction (the knots and the set of
coefficients of the polynomial functions that are connected at the knots).
Well, yes, but add a private field critical to the state of PolynomialFunction
and the idiom breaks down. There would be no breakdown if the class itself
were responsible for ensuring that readObject() and writeObject() did the right
thing.
Here's an example: Suppose you have a random number generator class RngGilles
that has a constructor that takes a single long integer as an argument. The
constructor precondition returns true for any value of the long integer. With
that long integer, it initializes a private table of several hundred long
integers and a private marker of its current position in the table. When
RngGilles.nextRandom() is called, it calculates the value to be returned from
the table and its current place in the table , then updates the table and its
current place, then returns the value. It does this a billion times, then
needs to be serialized and deserialized in order to continue to use that same
random number sequence in another process. The idiom would fail in that case,
while the default writeObject() and readObject() would succeed.
bq. In some sense, the default serialization breaks the encapsulation because
the object is deserialized without undergoing the constructor's precondition
checks; while the SerializationProxy actually enforces encapsulation by
passing the deserialized to the constructor.
I understand what you are saying, but the concept of serialization is that when
you are done deserializing, you have an object that represents the exact same
state as the object that was serialized, so since it already satisfied any
constructor preconditions when it was first created, there is no need to check
them again. It is, of course, possible to subvert this for some particular
class, e.g., through poorly written explicit writeObject() and readObject()
methods, or by failing to mark some fields transient and making methods that
use the transient field handle that, but I'd call that a bug in that particular
object's serialization implementation, not a general failure of serialization
that needs to be handled outside the class by serialization wrappers. ISTM
that the idiom basically boils down to deconstructing objects to their
primitive fields and then reconstructing them from those primitives, completely
bypassing the whole Serialization mechanism except for those primitive fields.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
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]
Neil Roeth commented on MATH-742:
-
First, thanks for continuing to respond, I do want to understand the reasoning
behind this decision and you are helping make it clear.
{quote}
We are already in trouble, because of this lack of policy, for several classes
for which Serializable is a supposedly innocuous feature (e.g. fields that
should be transient cannot be because no explicit serialization is implemented).
{quote}
Do you mean that if you corrected this and made them transient, you would
introduce an incompatibility with objects serialized using older versions of
the class? If not that, then could you explain?
{quote}
In the Commons project, there is a commitment that minor releases must be fully
compatible; that implies that relying on a default serialization would prevent
any change to internal structure of a class.
{quote}
I understand completely about not making changes in minor releases. Since that
commitment is for minor releases, that implies that it could be done at the
next major release, right?
{quote}
Maybe that you are not aware of the constraints imposed by Serializable;
maybe that you don't care because in your use-case, you'll never be confronted
to the problem of a wrong serialized form. But another user's use-case might
bring him here complaining about our inconsistent support of Serializable.
Would he be less right than you?
{quote}
Not aware is more likely than don't care. I may be ignorant but I'm not
callous. :-) I understand that suddenly changing how a class is serialized
could break things for use cases other than mine and that is no less right than
mine. Another reason to restrict the change to a major version.
{quote}
It is always trivial to add implements Serializable to a class definition.
But it is not trivial to do the implementation in the right way; just adding
implements Serializable is not the right way, never. Again, it could be good
enough for some purpose, but the wish for CM to be an example of good Java
programming, is not compatible with statements such as We know it's sloppy, so
don't use it whenever you need something that works
{quote}
This is the core of the issue. I can see that implementing Serializable might
require special code in some cases, but why is just adding implements
Serializable _never_ the right way? You provided an example of wrapper code to
do serialization for a class that is not serializable, but would you provide an
example of how to transform a class that is not serializable directly into one
that is? I.e., not with a wrapper, but by adding implements Serializable and
then adding the explicit serialization methods to the class itself? I would
like to see an example of good Java programming with regard to serialization.
{quote}
The purpose of CM is to provide robust implementations of mathematical
utilities; supporting distributed applications is a totally different game.
{quote}
In my business, we often do massive calculations that require hundreds or
thousands of cpu-hours that need to be completed overnight, so they need to be
distributed. Regardless of how robust the implementation is otherwise, if it
does not support distribution, then that alone might make it unusable.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
https://issues.apache.org/jira/browse/MATH-742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13211195#comment-13211195
]
Neil Roeth commented on MATH-742:
-
{quote}
It was an example of a case where the appropriate serialization code might be
missing. In other words, because it is so simple to add Serializable just in
case, we create problems for later.
{quote}
I am not understanding what problems this could cause - can you give some
explicit examples? I don't know what your criteria are for appropriate
serialization code - can you describe a case where the default serialization
code is not appropriate and _why_ it is not appropriate?
As far as I can tell, the writeObject() and readObject() methods in
ExceptionContext are unnecessary because they simply do what the default
mechanism does anyway (except that it replaces throwing an exception for a
non-serializable object with a String that says it is non-serializable). What
am I missing?
Your code for a class that serializes PolynomialSplineFunction pulls
coefficients[] out of the underlying PolynomialFunction class and serializes
them. Why do that instead of just using PolynomialFunction.writeObject()? Why
is it better programming practice to create separate serialization classes that
have deep knowledge of the class structure of each of its data members rather
than encapsulate the serialization in each of those classes? If
PolynomialFunction implements Serializable, then either
PolynomialFunction.writeObject() will do the right thing or it is a bug in
PolynomialFunction's implementation of writeObject() - a serializer for
PolynomialSplineFunction shouldn't have to take on the responsibility of
serializing the guts of PolynomialFunction. I don't see how breaking
encapsulation like this is an improvement over the default mechanism, which
doesn't break it.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
--
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
https://issues.apache.org/jira/browse/MATH-742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=13209596#comment-13209596
]
Neil Roeth commented on MATH-742:
-
I'm kind of surprised at this result. One developer out of three objected, and
that's a consensus? That developer basically said this class should only be
Serialized if X, Y and Z were true. I responded that yes, indeed, it was
precisely X,Y and Z that were true and in fact were what led to my request.
I'd have thought that, all objections having been answered, it would have been
a done deal then. Particularly since PolynomialFunction, a class in the same
package, is already Serializable. Instead, Won't Fix? What objections were
raised that were not answered?
Luc, the work arounds you propose are poorer practice than using Serializable
exactly as it was intended. The work arounds both boil down to implement
serialization of PolynomialSplineFunction through home grown custom code
instead of simply adding the Java standard 'implements Serializable'. That is
not a better solution, so I am going to keep my locally customized version of
the class and hope you someday change your mind.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
--
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
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]
Neil Roeth commented on MATH-742:
-
Gilles,
In many cases, the default serialization mechanism is perfectly adequate, as in
this case where no one, not even the library maintainers, actually needs to do
anything nearly as complex as this code you supplied. Is there any possible
problem that adding implements Serializable in this one class could cause?
The only possible problem you raised is that someone, somewhere, might possibly
save this class as long term storage. How about you make this one class
Serializable, and if you get a bug report that it doesn't work when someone
uses it for long term storage, you just tell that person Don't do that?
Meanwhile, the rest of us can go ahead and use the Serializable class properly,
in exactly the circumstances that you stated serialization was for, i.e.,
passing data around in distributed processing.
There is no reason to saddle my simple, isolated issue with the burden of
proving that the Commons Math team must commit to making the whole library
Serializable. It doesn't have to commit to that. It is perfectly fine to make
only part of the library Serializable. The last time I checked, only part of
the Java API was Serializable. Just add implements Serializable to this
class. Then, put a big, bold statement on the web page that says, We made
some parts of Commons Math Serializable where it was trivial to do so, but we
do not plan at this time to tackle the parts that are not trivial. Patches to
do the latter are welcome, as long as they do it IN THE RIGHT WAY. Then
declare success and be happy that you made the library more useful.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
--
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
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]
Neil Roeth commented on MATH-742:
-
Luc, that is precisely my situation. I have a grid computing application where
my user-defined objects are returned from the grid, and they contain a
PolynomialSplineFunction that is a critical part of the calculated result.
Gilles, this is the plumbing needed for distributed applications in my case.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
--
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[jira] [Commented] (MATH-742) Please make PolynomialSplineFunction Serializable
[
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]
Neil Roeth commented on MATH-742:
-
Gilles,
{quote}The issue (and my question) is: Is this field needed in the
serialization?{quote}
Yes.
{quote}If it is needed, then again, is Serializable the correct way?{quote}
As you said, [Serializable] was meant to ease some of the plumbing needed for
distributed applications, so since my application is distributed and needs
this plumbing, the answer is again yes.
I raised this issue to add Serializable to this one particular class; if you
want to discuss globally adding Serializable to every class, that's a different
issue. Could you please open a new issue to discuss that topic? Thanks.
Please make PolynomialSplineFunction Serializable
-
Key: MATH-742
URL: https://issues.apache.org/jira/browse/MATH-742
Project: Commons Math
Issue Type: Improvement
Affects Versions: 2.2
Reporter: Neil Roeth
Priority: Minor
Attachments: PolynomialSplineFunction.java
PolynomialSplineFunction is not Serializable, while the very similar
PolynomialFunction class in the same package is. All that needs to be done is
to add the import:
{{import java.io.Serializable;}}
and change this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction}}
to this:
{{public class PolynomialSplineFunction implements
DifferentiableUnivariateRealFunction, Serializable}}
I made exactly that modification to a local copy and it serialized
successfully. Before the change, I got serialization errors.
Thanks.
--
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