> On 16 Feb 2015, at 23:32, Nicolai Hess <[hidden email]> wrote:
>
> 2015-02-05 16:02 GMT+01:00 Sven Van Caekenberghe <[hidden email]>:
>
> > On 05 Feb 2015, at 15:44, Nicolai Hess <[hidden email]> wrote:
> >
> > 2015-02-02 3:03 GMT+01:00 Eliot Miranda <[hidden email]>:
> >
> >
> > On Sun, Feb 1, 2015 at 3:39 AM, Nicolai Hess <[hidden email]> wrote:
> >
> >
> > 2015-02-01 10:52 GMT+01:00 Ben Coman <[hidden email]>:
> >
> > Looking into Image locking problems [1] caused by a recursive array such as this...
> >
> >     literalArray := #( 1 2 3 ).
> >     literalArray at: 3 put: literalArray.
> >
> > I find that "literalArray printString" locks the image due to Array>>printOn: use of the recursive #shouldBePrintedAsLiteral method. Now its implementation is identical to #isLiteral and indeed "literalArray isLiteral" also locks the Image. So comparing implementors of #isLiteral...
> >
> >
> >
> > Squeak uses a Set to store all visited elements for shouldBePrintedAsLiteral and this protects against the recursive loop.
> >
> > shouldBePrintedAsLiteralVisiting: aSet
> >     self class == Array ifFalse:
> >         [^false].
> >     (aSet includes: self) ifTrue:
> >         [^false].
> >     aSet add: self.
> >     ^self allSatisfy: [:each | each shouldBePrintedAsLiteralVisiting: aSet]
> >
> >
> > isn't there a common pattern to handle this kind of potential endless recursion?
> >
> > At Cadence we fixed it thus:
> >
> > Object>>shouldBePrintedAsLiteral
> >
> >       ^self isLiteral
> >
> > Array>>shouldBePrintedAsLiteral
> >
> >       ^self class == Array
> >         and: [self shouldBePrintedAsLiteralVisiting: (IdentitySet new: 8)]
> >
> > Object>>shouldBePrintedAsLiteralVisiting: aSet
> >
> >       ^self isLiteral
> >
> >  Array>>shouldBePrintedAsLiteralVisiting: aSet
> >       self class == Array ifFalse:
> >               [^false].
> >       (aSet includes: self) ifTrue:
> >               [^false].
> >       aSet add: self.
> >       ^self allSatisfy: [:each | each shouldBePrintedAsLiteralVisiting: aSet]
> >
> >
> > Is there something more "generic". Something we can use for any object tracing.
> > Isn't there something the GC uses? The GC obviously does not fall into this loop.
> > (It flags visited objects, but there is nothing exposed that can be used
> > at the image level?)
> > How do ImageSegment or Fuel work with recursive structures?
>
> In Moose there is DeepTraverser which does something similar it seems.
>
> FUEL & STON do this too.
>
> How is it done in Fuel and STON ? Do they both use DeepTraverser, or
> is there another implementation in Fuel and another one in STON?

They both have their own implementation. The actual traversal is not that difficult, doing it efficiently is a bit harder. Getting all the edge cases of the total algorithm (the serialisation) right is a more work.

I am not familiar with DeepTraverser, I just know it exists.

> > Nicolai
> >
> >
> >
> >   Object>>isLiteral           ^false
> >   Boolean>>isLiteral          ^true
> >   Character>>isLiteral                ^true
> >   Integer>>isLiteral          ^true
> >   String>>isLiteral           ^true
> >   UndefinedObject>>isLiteral  ^true
> >
> >   ByteArray>>isLiteral                ^self class == ByteArray
> >   Float>>isLiteral            ^self isFinite "^(self - self) = 0.0"
> >   ScaledDecimal>>isLiteral    ^denominator = 1 or: [(10 raisedTo: scale)\\denominator = 0]
> >
> >   Array>>isLiteral            ^self class == Array and: [self allSatisfy: [:each | each isLiteral]]
> >
> > ...I find most are very basic (might even say deterministic), with the recursion of Array>>isLiteral seeming an annomaly.  Also, the big IF condition in Array>>printOn: smells like a design decision being made at runtime (Valloud AMCOS p12).
> >
> >     Array>>printOn: aStream
> >       self shouldBePrintedAsLiteral ifTrue: [self printAsLiteralFormOn: aStream. ^ self].
> >       self isSelfEvaluating ifTrue: [self printAsSelfEvaluatingFormOn: aStream. ^ self].
> >       super printOn: aStream
> >
> > Flipping between two printString formats seems like selecting between two class types. Indeed, if we had a LiteralArray class, there would be no need for its printOn: to recursively search to determine its form, thus allowing #printStringLimitedTo: to do its thing to protect against infinite recursion.
> >
> > Also, instead of a recursive Array>>isLiteral we'd have something like
> >   LiteralArray>>isLiteral     ^true
> >   Array>>isLiteral            ^false
> > which seems to align much better with the pattern of the other #isLiteral implementors.
> >
> > I notice there is both RBArrayNode and RBLiteralArrayNode.
> >
> > So what are the wider concerns that might apply?
> > (In particular, I'm not sure how the #isSelfEvaluating (which is also recursive) fits into the big picture)
> >
> > cheers -ben
> >
> > [1] https://www.mail-archive.com/pharo-dev@.../msg25156.html
> >
> >
> >
> >
> > --
> > best,
> > Eliot