Hi Vanessa and Marcel,
Thank you for clarifying. Indeed, my notion of a recent image was a "current release" 5.3 image from a year and a half ago, which does not have the change, so I was indeed referring to primitive 72.
Sorry for the confusion,
Florin
On Tue, Jan 25, 2022 at 1:29 PM Vanessa Freudenberg vanessa@codefrau.net wrote:
@Florin,
I think nobody has mentioned yet that the behavior of Object>>becomeForward: in Squeak changed "recently".
What you were describing is the behavior of primitive 72, which indeed modified the argument's identity hash.
More recent Squeak releases use primitive 248 instead, which does not modify the target's hash. We also introduced primitive 249 which takes a boolean argument to indicate hash copying.
@Marcel: I think the comments might be more helpful if they explicitly mentioned which collections might have to be rehashed, and which (if any) object is being modified.
Vanessa
On Tue, Jan 25, 2022 at 03:44 Marcel Taeumel marcel.taeumel@hpi.de wrote:
Hi Florin --
it changes the identityHash of the argument, the non (obvious) target.
I updated the comment in #becomeForward: ... hope it helps:
"Primitive. All variables in the entire system that used to point to the receiver now point to the argument. Fails if either argument is an immediate such as a SmallInteger, or if the receiver is read-only. NOTE THAT the identityHash of the receiver IS NOT copied to the argument so that the argument should still be properly indexed in any existing hashed structures after the mutation. See #becomeForward:copyHash:."
Best, Marcel
Am 24.01.2022 15:11:09 schrieb Florin Mateoc florin.mateoc@gmail.com: Hi Clément and Marcel,
You are right, other use cases are supported, and there is probably no need for a separate setIdentityHash: primitive.
I guess I would not have minded if the method currently called #becomForward: would have been called #becomeForwardCopyHash: (plus a big, fat comment). As it is, it is not strictly a one way become method, it is a combination method instead, and its comment does not reflect that.
Best, Florin
On Mon, Jan 24, 2022 at 3:00 AM Marcel Taeumel wrote:
Hi Florin, hi Clément --
yes, that's what Squeak's #becomeForward:copyHash: is for.
See this discussion, where the interference between #becomeForward:,
copy
hash, and ModificationForbidden is explained:
http://lists.squeakfoundation.org/pipermail/squeak-dev/2020-April/208596.htm...
Best, Marcel
Am 24.01.2022 08:04:38 schrieb Clément Béra : Hi Florin,
I believe there are 2 primitives for 2 different use-cases:
- primitiveArrayBecomeOneWayNoCopyHash 248
- primitiveArrayBecomeOneWayCopyHash 249
The difference between both is which hash is preserved. I think for
your
use-case you should use the other primitive.
On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc wrote:
Hi,
I am a bit surprised by the #becomeForward: behavior in Squeak. This
is
a
one way become, where the target of the operation is the receiver,
which
sheds its identity/existence. Nobody points to it after the primitive execution, so it is discarded. This understanding also conforms to
the
method comment. As such, I remember a pattern of usage in VisualAge Smalltalk, where
one
way become was used as a cheap cleanup/avoidance of memory leaks, by
doing
oneWayBecome: nil. It's not that I advocate for it, but this works in Squeak too, except in Squeak #becomeForward: does an additional thing
to
the pointers redirection, it changes the identityHash of the
argument,
the
non (obvious) target. While I understand this may be useful in
certain
situations, I think it is a dangerous conflation of activities. A new primitive that sets the identity hash could be used (VA has it)
explicitly
instead when such behavior is desired. As it is, if I do "Object new becomeForward: nil", it succeeds and it changes nil's identityHash.
Sorry if this has been debated before,
Cheers, Florin
-- Clément Béra https://clementbera.github.io/ https://clementbera.wordpress.com/ Hi Florin,
I believe there are 2 primitives for 2 different use-cases:
- primitiveArrayBecomeOneWayNoCopyHash 248
- primitiveArrayBecomeOneWayCopyHash 249
The difference between both is which hash is preserved. I think for
your
use-case you should use the other primitive.
On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc wrote:
Hi,
I am a bit surprised by the #becomeForward: behavior in Squeak. This
is a
one way become, where the target of the operation is the receiver,
which
sheds its identity/existence. Nobody points to it after the primitive execution, so it is discarded. This understanding also conforms to the method comment. As such, I remember a pattern of usage in VisualAge Smalltalk, where
one
way become was used as a cheap cleanup/avoidance of memory leaks, by
doing
oneWayBecome: nil. It's not that I advocate for it, but this works in Squeak too, except in Squeak #becomeForward: does an additional thing
to
the pointers redirection, it changes the identityHash of the argument,
the
non (obvious) target. While I understand this may be useful in certain situations, I think it is a dangerous conflation of activities. A new primitive that sets the identity hash could be used (VA has it)
explicitly
instead
when such behavior is desired. As it is, if I do "Object new becomeForward: nil", it succeeds and it changes nil's identityHash.
Sorry if this has been debated before,
Cheers, Florin
-- Clément Béra https://clementbera.github.io/ https://clementbera.wordpress.com/
Hi Clément and Marcel,
You are right, other use cases are supported, and there is probably no need for a separate setIdentityHash: primitive.
I guess I would not have minded if the method currently called #becomForward: would have been called #becomeForwardCopyHash: (plus a big, fat comment). As it is, it is not strictly a one way become method, it is a combination method instead, and its comment does not reflect that.
Best, Florin
On Mon, Jan 24, 2022 at 3:00 AM Marcel Taeumel marcel.taeumel@hpi.de wrote:
Hi Florin, hi Clément --
yes, that's what Squeak's #becomeForward:copyHash: is for.
See this discussion, where the interference between #becomeForward:, copy hash, and ModificationForbidden is explained:
http://lists.squeakfoundation.org/pipermail/squeak-dev/2020-April/208596.htm...
Best, Marcel
Am 24.01.2022 08:04:38 schrieb Clément Béra bera.clement@gmail.com: Hi Florin,
I believe there are 2 primitives for 2 different use-cases:
primitiveArrayBecomeOneWayNoCopyHash 248
primitiveArrayBecomeOneWayCopyHash 249
The difference between both is which hash is preserved. I think for your
use-case you should use the other primitive.
On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc
wrote:
Hi,
I am a bit surprised by the #becomeForward: behavior in Squeak. This
is a
one way become, where the target of the operation is the receiver,
which
sheds its identity/existence. Nobody points to it after the primitive
execution, so it is discarded. This understanding also conforms to the
method comment.
As such, I remember a pattern of usage in VisualAge Smalltalk, where
one
way become was used as a cheap cleanup/avoidance of memory leaks, by
doing
oneWayBecome: nil. It's not that I advocate for it, but this works in
Squeak too, except in Squeak #becomeForward: does an additional thing
to
the pointers redirection, it changes the identityHash of the argument,
the
non (obvious) target. While I understand this may be useful in certain
situations, I think it is a dangerous conflation of activities. A new
primitive that sets the identity hash could be used (VA has it)
explicitly
instead when such behavior is desired.
As it is, if I do "Object new becomeForward: nil", it succeeds and it
changes nil's identityHash.
Sorry if this has been debated before,
Cheers,
Florin
--
Clément Béra
https://clementbera.github.io/
https://clementbera.wordpress.com/
Hi Florin,
I believe there are 2 primitives for 2 different use-cases:
- primitiveArrayBecomeOneWayNoCopyHash 248
- primitiveArrayBecomeOneWayCopyHash 249
The difference between both is which hash is preserved. I think for your use-case you should use the other primitive.
On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc florin.mateoc@gmail.com wrote:
Hi,
I am a bit surprised by the #becomeForward: behavior in Squeak. This is a one way become, where the target of the operation is the receiver, which sheds its identity/existence. Nobody points to it after the primitive execution, so it is discarded. This understanding also conforms to the method comment. As such, I remember a pattern of usage in VisualAge Smalltalk, where one way become was used as a cheap cleanup/avoidance of memory leaks, by doing oneWayBecome: nil. It's not that I advocate for it, but this works in Squeak too, except in Squeak #becomeForward: does an additional thing to the pointers redirection, it changes the identityHash of the argument, the non (obvious) target. While I understand this may be useful in certain situations, I think it is a dangerous conflation of activities. A new primitive that sets the identity hash could be used (VA has it) explicitly
instead
when such behavior is desired. As it is, if I do "Object new becomeForward: nil", it succeeds and it changes nil's identityHash.
Sorry if this has been debated before,
Cheers, Florin
-- Clément Béra https://clementbera.github.io/ https://clementbera.wordpress.com/