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Author Mark.Shannon
Recipients Mark.Shannon, carljm, corona10, dino.viehland, eelizondo, gregory.p.smith, nascheme, pablogsal, pitrou, shihai1991, steve.dower, tim.peters, vstinner
Date 2020-04-16.12:15:10
SpamBayes Score -1.0
Marked as misclassified Yes
Message-id <>
A big -1 to this.

You are asking the whole world to take a hit on both performance and memory use, in order to save Instagram memory.

The PR uses the term "immortal" everywhere. There is only one reference to copy-on-write in a comment. Yet this issue about making object headers immutable.
Immortality and object header immutability are not the same.

If object header immutability is to be a requirement, that needs a PEP.

If it is not requirement, but immortality is, then make the obvious improvement of changing the branchy code

if (!(obj->refcnt & IMMORTAL_BIT)) {

to the branchless

obj->refcnt += ((obj->refcnt &IMMORTAL_BIT) != 0)

Immortality has advantages because it allows saturating reference counting and thus smaller object headers, but it is not the same as making the object header immutable.
Date User Action Args
2020-04-16 12:15:11Mark.Shannonsetrecipients: + Mark.Shannon, tim.peters, nascheme, gregory.p.smith, pitrou, vstinner, carljm, dino.viehland, steve.dower, corona10, pablogsal, eelizondo, shihai1991
2020-04-16 12:15:11Mark.Shannonsetmessageid: <>
2020-04-16 12:15:11Mark.Shannonlinkissue40255 messages
2020-04-16 12:15:10Mark.Shannoncreate