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Re: Robin Hood Hashing for the perl core

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From:
Ed Avis
Date:
August 22, 2021 03:40
Subject:
Re: Robin Hood Hashing for the perl core
Message ID:
DM4PR11MB5247B3ACD40A6D87494D0ED19DC19@DM4PR11MB5247.namprd11.prod.outlook.com
Tony Cook wrote:

>In addition to Nicholas's response, when objects are duplicated into a
>new thread the duplicated object has a new address which breaks
>the hash, and finding the object given the address.

But that's equally true with the way hashing works currently.  The address changes, so the string representation changes, so you can no longer look up with the same key.

% perl -Mthreads -le 'my $x = bless {}; $h{$x} = "hello"; print $h{$x}; threads->create(sub { print $h{$x} // "undef" })->join'
hello
undef

So while it's a reminder to be careful about object identity when you are using threads, it's not a point of difference between stringifying hash keys and hashing by address.


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