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This is because they copy every data structure except the ones you mark as shared

Only if the data structures exist before the threads are spawned. So don't do that. Spawn your threads before you load or create your large data structures. It ain't rocket science.

And, as has been mentioned before, most forked perl processes do not benefit from COW much either:

  • If you take a reference, the data is modified and therefore copied.
  • If you bless or re-bless the data, magic is added and it get copied.
  • If you perform math on data that was loaded as text, it gets converted to numeric representation, therefore is modified, and hence copied.
  • Interpolate a numeric scalar into a string, it gets copied.
  • int a real or string value, it gets copied.
  • chomp a scalar, it gets copied.
  • study a scalar, it gets copied.
  • Change a variable from readonly to readwrite, it gets copied.
  • Iterate a hash, or reset the iterator, stuff gets copied.
  • Even just searching a scalar could cause the Boyer Moore tables to be generated.

And that's just a few of the apparently read-only operations that will cause COW to trigger. Doing anything non-readonly, like adding or deleting an element to a hash or array and you induce wholesale copying. Increment or decrement a variable. Modify it 'in-place' with s/// or tr or substr.


Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^2: Perl Threads and multi-core CPUs by BrowserUk
in thread Perl Threads and multi-core CPUs by haidut

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