In which case I want to capture STDOUT and STDERR of each worker "process".

And there is the source of my question: Why are you quoting "process"?

Either this is

1. a real separate process;

   In which case you need to 'capture' the output from STDOUT and STDERR.

2. Or it is just perl code running in a thread; and using the term 'process' is just misleading.

   In this case you don't need to 'capture' the output; you simply need to direct it to where you want it to go.

   Ie. If you are going to call a subroutine that normally writes to stdout and stderr; and you want that output to end up in a file of your choosing, then point stdout and stderr to that file before you call the subroutine:

   sub worker {
       local( *STDOUT, *STDERR );
       open STDOUT, '>', 'my.log' or die $!;
       open STDERR, '>&STDOUT' or die $!;
       unmodifiable(); ## call the code that produces the output; it'll e
   +nd up in my.log
       ## the effects of the redirection get cleaned up automatically whe
   +n the worker ends.
   }
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