I'm not familiar enough with the "inner workings" of Perl to play around with "passing around control of filehandles". However, I rarely ever see this done, and to do it with threads adds another layer of complexity. I think you may be forging new territory/. :-)

My first thought is to forget about passing "filhandles" and to pass the "files saved in scalar variables" through the cond_broadcast facility in threads. I'm not too quick to whip off example code, but what I mean is to figure out how to pass scalars around between threads. Alot of examples have been posted how to do this. Then in each thread, use the "variable as a filehandle technique" like:

my $foo = '';
open FILEHANDLE, '+>', \$foo or die $!;
print FILEHANDLE "Contents of File";
seek(FILEHANDLE,0,0);
my @contents = <FILEHANDLE>;
close FILEHANDLE or die $!;
print 'From $foo: ', $foo, $/;
print 'From file read: ', @contents, $/;
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Now, in each thread, you can open and close on that variable, then "broadcast it" to the other threads where they can do the same thing.