The behavior is similar with the forks module.

use strict;
use warnings;
use forks;

sub worker
{
    print "Worker thread started.\n";
    while(1){}
}

my $proc = threads->create(\&worker);

print "Setting alarm.\n";
$SIG{ALRM} = sub { print "Alarm!\n" };
alarm 2;

print "Joining.\n";
$proc->join();
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Output

Setting alarm.
Joining.
Worker thread started.
Alarm!
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Kind regards, Mario.