"Tid" is the thread id which is unique and is given to each thread
thread->list returns a list of thread objects, one for each thread that's currently running

foreach my $thr (threads->list()) {
         ##DO something 
        }
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Read Threads for more information, it's not best but you can refer it for list purpose.
Update:
<$thr->is_running()
Returns true if a thread is still running (i.e., if its entry point function has not yet finished or exited).
$thr->is_joinable()
Returns true if the thread has finished running, is not detached and has not yet been joined.
In other words, the thread is ready to be joined, and a call to $thr->join() will not block.
threads->list()
threads->list(threads::all)
threads->list(threads::running)
threads->list(threads::joinable)
With no arguments (or using threads::all ) and in a list context, returns a list of all non-joined,
non-detached threads objects. In a scalar context, returns a count of the same.
With a true argument (using threads::running ), returns a list of all non-joined,
non-detached threads objects that are still running.
With a false argument (using threads::joinable ), returns a list of all non-joined, non-detached
threads objects that have finished running (i.e., for which ->join() will not block).