The Self command returns the threads identifier of the current thread.

For the main thread, the thread identifier is always 0.  For other threads, the thread identifier is an integer greater than 0.

$\mathrm{id}≔\mathrm{Threads}:-\mathrm{Create}\left(\mathrm{print}\left(\mathrm{Threads}:-\mathrm{Self}\left(\right)\right)\right)$

$\mathrm{id}≔1$

$\mathrm{Threads}:-\mathrm{Wait}\left(\mathrm{id}\right)$

$n≔5$

$n≔5$

t := table();
p := proc( t )
    t[ Threads:-Self() ] := 1;
end proc;

$t≔table\left(\left[\right]\right)$

$p≔\mathbf{proc}\left(t\right)t\[\mathrm{Threads}:-\mathrm{Self}\left(\right)\]≔1\mathbf{end\; proc}$

$s≔\left[\mathrm{seq}\left(\mathrm{Threads}:-\mathrm{Create}\left(p\left(t\right)\right)\,i=1..n\right)\right]$

$s≔\left[2\,3\,4\,5\,6\right]$

$\mathrm{Threads}:-\mathrm{Wait}\left(\mathrm{op}\left(s\right)\right)$

$\mathrm{indices}\left(t\right)$

$\left[2\right],\left[3\right],\left[4\right],\left[5\right],\left[6\right]$