In Perl 6, there is the Thread class, which takes care of creating and running threads. To see in which thread you are at the moment, use the $*THREAD pseudo constant:
say $*THREAD;
It returns a value of the Thread class, and the default stringified representation of it is a string containing the identifier and the name of the thread:
Thread #1 (Initial thread)
Don't rely on the particular value of the thread identifier as it may be different even for the main thread.