Course of Raku / Functional, concurrent, reactive, and web programming / Concurrent programming / Threads

Starting a thread

Thread.start takes a block and runs it on a new thread, returning a Thread object that represents the running work:

my $t = Thread.start({ say 'hello from the thread' });

The block runs concurrently with the code that follows. The main program does not wait for it automatically — it continues immediately, and the thread does its work in the background.

One small but important detail: the argument must be a block of code. An empty pair of braces { } is an empty hash, not an empty block, so a thread always needs a body that actually does something:

my $t = Thread.start({ 2 + 2 }); # fine: a block with a body

Because the main program and the thread now run at the same time, you cannot rely on the order in which their output appears — unless you explicitly wait for the thread to finish, which is the subject of the next topic.

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