In which thread does CompletableFuture's completion handlers execute in?

Question

I have a question about CompletableFuture method:

public  CompletableFuture thenApply(Function fn)
         


        

Answer 1

From the Javadoc:

Actions supplied for dependent completions of non-async methods may be performed by the thread that completes the current CompletableFuture, or by any other caller of a completion method.

More concretely:

• fn will run during the call to complete() in the context of whichever thread has called complete().

• If complete() has already finished by the time thenApply() is called, fn will be run in the context of the thread calling thenApply().