forkjointask.java invokeall(t1,t2) method,this method source why not use double join() method?

Question

source:

public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
    t2.fork();
    t1.invoke();
    t2.join();
}

why not use :

public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
    t1.fork();
    t2.fork();
    t1.join();
    t2.join();
}

Answer 1

According to the documentation for ForkJoinTask :

Method invoke() is semantically equivalent to fork(); join() fork(); join() but always attempts to begin execution in the current thread.

So the version with invoke() is doing the same thing as your version, but instead of passing both jobs off to two different threads, it's passing t2 off to another thread and trying to handle t1 itself. That's less passing around, and less threads involved.

In your version, the current thread has nothing to do but wait once it fork() s both tasks.