Understanding invokeAll method of the ForkJoinTask

Question

While I was reading the javadoc about ForkJoinTask I came across the following statement:

This method may be invoked only from within ForkJoinPool computations (as may be determined using method inForkJoinPool()). Attempts to invoke in other contexts result in exceptions or errors, possibly including ClassCastException.

What's not clear to me is what ForkJoinContext means here. I know what static context means, for example. It clearly defines in the JLS 8.1.3 as follows (Emphasize's mine):

A statement or expression occurs in a static context if and only if the innermost method, constructor, instance initializer, static initializer, field initializer, or explicit constructor invocation statement enclosing the statement or expression is a static method, a static initializer, the variable initializer of a static variable, or an explicit constructor invocation statement (§8.8.7).

Answer 1

The context being discussed here is not static/non-static context.

It means that the method must be called from a thread which belongs to the ForkJoinPool.

So it must be called from a recursive task. Calling from anywhere else might cause exceptions/errors.