[concurrency-interest] draft Carrier API

[Doug Lea]

On 3/9/20 3:29 PM, Alex Otenko wrote:
> IllegalStateException is ok if receiver should've known there are no
> more items to receive. This is a good idea in cases with definite length
> of stream, and the length being known to the receiver before entering
> receive(). This doesn't seem like a good idea for indefinite length
> cases - like, loop to read all items until eof.
> 
This is the reason for:
    Stream<T> stream();             // destructive (consume-on-traverse)
But it is also sensible to provide a simpler forEach analog:
    long consumeEach(Consumer<? super T> proc); // return count

For those who need stateful loops, we could add "eventually" forms of
tryReceive. With non-value-types, the preferable form that can co-exist
with value-types is usually to return a resultIfAbsent (that is almost
always chosen to be null), and for value types, Optional. To avoid
annoying people, we should probably have both.

    T tryReceive(T resultIfAbsent); // resultIfAbsent if closed or empty
    Optional<T> tryReceive();       // Optional.empty if closed or empty

    T tryReceiveEventually(T resultIfAbsent); // resultIfAbsent if closed
    Optional<T> tryReceiveEventually(); // Optional.empty if closed

Maybe there is a better method name.

(See updates at http://gee.cs.oswego.edu/dl/wwwtmp/Carrier.java)

-Doug