Question about using select in loops

[ytoh]

Hi team!

I am enjoying the results of the work you have done on this library. Thank you for it. I have one question. I am trying to drain multiple channels into one and when I use Select#selectOrClosed in a loop I encounter a situation that from the point a single channel gets closed I only ever get a ChannelDone out. The following is the behavior captured in a unit test.

  @Test
  void test_only_done() throws InterruptedException {
    var ch1 = new Channel<String>(1);
    var ch2 = new Channel<String>(1);
    ch1.done();
    ch2.send("hello");
    ch2.done();

    for (int i = 0; i < 100; i++) {
      var result = Select.selectOrClosed(ch1.receiveClause(), ch2.receiveClause());
      assertInstanceOf(ChannelDone.class, result);
    }
  }

If I want to avoid this problem I have to remove closed channels from the list being selected on every iteration. I captured this in a unit test as well:

@Test
  void test_select_with_remove() throws InterruptedException {
    var ch1 = new Channel<String>(1);
    var ch2 = new Channel<String>(1);
    var output = new Channel<String>(2);
    ch1.done();
    ch2.send("hello");
    ch2.done();

    var receiveClauses = Stream.of(ch1, ch2).map(Channel::receiveClause).toList();
    do {
      var o = Select.selectOrClosed(receiveClauses.toArray(new SelectClause[0]));
      if (!(o instanceof ChannelDone)) {
        output.send((String) o);
      }
      receiveClauses =
          Stream.of(ch1, ch2)
              .filter(ch -> !ch.isClosedForReceive())
              .map(Channel::receiveClause)
              .toList();
    } while (!receiveClauses.isEmpty());
    output.done();

    assertEquals("hello", output.receive());
    assertInstanceOf(ChannelDone.class, output.receiveOrClosed());
  }

I have to loop through all of the channels because unfortunately the ChannelDone signal does not have a reference to the channel that it relates to :(.

My question is: Is this the correct behavior or am I doing something silly?
Thanks!

[adamw]

Yes, it's a shortcoming I'm hoping to address sooner rather than later :) That's how we're using channels too (filtering out the "done" ones if needed)

[adamw]

related: softwaremill/ox#201