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  1. JDK
  2. JDK-8147505

BaseStream.onClose() should not allow registering new handlers after stream is consumed

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      Currently BaseStream.onClose() allows to register new handlers even after the stream is already consumed or even closed and they're actually executed on the consequtive close() call:

      Stream<String> s = Stream.of("content");
      s = s.onClose(() -> System.out.println("A"));
      s.forEach(System.out::println);
      s = s.onClose(() -> System.out.println("B"));
      s.close(); // prints A and B
      s = s.onClose(() -> System.out.println("C"));
      s.close(); // prints C

      The same result also produced when removing "s =":

      Stream<String> s = Stream.of("content");
      s.onClose(() -> System.out.println("A"));
      s.forEach(System.out::println);
      s.onClose(() -> System.out.println("B"));
      s.close(); // prints A and B
      s.onClose(() -> System.out.println("C"));
      s.close(); // prints C

      On the other hand, AutoCloseable interface (which BaseStream extends) encourages idempotent close() method. I propose the following change:

      * BaseStream.onClose() implementation (AbstractPipeline.onClose()) must throw IllegalStateException if the stream is already linked or consumed.
      * The documentation for BaseStream.onClose() should state that implementation may throw IllegalStateException if terminal operation is already called or stream is already closed.
      * BaseStream.close() implementation must do nothing if called the second time.

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            tvaleev Tagir Valeev
            tvaleev Tagir Valeev
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