private void writeAll(final ContentChannel out, final Iterable<ByteBuffer> content) {
            for (ByteBuffer buf : content) {
                out.write(buf, newCompletionHandler());
            }
        }
Wrapper around CountDownLatch for single-occurrence events.
jdisc_core/src/main/java/com/yahoo/jdisc/test/ServerProviderConformanceTest.java