@Override
                    public void close(CompletionHandler handler) {
                        try {
                            requestContentChannel.close(handler);
                        } finally {
                            removeTask(requestContentChannelCloseTask);
                        }
                    }
Wrapper around CountDownLatch for single-occurrence events.
jdisc_core/src/main/java/com/yahoo/jdisc/test/ServerProviderConformanceTest.java