protected final void failInOtherThread(
                final CompletionHandler handler,
                final Throwable failure,
                final Class<?>... allowedExceptionTypes) {
            callInOtherThread(() -> {
                fail(handler, failure, allowedExceptionTypes);
                return null;
            });
        }
Wrapper around CountDownLatch for single-occurrence events.
jdisc_core/src/main/java/com/yahoo/jdisc/test/ServerProviderConformanceTest.java