private void sync() throws InterruptedException {
            Future<?> sync;
            synchronized (monitor) {
                if (executor.isShutdown()) return;
                sync = executor.submit(() -> { });
            }
            try {
                sync.get();
            }
            catch (ExecutionException e) {
                throw new RuntimeException(e);
            }
        }
Oof, this is an attempt to see if there's a terminal bug in the Jetty client library that sometimes
renders a client instance permanently unusable. If this is the case, replacing the client altogether
should allow the feeder to start working again, when it wouldn't otherwise be able to.
vespa-feed-client/src/main/java/ai/vespa/feed/client/impl/HttpRequestStrategy.java