private void awaitInflightOperations() {
        try {
            while (globalInflightOperations.get() > 0) Thread.sleep(10);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
Same as {@link #feedMany(InputStream, ResultCallback)}, but without a provided {@link ResultCallback} instance.
@see JsonFeeder#feedMany(InputStream, ResultCallback) for details.
vespa-feed-client-api/src/main/java/ai/vespa/feed/client/JsonFeeder.java