private void retryForever(Runnable command) {
        while (true) {
            try {
                primary.execute(command);
                return;
            } catch (RejectedExecutionException rejected) {
                try {
                    Thread.sleep(1);
                } catch (InterruptedException silenced) { }
            }
        }
    }
An executor that will first try a bounded cached thread pool before falling back to an unbounded
single threaded thread pool that will take over dispatching to the primary pool.
vespajlib/src/main/java/com/yahoo/concurrent/CachedThreadPoolWithFallback.java