code: static int bestEffortMaxSubscribers(ExecutorService executor) {
  		int maxSubscribers = Integer.MIN_VALUE;
  		if (executor instanceof ThreadPoolExecutor) {
  			maxSubscribers = ((ThreadPoolExecutor) executor).getMaximumPoolSize();
  		}
  		else if (executor instanceof ForkJoinPool) {
  			maxSubscribers = ((ForkJoinPool) executor).getParallelism();
  		}
  		return maxSubscribers;
  	}
docs: This method will attempt to compute the maximum amount of subscribers a
  {@link WorkQueueProcessor} can accommodate based on a given {@link ExecutorService}.
  <p>
  It can only accurately detect this for {@link ThreadPoolExecutor} and
  {@link ForkJoinPool} instances, and will return {@link Integer#MIN_VALUE} for other
  executor implementations.
  
  @param executor the executor to attempt to introspect.
  @return the maximum number of subscribers the executor can accommodate if it can
  be computed, or {@link Integer#MIN_VALUE} if it cannot be determined.