reactor-core/src/main/java/reactor/core/publisher/WorkQueueProcessor.java
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;
	}
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;
	}
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.