reactor-core/src/main/java/reactor/core/publisher/Operators.java
public static <T> long addCap(AtomicLongFieldUpdater<T> updater, T instance, long toAdd) {
		long r, u;
		for (;;) {
			r = updater.get(instance);
			if (r == Long.MAX_VALUE) {
				return Long.MAX_VALUE;
			}
			u = addCap(r, toAdd);
			if (updater.compareAndSet(instance, r, u)) {
				return r;
			}
		}
	}
public static <T> long addCap(AtomicLongFieldUpdater<T> updater, T instance, long toAdd) {
		long r, u;
		for (;;) {
			r = updater.get(instance);
			if (r == Long.MAX_VALUE) {
				return Long.MAX_VALUE;
			}
			u = addCap(r, toAdd);
			if (updater.compareAndSet(instance, r, u)) {
				return r;
			}
		}
	}
Concurrent addition bound to Long.MAX_VALUE.
Any concurrent write will "happen before" this operation.

@param <T> the parent instance type
@param updater  current field updater
@param instance current instance to update
@param toAdd    delta to add
@return value before addition or Long.MAX_VALUE