src/main/java/io/reactivex/processors/MulticastProcessor.java
public boolean offer(T t) {
        if (once.get()) {
            return false;
        }
        ObjectHelper.requireNonNull(t, "offer called with null. Null values are generally not allowed in 2.x operators and sources.");
        if (fusionMode == QueueSubscription.NONE) {
            if (queue.offer(t)) {
                drain();
                return true;
            }
        }
        return false;
    }
public boolean offer(T t) {
        if (once.get()) {
            return false;
        }
        ObjectHelper.requireNonNull(t, "offer called with null. Null values are generally not allowed in 2.x operators and sources.");
        if (fusionMode == QueueSubscription.NONE) {
            if (queue.offer(t)) {
                drain();
                return true;
            }
        }
        return false;
    }
Tries to offer an item into the internal queue and returns false
if the queue is full.
@param t the item to offer, not null
@return true if successful, false if the queue is full