Returns the first (longest-waiting) thread in the queue, or
{@code null} if no threads are currently queued.
<p>In this implementation, this operation normally returns in
constant time, but may iterate upon contention if other threads are
concurrently modifying the queue.
@return the first (longest-waiting) thread in the queue, or
{@code null} if no threads are currently queued
Returns the first (longest-waiting) thread in the queue, or {@code null} if no threads are currently queued.
<p>In this implementation, this operation normally returns in constant time, but may iterate upon contention if other threads are concurrently modifying the queue.
@return the first (longest-waiting) thread in the queue, or {@code null} if no threads are currently queued