public void awaitTermination(final Timeout timeout) throws InterruptedException {
        thread.join(timeout != null ? timeout.toMilliseconds() : Long.MAX_VALUE);
    }
This class maintains a background thread to enforce an eviction policy for expired / idle
persistent connections kept alive in the connection pool.

@since 4.4
httpclient5/src/main/java/org/apache/hc/client5/http/impl/IdleConnectionEvictor.java