/** @return {@code true} if entered to busy state. */
private boolean enterBusy() {
if (busyLock.readLock().tryLock()) return true;
if (log.isDebugEnabled())
log.debug("Failed to enter busy state (exchanger is stopping): " + this);
return false;
}
private void leaveBusy() {
busyLock.readLock().unlock();
}
