8334719: (se) Deferred close of SelectableChannel may result in a Selector doing the final close before concurrent I/O on channel has completed

Co-authored-by: Alan Bateman <alanb@openjdk.org>
Reviewed-by: alanb, dfuchs

src/java.base/share/classes/sun/nio/ch/ServerSocketChannelImpl.java

@@ -654,6 +654,9 @@ class ServerSocketChannelImpl
 
     @Override
     public void kill() {
+        // wait for any accept operation to complete before trying to close
+        acceptLock.lock();
+        acceptLock.unlock();
         synchronized (stateLock) {
             if (state == ST_CLOSING) {
                 tryFinishClose();