test/jdk/java/nio/channels/Selector/HelperSlowToDie.java

/*
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/*
 * @test
 * @bug 6823609
 * @summary Selector.select can hangs on Windows for cases where a helper thread
 *   becomes redudant but a new helper is immediately needed.
 * @requires (os.family == "windows")
 */

import java.nio.channels.*;
import java.io.IOException;

public class HelperSlowToDie {
    private static final int CHANNELS_PER_THREAD = 1023;
    private static final int TEST_ITERATIONS = 200;
    private static volatile boolean done;

    public static void main(String[] args) throws IOException {
        Selector sel = Selector.open();

        // register channels
        SocketChannel[] channels = new SocketChannel[CHANNELS_PER_THREAD];
        for (int i=0; i<CHANNELS_PER_THREAD; i++) {
            SocketChannel sc = SocketChannel.open();
            sc.configureBlocking(false);
            sc.register(sel, SelectionKey.OP_CONNECT);
            channels[i] = sc;
        }
        sel.selectNow();

        // Start threads to swamp all cores but one. This improves the chances
        // of duplicating the bug.
        Runnable busy = new Runnable() {
            public void run() {
                while (!done) ;  // no nothing
            }
        };
        int ncores = Runtime.getRuntime().availableProcessors();
        for (int i=0; i<ncores-1; i++)
            new Thread(busy).start();

        // Loop changing the number of channels from 1023 to 1024 and back.
        for (int i=0; i<TEST_ITERATIONS; i++) {
            SocketChannel sc = SocketChannel.open();
            sc.configureBlocking(false);
            sc.register(sel, SelectionKey.OP_CONNECT);
            sel.selectNow();   // cause helper to spin up
            sc.close();
            sel.selectNow();  // cause helper to retire
        }

        // terminate busy threads
        done = true;

        // clean-up
        for (int i=0; i<CHANNELS_PER_THREAD; i++) {
            channels[i].close();
        }
        sel.close();
    }
}