Foo.java

package wtf.g4s8.qabot;

import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.channels.CompletionHandler;
import java.nio.file.Paths;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import static java.nio.file.StandardOpenOption.*;

/**
 *
 * @since
 */
public final class Foo {

    private static final int BUF_SIZE = 1024 * 1024 * 1024;

    public static void main(String[] args) throws Exception {
        final var f1 = Paths.get("/tmp/foo/1.txt");
        final var f2 = Paths.get("/tmp/foo/2.txt");
        final var f3 = Paths.get("/tmp/foo/3.txt");
        final var inc = new AtomicInteger(1);
        final var exec = Executors.newSingleThreadExecutor(
            new ThreadFactory() {
                @Override
                public Thread newThread(final Runnable r) {
                    final var thread = new Thread(r);
                    thread.setName(String.format("io-%d", inc.incrementAndGet()));
                    return thread;
                }
            }
        );
        final ByteBuffer b1 = newBuff(BUF_SIZE);
        final ByteBuffer b2 = newBuff(BUF_SIZE);
        final ByteBuffer b3 = newBuff(BUF_SIZE);
        final var chan1 = AsynchronousFileChannel.open(f1, new HashSet<>(List.of(READ, WRITE, CREATE)), exec);
        final var chan2 = AsynchronousFileChannel.open(f2, new HashSet<>(List.of(READ, WRITE, CREATE)), exec);
        final var chan3 = AsynchronousFileChannel.open(f3, new HashSet<>(List.of(READ, WRITE, CREATE)), exec);
        final long start = System.nanoTime();
        final var ch1complete = new AtomicBoolean();
        final var ch2complete = new AtomicBoolean();
        final var ch3complete = new AtomicBoolean();
        chan1.write(b1, 0, null, new CompletionHandler<Integer, Void>() {
            @Override
            public void completed(final Integer result, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan1 completed in %d (ms)\n", (start - end) / 1_000_000);
                ch1complete.set(true);
            }

            @Override
            public void failed(final Throwable exc, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan1 failed in %d (ms): %s\n", (start - end) / 1_000_000, exc);
                ch1complete.set(true);
            }
        });
        chan2.write(b2, 0, null, new CompletionHandler<Integer, Void>() {
            @Override
            public void completed(final Integer result, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan2 completed in %d (ms)\n", (start - end) / 1_000_000);
                ch2complete.set(true);
            }

            @Override
            public void failed(final Throwable exc, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan2 failed in %d (ms): %s\n", (start - end) / 1_000_000, exc);
                ch2complete.set(true);
            }
        });
        chan3.write(b3, 0, null, new CompletionHandler<Integer, Void>() {
            @Override
            public void completed(final Integer result, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan3 completed in %d (ms)\n", (start - end) / 1_000_000);
                ch3complete.set(true);
            }

            @Override
            public void failed(final Throwable exc, final Void attachment) {
                final long end = System.nanoTime();
                System.out.printf("chan3 failed in %d (ms): %s\n", (start - end) / 1_000_000, exc);
                ch3complete.set(true);
            }
        });
        Thread.sleep(10);
        exec.submit(() -> {
            final var end = System.nanoTime();
            System.out.printf("print: %d\n", (start - end) / 1_000_000);
        });
        while (!Thread.currentThread().isInterrupted()) {
            if (ch1complete.get() && ch2complete.get() && ch3complete.get()) {
                final long end = System.nanoTime();
                System.out.printf("both channels completed in %d (ms)\n", (start - end) / 1_000_000);
                return;
            }
        }
    }

    private static ByteBuffer newBuff(int size) {
        final var buf = ByteBuffer.allocate(size);
        return buf;
    }
}