/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * @test

 * @summary Check that appends are atomic

 */

import java.io.File;

import java.io.FileOutputStream;

import java.io.OutputStream;

import java.io.IOException;

import java.util.Random;

import java.util.concurrent.Executors;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.TimeUnit;

import java.nio.ByteBuffer;

import java.nio.channels.FileChannel;

import java.nio.file.Files;

import static java.nio.file.StandardOpenOption.*;

public class AtomicAppend {

    static final Random rand = new Random();

    // Open file for appending, returning FileChannel

    static FileChannel newFileChannel(File file) throws IOException {

        if (rand.nextBoolean()) {

            return new FileOutputStream(file, true).getChannel();

        } else {

            return FileChannel.open(file.toPath(), APPEND);

        }

    }

    // Open file for append, returning OutputStream

    static OutputStream newOutputStream(File file) throws IOException {

        if (rand.nextBoolean()) {

            return new FileOutputStream(file, true);

        } else {

            return Files.newOutputStream(file.toPath(), APPEND);

        }

    }

    // write a byte to the given channel

    static void write(FileChannel fc, int b) throws IOException {

        ByteBuffer buf = ByteBuffer.allocate(1);

        buf.put((byte)b);

        buf.flip();

        if (rand.nextBoolean()) {

            ByteBuffer[] bufs = new ByteBuffer[1];

            bufs[0] = buf;

            fc.write(bufs);

        } else {

            fc.write(buf);

        }

    }

    public static void main(String[] args) throws Throwable {

        final int nThreads = 16;

        final int writes = 1000;

        final File file = File.createTempFile("foo", null);

        try {

            ExecutorService pool = Executors.newFixedThreadPool(nThreads);

            for (int i = 0; i < nThreads; i++)

                pool.execute(new Runnable() { public void run() {

                    try {

                        // randomly choose FileChannel or OutputStream

                        if (rand.nextBoolean()) {

                            try (FileChannel fc = newFileChannel(file)) {

                                for (int j=0; j<writes; j++) write(fc, 'x');

                            }

                        } else {

                            try (OutputStream out = newOutputStream(file)) {

                                for (int j = 0; j<writes; j++) out.write('x');

                            }

                        }

                    } catch (IOException ioe) {

                        ioe.printStackTrace();

                    }

                }});

            pool.shutdown();

            pool.awaitTermination(1L, TimeUnit.MINUTES);

            if (file.length() != (long) (nThreads * writes))

                throw new RuntimeException("File not expected length");

        } finally {

            file.delete();

        }

    }

}