/*

 * Copyright 2009 Google Inc.  All Rights Reserved.

 * 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.

 *

 */

import java.util.*;

import java.io.*;

/**

 * A manual test that demonstrates the ability to start a subprocess

 * on Linux without getting ENOMEM.  Run this test like:

 *

 * java -Xmx7000m BigFork

 *

 * providing a -Xmx flag suitable for your operating environment.

 * Here's the bad old behavior:

 *

 * ==> java -Xmx7000m -esa -ea BigFork

 * -------

 * CommitLimit:   6214700 kB

 * Committed_AS:  2484452 kB

 * -------

 * size=4.6GB

 * -------

 * CommitLimit:   6214700 kB

 * Committed_AS:  7219680 kB

 * -------

 * Exception in thread "main" java.io.IOException: Cannot run program "/bin/true": java.io.IOException: error=12, Cannot allocate memory

 *         at java.lang.ProcessBuilder.start(ProcessBuilder.java:1018)

 *         at BigFork.main(BigFork.java:79)

 * Caused by: java.io.IOException: java.io.IOException: error=12, Cannot allocate memory

 *         at java.lang.UNIXProcess.<init>(UNIXProcess.java:190)

 *         at java.lang.ProcessImpl.start(ProcessImpl.java:128)

 *         at java.lang.ProcessBuilder.start(ProcessBuilder.java:1010)

 *         ... 1 more

 */

public class BigFork {

    static final Random rnd = new Random();

    static void touchPages(byte[] chunk) {

        final int pageSize = 4096;

        for (int i = 0; i < chunk.length; i+= pageSize) {

            chunk[i] = (byte) rnd.nextInt();

        }

    }

    static void showCommittedMemory() throws IOException {

        BufferedReader r =

            new BufferedReader(

                new InputStreamReader(

                    new FileInputStream("/proc/meminfo")));

        System.out.println("-------");

        String line;

        while ((line = r.readLine()) != null) {

            if (line.startsWith("Commit")) {

                System.out.printf("%s%n", line);

            }

        }

        System.out.println("-------");

    }

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

        showCommittedMemory();

        final int chunkSize = 1024 * 1024 * 100;

        List<byte[]> chunks = new ArrayList<byte[]>(100);

        try {

            for (;;) {

                byte[] chunk = new byte[chunkSize];

                touchPages(chunk);

                chunks.add(chunk);

            }

        } catch (OutOfMemoryError e) {

            chunks.set(0, null);        // Free up one chunk

            System.gc();

            int size = chunks.size();

            System.out.printf("size=%.2gGB%n", (double)size/10);

            showCommittedMemory();

            // Can we fork/exec in our current bloated state?

            Process p = new ProcessBuilder("/bin/true").start();

            p.waitFor();

        }

    }

}