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  1. JDK
  2. JDK-8027348

(process) Enhancement of handling async close of ProcessInputStream

    Details

    • Type: Enhancement
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: 7u60, 8
    • Fix Version/s: 9
    • Component/s: core-libs
    • Subcomponent:
    • Resolved In Build:
      b03

      Backports

        Description

        Here's proposal by Martin Buchholz:

        After rebasing, I propose this change which is shorter and is more obviously correct.

        diff --git a/src/solaris/classes/java/lang/UNIXProcess.java.linux b/src/solaris/classes/java/lang/UNIXProcess.java.linux
        --- a/src/solaris/classes/java/lang/UNIXProcess.java.linux
        +++ b/src/solaris/classes/java/lang/UNIXProcess.java.linux
        @@ -344,47 +344,39 @@
                 ProcessPipeInputStream(int fd) {
                     super(new FileInputStream(newFileDescriptor(fd)));
                 }
        -
        - private InputStream drainInputStream(InputStream in)
        + private static byte[] drainInputStream(InputStream in)
                         throws IOException {
                     int n = 0;
                     int j;
                     byte[] a = null;
        - synchronized (closeLock) {
        - if (buf == null) // asynchronous close()?
        - return null; // discard
        - j = in.available();
        + while ((j = in.available()) > 0) {
        + a = (a == null) ? new byte[j] : Arrays.copyOf(a, n + j);
        + n += in.read(a, n, j);
                     }
        - while (j > 0) {
        - a = (a == null) ? new byte[j] : Arrays.copyOf(a, n + j);
        - synchronized (closeLock) {
        - if (buf == null) // asynchronous close()?
        - return null; // discard
        - n += in.read(a, n, j);
        - j = in.available();
        - }
        - }
        - return (a == null) ?
        - ProcessBuilder.NullInputStream.INSTANCE :
        - new ByteArrayInputStream(n == a.length ? a : Arrays.copyOf(a, n));
        + return (a == null || n == a.length) ? a : Arrays.copyOf(a, n);
                 }
         
                 /** Called by the process reaper thread when the process exits. */
                 synchronized void processExited() {
        - try {
        - InputStream in = this.in;
        - if (in != null) {
        - InputStream stragglers = drainInputStream(in);
        - in.close();
        - this.in = stragglers;
        - }
        - } catch (IOException ignored) { }
        + synchronized (closeLock) {
        + try {
        + InputStream in = this.in;
        + // this stream is closed if and only if: in == null
        + if (in != null) {
        + byte[] stragglers = drainInputStream(in);
        + in.close();
        + this.in = (stragglers == null) ?
        + ProcessBuilder.NullInputStream.INSTANCE :
        + new ByteArrayInputStream(stragglers);
        + }
        + } catch (IOException ignored) {}
        + }
                 }
         
                 @Override
                 public void close() throws IOException {
                     // BufferedInputStream#close() is not synchronized unlike most other methods.
        - // Synchronizing helps avoid racing with drainInputStream().
        + // Synchronizing helps avoid race with processExited().
                     synchronized (closeLock) {
                         super.close();
                     }




        I propose the test for this be in test/java/lang/ProcessBuilder/ instead of test/java/lang/Runtime/exec and that

        - it runs for only 2 seconds by default. This is the shortest time that a failure was detected. 20 seconds is way too long.
        - it is much more likely to fail quickly than the original version.

        Only tested on Linux. There is porting work to be done (testing other platforms).
        I would like y'all (Ivan?) to adopt this.

        /*
         * Copyright (c) 2013, Oracle and/or its affiliates. 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.
         *
         * 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
         * @bug 8024521
         * @summary Closing ProcessPipeInputStream at the time the process exits is racy
         * and leads to data corruption. Run this test manually (as
         * an ordinary java program) with -Xmx8M to repro bug 8024521.
         * @run main/othervm -Xmx8M -Dtest.duration=2 CloseRace
         */

        import java.io.*;
        import java.util.ArrayList;
        import java.util.List;

        public class CloseRace {
            private static final String BIG_FILE = "bigfile";

            private static final int[] procFDs = new int[6];

            /** default value sufficient to repro bug 8024521. */
            private static final int testDurationSeconds
                = Integer.getInteger("test.duration", 600);
            
            static boolean fdInUse(int i) {
                return new File("/proc/self/fd/" + i).exists();
            }

            static boolean[] procFDsInUse() {
                boolean[] inUse = new boolean[procFDs.length];
                for (int i = 0; i < procFDs.length; i++)
                    inUse[i] = fdInUse(procFDs[i]);
                return inUse;
            }

            static int count(boolean[] bits) {
                int count = 0;
                for (int i = 0; i < bits.length; i++)
                    count += bits[i] ? 1 : 0;
                return count;
            }

            public static void main(String args[]) throws Exception {
                if (!(new File("/proc/self/fd").isDirectory()))
                    return;

                // Catch Errors from process reaper
                Thread.setDefaultUncaughtExceptionHandler
                    ((t, e) -> { e.printStackTrace(); System.exit(1); });

                try (RandomAccessFile f = new RandomAccessFile(BIG_FILE, "rw")) {
                    f.setLength(Runtime.getRuntime().maxMemory()); // provoke OOME
                }

                for (int i = 0, j = 0; j < procFDs.length; i++)
                    if (!fdInUse(i))
                        procFDs[j++] = i;

                Thread[] threads = {
                    new Thread(new OpenLoop()),
                    new Thread(new ExecLoop()),
                };
                for (Thread thread : threads)
                    thread.start();

                Thread.sleep(testDurationSeconds * 1000);

                for (Thread thread : threads)
                    thread.interrupt();
                for (Thread thread : threads)
                    thread.join();
            }

            static class OpenLoop implements Runnable {
                public void run() {
                    while (!Thread.interrupted()) {
                        try {
                            // wait for ExecLoop to finish creating process
                            do {} while (count(procFDsInUse()) != 3);
                            List<InputStream> iss = new ArrayList<>(4);

                            // eat up three "holes" (closed ends of pipe fd pairs)
                            for (int i = 0; i < 3; i++)
                                iss.add(new FileInputStream(BIG_FILE));
                            do {} while (count(procFDsInUse()) == procFDs.length);
                            // hopefully this will racily occupy empty fd slot
                            iss.add(new FileInputStream(BIG_FILE));
                            Thread.sleep(1); // Widen race window
                            for (InputStream is : iss)
                                is.close();
                        } catch (InterruptedException e) {
                            break;
                        } catch (Exception e) {
                            throw new Error(e);
                        }
                    }
                }
            }

            static class ExecLoop implements Runnable {
                public void run() {
                    ProcessBuilder builder = new ProcessBuilder("/bin/true");
                    while (!Thread.interrupted()) {
                        try {
                            // wait for OpenLoop to finish
                            do {} while (count(procFDsInUse()) > 0);
                            Process process = builder.start();
                            InputStream is = process.getInputStream();
                            process.waitFor();
                            is.close();
                        } catch (InterruptedException e) {
                            break;
                        } catch (Exception e) {
                            throw new Error(e);
                        }
                    }
                }
            }
        }


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                • Assignee:
                  igerasim Ivan Gerasimov
                  Reporter:
                  igerasim Ivan Gerasimov
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                  • Created:
                    Updated:
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