J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2003 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. |
| 8 | * |
| 9 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 12 | * version 2 for more details (a copy is included in the LICENSE file that |
| 13 | * accompanied this code). |
| 14 | * |
| 15 | * You should have received a copy of the GNU General Public License version |
| 16 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 17 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 18 | * |
| 19 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 20 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 21 | * have any questions. |
| 22 | */ |
| 23 | |
| 24 | /* @test |
| 25 | @bug 4843136 4763384 |
| 26 | @summary Various race conditions caused exec'ed processes to have |
| 27 | extra unused file descriptors, which caused hard-to-reproduce hangs. |
| 28 | @author Martin Buchholz |
| 29 | */ |
| 30 | |
| 31 | import java.util.Timer; |
| 32 | import java.util.TimerTask; |
| 33 | import java.io.IOException; |
| 34 | |
| 35 | public class SleepyCat { |
| 36 | |
| 37 | private static void destroy (Process[] deathRow) { |
| 38 | for (int i = 0; i < deathRow.length; ++i) |
| 39 | if (deathRow[i] != null) |
| 40 | deathRow[i].destroy(); |
| 41 | } |
| 42 | |
| 43 | static class TimeoutTask extends TimerTask { |
| 44 | private Process[] deathRow; |
| 45 | private boolean timedOut; |
| 46 | |
| 47 | TimeoutTask (Process[] deathRow) { |
| 48 | this.deathRow = deathRow; |
| 49 | this.timedOut = false; |
| 50 | } |
| 51 | |
| 52 | public void run() { |
| 53 | timedOut = true; |
| 54 | destroy(deathRow); |
| 55 | } |
| 56 | |
| 57 | public boolean timedOut() { |
| 58 | return timedOut; |
| 59 | } |
| 60 | } |
| 61 | |
| 62 | private static boolean hang1() throws IOException, InterruptedException { |
| 63 | // Time out was reproducible on Solaris 50% of the time; |
| 64 | // on Linux 80% of the time. |
| 65 | // |
| 66 | // Scenario: After fork(), parent executes and closes write end of child's stdin. |
| 67 | // This causes child to retain a write end of the same pipe. |
| 68 | // Thus the child will never see an EOF on its stdin, and will hang. |
| 69 | Runtime rt = Runtime.getRuntime(); |
| 70 | // Increasing the iteration count makes the bug more |
| 71 | // reproducible not only for the obvious reason, but also for |
| 72 | // the subtle reason that it makes reading /proc/getppid()/fd |
| 73 | // slower, making the child more likely to win the race! |
| 74 | int iterations = 20; |
| 75 | int timeout = 30; |
| 76 | String[] catArgs = new String[] {"/bin/cat"}; |
| 77 | String[] sleepArgs = new String[] {"/bin/sleep", |
| 78 | String.valueOf(timeout+1)}; |
| 79 | Process[] cats = new Process[iterations]; |
| 80 | Process[] sleeps = new Process[iterations]; |
| 81 | Timer timer = new Timer(true); |
| 82 | TimeoutTask catExecutioner = new TimeoutTask(cats); |
| 83 | timer.schedule(catExecutioner, timeout * 1000); |
| 84 | |
| 85 | for (int i = 0; i < cats.length; ++i) { |
| 86 | cats[i] = rt.exec(catArgs); |
| 87 | java.io.OutputStream s = cats[i].getOutputStream(); |
| 88 | Process sleep = rt.exec(sleepArgs); |
| 89 | s.close(); // race condition here |
| 90 | sleeps[i] = sleep; |
| 91 | } |
| 92 | |
| 93 | for (int i = 0; i < cats.length; ++i) |
| 94 | cats[i].waitFor(); // hangs? |
| 95 | |
| 96 | timer.cancel(); |
| 97 | |
| 98 | destroy(sleeps); |
| 99 | |
| 100 | if (catExecutioner.timedOut()) |
| 101 | System.out.println("Child process has a hidden writable pipe fd for its stdin."); |
| 102 | return catExecutioner.timedOut(); |
| 103 | } |
| 104 | |
| 105 | private static boolean hang2() throws Exception { |
| 106 | // Inspired by the imaginative test case for |
| 107 | // 4850368 (process) getInputStream() attaches to forked background processes (Linux) |
| 108 | |
| 109 | // Time out was reproducible on Linux 80% of the time; |
| 110 | // never on Solaris because of explicit close in Solaris-specific code. |
| 111 | |
| 112 | // Scenario: After fork(), the parent naturally closes the |
| 113 | // child's stdout write end. The child dup2's the write end |
| 114 | // of its stdout onto fd 1. On Linux, it fails to explicitly |
| 115 | // close the original fd, and because of the parent's close() |
| 116 | // of the fd, the child retains it. The child thus ends up |
| 117 | // with two copies of its stdout. Thus closing one of those |
| 118 | // write fds does not have the desired effect of causing an |
| 119 | // EOF on the parent's read end of that pipe. |
| 120 | Runtime rt = Runtime.getRuntime(); |
| 121 | int iterations = 10; |
| 122 | Timer timer = new Timer(true); |
| 123 | int timeout = 30; |
| 124 | Process[] backgroundSleepers = new Process[iterations]; |
| 125 | TimeoutTask sleeperExecutioner = new TimeoutTask(backgroundSleepers); |
| 126 | timer.schedule(sleeperExecutioner, timeout * 1000); |
| 127 | byte[] buffer = new byte[10]; |
| 128 | String[] args = |
| 129 | new String[] {"/bin/sh", "-c", |
| 130 | "exec sleep " + (timeout+1) + " >/dev/null"}; |
| 131 | |
| 132 | for (int i = 0; |
| 133 | i < backgroundSleepers.length && !sleeperExecutioner.timedOut(); |
| 134 | ++i) { |
| 135 | backgroundSleepers[i] = rt.exec(args); // race condition here |
| 136 | try { |
| 137 | // should get immediate EOF, but might hang |
| 138 | if (backgroundSleepers[i].getInputStream().read() != -1) |
| 139 | throw new Exception("Expected EOF, got a byte"); |
| 140 | } catch (IOException e) { |
| 141 | // Stream closed by sleeperExecutioner |
| 142 | break; |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | timer.cancel(); |
| 147 | |
| 148 | destroy(backgroundSleepers); |
| 149 | |
| 150 | if (sleeperExecutioner.timedOut()) |
| 151 | System.out.println("Child process has two (should be one) writable pipe fds for its stdout."); |
| 152 | return sleeperExecutioner.timedOut(); |
| 153 | } |
| 154 | |
| 155 | public static void main (String[] args) throws Exception { |
| 156 | try { |
| 157 | if (hang1() | hang2()) |
| 158 | throw new Exception("Read from closed pipe hangs"); |
| 159 | } catch (IOException e) { |
| 160 | // We will get here on non-Posix systems, |
| 161 | // which don't have cat and sleep and sh. |
| 162 | } |
| 163 | } |
| 164 | } |