1 /* 2 * Copyright (c) 2003, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * 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 }