1 /*
   2  * Copyright (c) 2005, 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 4905777
  26    @summary PrintStream.println(Object) oversynchronized, can deadlock
  27    @key randomness
  28 */
  29 
  30 import java.io.PrintStream;
  31 
  32 public class OversynchronizedTest extends Thread {
  33     private static TestObj testObj = new TestObj("This is a test.");
  34     private static int loopNum = 100;
  35 
  36     public void run() {
  37         for(int i=0; i<loopNum; i++) {
  38             testObj.test();
  39 
  40             //passing an object to System.out.println might cause deadlock
  41             //if the object has a synchronized toString() method.
  42             //using System.out.println(testObj.toString()) won't have a problem
  43            System.out.println(testObj);
  44         }
  45     }
  46 
  47     public static void main(String args[]) throws Exception {
  48         // should no NullPointerException
  49         System.out.println((Object)null);
  50 
  51         // over synch test
  52         int num = 5;
  53 
  54         OversynchronizedTest[] t = new OversynchronizedTest[num];
  55         for(int i=0; i<num; i++) {
  56             t[i] = new OversynchronizedTest();
  57             t[i].start();
  58         }
  59 
  60         for(int i=0; i <num; i++) {
  61             t[i].join();
  62         }
  63 
  64         System.out.println("Test completed.");
  65     }
  66 }
  67 
  68 class TestObj {
  69     String mStr;
  70 
  71     TestObj(String str) {
  72         mStr = str;
  73     }
  74 
  75     synchronized void test() {
  76         try {
  77             long t = Math.round(Math.random()*10);
  78             Thread.currentThread().sleep(t);
  79         } catch (InterruptedException e) {
  80             // jtreg timeout?
  81             // Only jtreg will interrupt this thread so it knows what to do:
  82             e.printStackTrace();
  83         }
  84 
  85         //the following line might cause hang if there is System.out.println(testObj)
  86         //called by other threads.
  87         System.out.println("In test().");
  88     }
  89 
  90     synchronized public String toString() {
  91         System.out.println("Calling toString\n");
  92         return mStr;
  93     }
  94 }