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