1 /*

     2  * Copyright (c) 2004, 2014, 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 

    25 /*

    26  *

    27  *   Sample target application for jvmti demos

    28  *

    29  *     java Context [threadCount [iterationCount [sleepContention]]]

    30  *           Default: java Context 5 10 0

    31  *

    32  *      threadCount     Number of threads

    33  *      iterationCount  Total turns taken for all threads

    34  *      sleepContention Time for main thread to sleep while holding lock

    35  *                      (creates monitor contention on all other threads)

    36  *

    37  */

    38 

    39 /* Used to sync up turns and keep track of who's turn it is */

    40 final class TurnChecker {

    41     int thread_index;

    42     TurnChecker(int thread_index) {

    43         this.thread_index = thread_index;

    44     }

    45 }

    46 

    47 /* Creates a bunch of threads that sequentially take turns */

    48 public final class Context extends Thread {

    49     /* Used to track threads */

    50     private static long startTime;

    51     private static TurnChecker turn = new TurnChecker(-1);

    52     private static int total_turns_taken;

    53 

    54     /* Used for each Context thread */

    55     private final int thread_count;

    56     private final int thread_index;

    57     private final int thread_turns;

    58 

    59     /* Main program */

    60     public static void main(String[] argv) throws InterruptedException {

    61         int default_thread_count = 5;

    62         int default_thread_turns = 10;

    63         int default_contention_sleep = 0;

    64         int expected_turns_taken;

    65         long sleepTime = 10L;

    66 

    67         /* Override defaults */

    68         if ( argv.length >= 1 ) {

    69             default_thread_count = Integer.parseInt(argv[0]);

    70         }

    71         if ( argv.length >= 2 ) {

    72             expected_turns_taken = Integer.parseInt(argv[1]);

    73             default_thread_turns = expected_turns_taken/default_thread_count;

    74         }

    75         expected_turns_taken = default_thread_count*default_thread_turns;

    76         if ( argv.length >= 3 ) {

    77             default_contention_sleep = Integer.parseInt(argv[2]);

    78         }

    79 

    80         System.out.println("Context started with "

    81                  + default_thread_count + " threads and "

    82                  + default_thread_turns + " turns per thread");

    83 

    84         /* Get all threads running (they will block until we set turn) */

    85         for (int i = 0; i < default_thread_count; i++) {

    86             new Context(default_thread_count, i, default_thread_turns).start();

    87         }

    88 

    89         /* Sleep to make sure thread_index 0 make it to the wait call */

    90         System.out.println("Context sleeping, so threads will start wait");

    91         Thread.yield();

    92         Thread.sleep(sleepTime);

    93 

    94         /* Save start time */

    95         startTime = System.currentTimeMillis();

    96 

    97         /* This triggers the starting of taking turns */

    98         synchronized (turn) {

    99             turn.thread_index = 0;

   100             turn.notifyAll();

   101         }

   102         System.out.println("Context sleeping, so threads can run");

   103         Thread.yield();

   104         Thread.sleep(sleepTime);

   105 

   106         /* Wait for threads to finish (after everyone has had their turns) */

   107         while ( true ) {

   108             boolean done;

   109             done = false;

   110             synchronized (turn) {

   111                 if ( total_turns_taken == expected_turns_taken ) {

   112                     done = true;

   113                 }

   114                 /* Create some monitor contention by sleeping with lock */

   115                 if ( default_contention_sleep > 0 ) {

   116                     System.out.println("Context sleeping, to create contention");

   117                     Thread.yield();

   118                     Thread.sleep((long)default_contention_sleep);

   119                 }

   120             }

   121             if ( done )

   122                 break;

   123             System.out.println("Context sleeping, so threads will complete");

   124             Thread.sleep(sleepTime);

   125         }

   126 

   127         long endTime   = System.currentTimeMillis();

   128         long totalTime = endTime - startTime;

   129 

   130         System.out.println("Total time (milliseconds): " + totalTime);

   131         System.out.println("Milliseconds per thread: " +

   132                            ((double)totalTime / (default_thread_count)));

   133 

   134         System.out.println("Context completed");

   135         System.exit(0);

   136     }

   137 

   138     /* Thread object to run */

   139     Context(int thread_count, int thread_index, int thread_turns) {

   140         this.thread_count = thread_count;

   141         this.thread_index = thread_index;

   142         this.thread_turns = thread_turns;

   143     }

   144 

   145     /* Main for thread */

   146     public void run() {

   147         int next_thread_index = (thread_index + 1) % thread_count;

   148         int turns_taken       = 0;

   149 

   150         try {

   151 

   152             /* Loop until we make sure we get all our turns */

   153             for (int i = 0; i < thread_turns * thread_count; i++) {

   154                 synchronized (turn) {

   155                     /* Keep waiting for our turn */

   156                     while (turn.thread_index != thread_index)

   157                         turn.wait();

   158                     /* MY TURN! Each thread gets thread_turns */

   159                     total_turns_taken++;

   160                     turns_taken++;

   161                     System.out.println("Turn #" + total_turns_taken

   162                                 + " taken by thread " + thread_index

   163                                 + ", " + turns_taken

   164                                 + " turns taken by this thread");

   165                     /* Give next thread a turn */

   166                     turn.thread_index = next_thread_index;

   167                     turn.notifyAll();

   168                 }

   169                 /* If we've had all our turns, break out of this loop */

   170                 if (thread_turns == turns_taken) {

   171                     System.out.println("Loop end: thread got " + turns_taken

   172                             + " turns, expected " + thread_turns);

   173                     break;

   174                 }

   175             }

   176         } catch (InterruptedException intEx) {

   177             System.out.println("Got an InterruptedException:" + intEx);

   178             /* skip */

   179         }

   180 

   181         /* Make sure we got all our turns */

   182         if ( thread_turns != turns_taken ) {

   183             System.out.println("ERROR: thread got " + turns_taken

   184                                         + " turns, expected " + thread_turns);

   185             System.exit(1);

   186         }

   187     }

   188 }