1 /*
2 * Copyright 2010 Google, 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 import java.util.LinkedList;
26 import sun.misc.Continuation;
27
28 /*
29 * This class demonstrates the continuation feature by implementing a
30 * user-thread-like object.
31 */
32 public class ContinuationTest9 {
33 private static int ITER = 10000;
34
35 public static void test() throws Exception {
36 Runnable r1 = new Runnable() {
37 public void run() {
38 while (true) {
39 System.out.println("t1: " + counter++);
40 UserThread.yield();
41 if (counter > ITER) {
42 return;
43 }
44 }
45 }};
46 Runnable r2 = new Runnable() {
47 public void run() {
48 while (true) {
49 System.out.println("t2: " + counter++);
50 UserThread.yield();
51 if (counter > ITER) {
52 return;
53 }
54 }
55 }};
56 UserThread t1 = new UserThread(r1);
57 UserThread t2 = new UserThread(r2);
58 t1.start();
59 t2.start();
60 UserThread.join();
61 }
62
63 private static int counter = 0;
64
65 public static void main(String[] args) throws Exception {
66 test();
67 System.exit(0);
68 }
69 }
70
71 class UserThread {
72 // The schedule queue
73 private static final LinkedList<UserThread> queue = new LinkedList<UserThread>();
74 // The currently scheduled UserThread
75 private static UserThread currentThread;
76 // Used to synchronize between the internal thread and the outside world
77 // This guards queue, nthreads and currentThread
78 private static final Object lock = new Object();
79 // The number of live UserThreads
80 private static int nthreads = 0;
81 // Lock for join
82 private static final Object awaitLock = new Object();
83
84 // The backing Java thread that executes
85 // all UserThreads
86 private static final Thread jthread =
87 new Thread(new Runnable() {
88 public void run() {
89 while (true) {
90 try {
91 UserThread ut_to_run;
92 synchronized (lock) {
93 if (queue.size() == 0) {
94 // Wait if there's no user thread to schedule
95 lock.wait();
96 }
97 // Get the user thread to be scheduled next
98 ut_to_run = queue.remove();
99 currentThread = ut_to_run;
100 }
101 final UserThread ut = ut_to_run;
102 final Continuation c = ut.continuation;
103 // If it's scheduled for the first time,
104 if (c == null) {
105 // simply execute the given Runnable in a scope
106 Continuation.enter(ut.runnable, null);
107 } else {
108 // Otherwise, resume the saved continuation
109 Runnable r = new Runnable() {
110 public void run() {
111 c.resume(null);
112 }};
113 Continuation.enter(r, null);
114 }
115 } catch (Throwable t) {
116 throw new RuntimeException(t);
117 }
118 }
119 }
120 });
121
122 static {
123 jthread.start();
124 }
125
126 private final Runnable runnable;
127 private Continuation continuation;
128
129 public UserThread(final Runnable r) {
130 runnable = new Runnable() {
131 public void run() {
132 r.run();
133 UserThread.exit();
134 }
135 };
136 }
137
138 public void start() {
139 synchronized(lock) {
140 nthreads++;
141 // Add the given user thread to the schedule queue
142 queue.add(this);
143 // Notify the Java thread if it's waiting
144 lock.notify();
145 }
146 }
147
148 public static void yield() {
149 // Create a new continuation for each yield
150 final Continuation c = new Continuation();
151 synchronized (lock) {
152 // Save it in the user thread
153 currentThread.continuation = c;
154 // Put the user thread back to the schedule queue
155 queue.add(currentThread);
156 }
157 // Save the current scope into it. It will cause
158 // the enter at the bottom of the scope to return.
159 c.save();
160 }
161
162 private static void exit() {
163 int new_nthreads;
164 synchronized (lock) {
165 nthreads--;
166 new_nthreads = nthreads;
167 if (new_nthreads == 0) {
168 synchronized (awaitLock) {
169 awaitLock.notify();
170 }
171 }
172 }
173 }
174
175 public static void join() throws InterruptedException {
176 synchronized (awaitLock) {
177 awaitLock.wait();
178 }
179 }
180 }