test/loops/ContextSwitchTest.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;

public final class ContextSwitchTest {
    static final int iters = 1000000;
    static AtomicReference turn = new AtomicReference();
    public static void main(String[] args) throws Exception {
        test();
        test();
        test();
    }

    static void test() throws Exception {
        MyThread a = new MyThread();
        MyThread b = new MyThread();
        a.other = b;
        b.other = a;
        turn.set(a);
        long startTime = System.nanoTime();
        a.start();
        b.start();
        a.join();
        b.join();
        long endTime = System.nanoTime();
        int np = a.nparks + b.nparks;
        System.out.println("Average time: " +
                           ((endTime - startTime) / np) +
                           "ns");
    }

    static final class MyThread extends Thread {

        static {
            // Reduce the risk of rare disastrous classloading in first call to
            // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
            Class<?> ensureLoaded = LockSupport.class;
        }

        volatile Thread other;
        volatile int nparks;

        public void run() {
            final AtomicReference t = turn;
            final Thread other = this.other;
            if (turn == null || other == null)
                throw new NullPointerException();
            int p = 0;
            for (int i = 0; i < iters; ++i) {
                while (!t.compareAndSet(other, this)) {
                    LockSupport.park();
                    ++p;
                }
                LockSupport.unpark(other);
            }
            LockSupport.unpark(other);
            nparks = p;
            System.out.println("parks: " + p);
        }
    }
}
Revision:	1.9
Committed:	Mon Oct 12 20:16:47 2015 UTC (8 years, 7 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.8:	+7 -0 lines
Log Message:	guard against lost unpark via JDK-8074773
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4	jsr166	1.6	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	jsr166	1.7	import java.util.*;
8	dl	1.1	import java.util.concurrent.*;
9	jsr166	1.7	import java.util.concurrent.atomic.*;
10	dl	1.1	import java.util.concurrent.locks.*;
11
12			public final class ContextSwitchTest {
13	jsr166	1.5	static final int iters = 1000000;
14	dl	1.1	static AtomicReference turn = new AtomicReference();
15			public static void main(String[] args) throws Exception {
16	dl	1.3	test();
17			test();
18			test();
19			}
20
21			static void test() throws Exception {
22	dl	1.1	MyThread a = new MyThread();
23			MyThread b = new MyThread();
24			a.other = b;
25			b.other = a;
26			turn.set(a);
27			long startTime = System.nanoTime();
28			a.start();
29			b.start();
30			a.join();
31			b.join();
32			long endTime = System.nanoTime();
33			int np = a.nparks + b.nparks;
34	jsr166	1.4	System.out.println("Average time: " +
35	dl	1.3	((endTime - startTime) / np) +
36			"ns");
37	dl	1.1	}
38
39			static final class MyThread extends Thread {
40	jsr166	1.9
41			static {
42			// Reduce the risk of rare disastrous classloading in first call to
43			// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
44			Class<?> ensureLoaded = LockSupport.class;
45			}
46
47	dl	1.1	volatile Thread other;
48			volatile int nparks;
49
50			public void run() {
51	dl	1.3	final AtomicReference t = turn;
52			final Thread other = this.other;
53	jsr166	1.4	if (turn == null \|\| other == null)
54	dl	1.3	throw new NullPointerException();
55	dl	1.1	int p = 0;
56			for (int i = 0; i < iters; ++i) {
57	dl	1.3	while (!t.compareAndSet(other, this)) {
58	dl	1.1	LockSupport.park();
59			++p;
60			}
61			LockSupport.unpark(other);
62			}
63			LockSupport.unpark(other);
64			nparks = p;
65			System.out.println("parks: " + p);
66			}
67			}
68			}