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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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import java.util.*; |
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import java.util.concurrent.*; |
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import java.util.concurrent.atomic.*; |
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import java.util.concurrent.locks.*; |
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|
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public final class ContextSwitchTest { |
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static final int iters = 1000000; |
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static AtomicReference turn = new AtomicReference(); |
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public static void main(String[] args) throws Exception { |
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test(); |
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test(); |
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test(); |
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} |
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|
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static void test() throws Exception { |
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MyThread a = new MyThread(); |
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MyThread b = new MyThread(); |
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a.other = b; |
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b.other = a; |
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turn.set(a); |
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long startTime = System.nanoTime(); |
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a.start(); |
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b.start(); |
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a.join(); |
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b.join(); |
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long endTime = System.nanoTime(); |
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int np = a.nparks + b.nparks; |
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System.out.println("Average time: " + |
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((endTime - startTime) / np) + |
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"ns"); |
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} |
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|
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static final class MyThread extends Thread { |
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|
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static { |
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// Reduce the risk of rare disastrous classloading in first call to |
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// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
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Class<?> ensureLoaded = LockSupport.class; |
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} |
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|
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volatile Thread other; |
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volatile int nparks; |
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|
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public void run() { |
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final AtomicReference t = turn; |
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final Thread other = this.other; |
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if (turn == null || other == null) |
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throw new NullPointerException(); |
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int p = 0; |
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for (int i = 0; i < iters; ++i) { |
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while (!t.compareAndSet(other, this)) { |
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LockSupport.park(); |
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++p; |
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} |
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LockSupport.unpark(other); |
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} |
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LockSupport.unpark(other); |
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nparks = p; |
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System.out.println("parks: " + p); |
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} |
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} |
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} |
