58 lines
1.6 KiB
Java
58 lines
1.6 KiB
Java
// lowlevel/AttemptLocking.java
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// (c)2020 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Locks in the concurrent library allow you
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// to give up on trying to acquire a lock
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import java.util.concurrent.*;
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import java.util.concurrent.locks.*;
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import onjava.Nap;
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public class AttemptLocking {
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private ReentrantLock lock = new ReentrantLock();
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public void untimed() {
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boolean captured = lock.tryLock();
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try {
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System.out.println("tryLock(): " + captured);
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} finally {
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if(captured)
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lock.unlock();
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}
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}
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public void timed() {
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boolean captured = false;
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try {
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captured = lock.tryLock(2, TimeUnit.SECONDS);
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} catch(InterruptedException e) {
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throw new RuntimeException(e);
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}
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try {
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System.out.println(
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"tryLock(2, TimeUnit.SECONDS): " + captured);
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} finally {
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if(captured)
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lock.unlock();
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}
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}
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public static void main(String[] args) {
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final AttemptLocking al = new AttemptLocking();
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al.untimed(); // True -- lock is available
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al.timed(); // True -- lock is available
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// Now create a second task to grab the lock:
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CompletableFuture.runAsync( () -> {
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al.lock.lock();
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System.out.println("acquired");
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});
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new Nap(0.1); // Give the second task a chance
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al.untimed(); // False -- lock grabbed by task
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al.timed(); // False -- lock grabbed by task
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}
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}
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/* Output:
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tryLock(): true
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tryLock(2, TimeUnit.SECONDS): true
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acquired
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tryLock(): false
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tryLock(2, TimeUnit.SECONDS): false
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*/
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