Java和Round-Robin上的AtomicInteger

AtomicInteger属于Atomic Variables族。主要好处是使用它不会阻塞而不是进行阻塞同步，因此避免了线程的挂起和重新调度。

AtomicInteger基于“比较和交换”机制，并且是原子变量的标量组的一部分。

我们的第一个用例是可以多次访问的网页上的功能。

 package com.gkatzioura.concurrency;  import java.util.concurrent.atomic.AtomicInteger;  public class AtomicIntegerExample { private AtomicInteger atomicInteger = new AtomicInteger(); public void serveRequest() { atomicInteger.incrementAndGet(); /** * logic */ } public int requestsServed() { return atomicInteger.get(); }  }

并测试我们的用例

 package com.gkatzioura.concurrency;  import java.util.ArrayList;  import java.util.List;  import java.util.concurrent.ExecutionException;  import java.util.concurrent.ExecutorService;  import java.util.concurrent.Executors;  import java.util.concurrent.Future;  import org.junit.jupiter.api.Assertions;  import org.junit.jupiter.api.BeforeEach;  import org.junit.jupiter.api.Test;  public class AtomicIntegerExampleTest { private AtomicIntegerExample atomicIntegerExample; @BeforeEach void setUp() { atomicIntegerExample = new AtomicIntegerExample(); } @Test void testConcurrentIncrementAndGet() throws ExecutionException, InterruptedException { final int threads = 10 ; ExecutorService executorService = Executors.newFixedThreadPool(threads); List<Future> futures = new ArrayList(); for ( int i = 0 ; i { atomicIntegerExample.serveRequest(); return null ; })); } for (Future future: futures) { future.get(); } Assertions.assertEquals( 10 ,atomicIntegerExample.requestsServed()); }  }

除了使用原子整数作为计数器之外，您还可以在各种情况下使用它。例如线程安全的循环算法。

 package com.gkatzioura.concurrency;  import java.util.concurrent.atomic.AtomicInteger;  public class AtomicIntegerRoundRobin { private final int totalIndexes; private final AtomicInteger atomicInteger = new AtomicInteger(- 1 ); public AtomicIntegerRoundRobin( int totalIndexes) { this .totalIndexes = totalIndexes; } public int index() { int currentIndex; int nextIndex; do { currentIndex = atomicInteger.get(); nextIndex = currentIndex< Integer.MAX_VALUE ? currentIndex+ nextIndex = currentIndex< Integer.MAX_VALUE ? currentIndex+ 1 : 0 ; } while (!atomicInteger.compareAndSet(currentIndex, nextIndex)); return nextIndex % totalIndexes; }  }

totalIndex是索引的总数。当请求下一个索引的请求时，计数器将增加，并进行比较和设置操作。如果由于另一个线程而失败，则它将再次尝试该操作，并将获得计数器的下一个值。
模运算将给出当前索引。如果原子整数达到最大值，则应将其重置为零。重置会导致边缘情况并更改索引的顺序。如果这是一个问题，则可以根据总索引大小来调整最大值以避免这种情况。

还对此进行了一些测试。

 package com.gkatzioura.concurrency;  import java.util.ArrayList;  import java.util.List;  import java.util.concurrent.ExecutionException;  import java.util.concurrent.ExecutorService;  import java.util.concurrent.Executors;  import java.util.concurrent.Future;  import org.junit.jupiter.api.Assertions;  import org.junit.jupiter.api.BeforeEach;  import org.junit.jupiter.api.Test;  AtomicIntegerRoundRobinTest { class AtomicIntegerRoundRobinTest { private static final int MAX_INDEX = 10 ; private AtomicIntegerRoundRobin atomicIntegerRoundRobin; @BeforeEach void setUp() { atomicIntegerRoundRobin = new AtomicIntegerRoundRobin(MAX_INDEX); } @Test void testIndexesSerially() { for ( long i= 0 ;i<MAX_INDEX* 20 ;i++) { System.out.println(atomicIntegerRoundRobin.index()); } Assertions.assertEquals( 0 , atomicIntegerRoundRobin.index()); } @Test void testIndexesConcurrently() throws ExecutionException, InterruptedException { ExecutorService executorService = Executors.newFixedThreadPool( 4 ); List<Future> futures = new ArrayList(); for ( int i = 0 ; i atomicIntegerRoundRobin.index())); } for (Future future: futures) { System.out.println(future.get()); } Assertions.assertEquals( 0 ,atomicIntegerRoundRobin.index()); }  }