错误的例子:
@ThreadSafe
@Slf4j
public class AtomicExample6 {
// 总的请求个数
public static final int requestTotal = 1000;
// 同一时刻最大的并发线程的个数
public static final int concurrentThreadNum = 20;
private static Boolean isHappened_ = false;
public static void main(String[] args) throws InterruptedException {
ExecutorService executorService = Executors.newFixedThreadPool(concurrentThreadNum);
CountDownLatch countDownLatch = new CountDownLatch(requestTotal);
Semaphore semaphore = new Semaphore(concurrentThreadNum);
for (int i = 0; i< requestTotal; i++) {
executorService.execute(()->{
try {
semaphore.acquire();
test();
semaphore.release();
} catch (InterruptedException e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("请求完成");
}
private static void test() {
if (isHappened_ == false) {
isHappened_ = true;
log.info("hapen 1");
}
}
}
分析:
上面的代码先实现只执行一次方法test(),实际上在并发实现的时候可能执行多次。
输出结果:
[pool-1-thread-3] INFO com.example.concurrent.example.count.AtomicExample6 - hapen 1
[pool-1-thread-2] INFO com.example.concurrent.example.count.AtomicExample6 - hapen 1
[main] INFO com.example.concurrent.example.count.AtomicExample6 - 请求完成
正确的程序代码(通过AtomicBoolean):
@ThreadSafe
@Slf4j
public class AtomicExample6 {
// 总的请求个数
public static final int requestTotal = 1000;
// 同一时刻最大的并发线程的个数
public static final int concurrentThreadNum = 20;
private static AtomicBoolean isHappened = new AtomicBoolean(false);
public static void main(String[] args) throws InterruptedException {
ExecutorService executorService = Executors.newFixedThreadPool(concurrentThreadNum);
CountDownLatch countDownLatch = new CountDownLatch(requestTotal);
Semaphore semaphore = new Semaphore(concurrentThreadNum);
for (int i = 0; i< requestTotal; i++) {
executorService.execute(()->{
try {
semaphore.acquire();
test();
semaphore.release();
} catch (InterruptedException e) {
log.error("exception", e);
}
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
log.info("请求完成");
}
private static void test() {
if (isHappened.compareAndSet(false, true)) { // 这段代码可以保证执行执行一次
log.info("happen 1");
}
}
}