并发基础
- 并发小测试
java.util.concurrent.Semaphore 类
public class SemTest {
/**
* Semaphore 通常用来控制同时有多少个线程在运行
*/
private static Semaphore semaphore = new Semaphore(1);
// private static Semaphore semaphore = new Semaphore(3);
static class car implements Runnable {
@Override
public void run() {
try {
semaphore.acquire();
System.out.println(Thread.currentThread().getName() + "start ");
System.out.println(Thread.currentThread().getName() + "end");
semaphore.release();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
ExecutorService service = Executors.newCachedThreadPool();
Thread thread = new Thread(new car(), "小汽车1");
Thread thread2 = new Thread(new car(), "小汽车2");
Thread thread3 = new Thread(new car(), "小汽车3");
List<Thread> list = new ArrayList<Thread>();
list.add(thread);
list.add(thread2);
list.add(thread3);
for (int i = 0; i < list.size(); i++) {
service.execute(list.get(i));
}
}
}
@Slf4j
public class CountExample {
private static int threadTotal = 1;
private static int clientTotal = 5000;
private static long count = 0;
public static void main(String[] args) {
ExecutorService exec = Executors.newCachedThreadPool();
final Semaphore semaphore = new Semaphore(threadTotal);
for (int index = 0; index < clientTotal; index++) {
exec.execute(() -> {
try {
semaphore.acquire();
add();
semaphore.release();
} catch (Exception e) {
log.error("exception", e);
}
});
}
exec.shutdown();
log.info("count:{}", count);
}
private static void add() {
count++;
}
}
并发: 多个线程操作相同的资源,保证线程安全,合理使用资源
高并发: 服务器同时处理很多请求,提高程序性能