3Hystrix 信号量隔离 · SpringCloud微服务实战 · 看云

3.Hystrix 信号量

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Hystrix提供了两种隔离机制，信号量（SEMAPHORE）和线程（THREAD）隔离,我们先看信号量的隔离
当请求的并发数高于设定的阀值时，就不会再执行命令。相对于线程池机制，信号量的开销较小，但是信号量机制不支持超时和异步，除非对调用的服务有足够的信任，否则不建议使用信号量机制进行隔离。

注意：如果依赖关系被信号量隔离，然后变为潜在状态，则父线程将保持阻塞状态，直到基础网络调用超时为止。
一旦达到限制，信号灯拒绝将开始，但是填充信号量的线程无法得到释放

本节代码地址

GitHub: https://github.com/xuyisu/fw-sping-cloud/tree/master/fw-cloud-hystrix/fw-cloud-hystrix-without-springcloud

接下来我们在代码中看看信号量机制怎么进行隔离的

3.1 新建FwHystrixCommondSemaphore类

需要在构造方法中指定SEMAPHORE机制，这里我们用默认的最大并发数（10）和回退并发数（10），开20线程进行测试。


@Slf4j
public class FwHystrixCommondSemaphore extends HystrixCommand<String> {
    private final String name;

    protected FwHystrixCommondSemaphore(String name) {
        super(HystrixCommand.Setter
                .withGroupKey(HystrixCommandGroupKey.Factory.asKey("myGroup"))
                .andCommandPropertiesDefaults(
                HystrixCommandProperties.Setter().withExecutionIsolationStrategy(
                        HystrixCommandProperties.ExecutionIsolationStrategy.SEMAPHORE
                )
        ));
        this.name = name;
    }

    @Override
    protected String getFallback() {
        log.info(this.name+":"+Thread.currentThread().getName()+"异常");
        return this.name+":"+Thread.currentThread().getName();
    }

    @Override
    protected String run() throws Exception {
        log.info(this.name+":"+Thread.currentThread().getName()+"成功");
        return this.name + ":" + Thread.currentThread().getName();
    }


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        for (int i = 0; i <20 ; i++) {
            final int index=i;
            Thread t =new Thread() {
                @Override
                public void run() {
                    FwHystrixCommondSemaphore test = new FwHystrixCommondSemaphore("test" + index);
                    test.execute();
                }
             };
            t.start();
        }
        Thread.sleep(5000);

    }
}

3.2 运行main方法

可以看到console输出的日志

13:33:06.043 [Thread-15] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test15:Thread-15异常
13:33:06.043 [Thread-7] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test7:Thread-7异常
13:33:06.043 [Thread-11] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test11:Thread-11异常
13:33:06.043 [Thread-9] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test9:Thread-9异常
13:33:06.043 [Thread-18] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test18:Thread-18异常
13:33:06.043 [Thread-19] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test19:Thread-19异常
13:33:06.043 [Thread-12] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test12:Thread-12异常
13:33:06.043 [Thread-2] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test2:Thread-2异常
13:33:06.043 [Thread-17] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test17:Thread-17异常
13:33:06.043 [Thread-0] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test0:Thread-0异常
13:33:06.066 [Thread-6] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test6:Thread-6成功
13:33:06.066 [Thread-8] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test8:Thread-8成功
13:33:06.066 [Thread-16] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test16:Thread-16成功
13:33:06.066 [Thread-5] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test5:Thread-5成功
13:33:06.066 [Thread-3] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test3:Thread-3成功
13:33:06.066 [Thread-13] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test13:Thread-13成功
13:33:06.066 [Thread-10] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test10:Thread-10成功
13:33:06.066 [Thread-4] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test4:Thread-4成功
13:33:06.066 [Thread-14] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test14:Thread-14成功
13:33:06.066 [Thread-1] INFO com.yisu.hystrix.without.FwHystrixCommondSemaphore - test1:Thread-1成功