Hystrix隔离策略

　　 Hystrix提供了两种隔离的解决方案：线程隔离和信号量隔离，默认为线程隔离。

private static final ExecutionIsolationStrategy default_executionIsolationStrategy = ExecutionIsolationStrategy.THREAD;

  public static enum ExecutionIsolationStrategy {         THREAD, SEMAPHORE     }

　　思路：请求被传入单独的线程池进行处理；
　　优点：存在超时机制；
　　缺点：线程切换和调度存在一定开销；

package com.cainiao.test.test.hystrix;  import com.netflix.hystrix.HystrixCommand; import com.netflix.hystrix.HystrixCommandGroupKey; import com.netflix.hystrix.HystrixCommandKey; import com.netflix.hystrix.HystrixCommandProperties; import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy; import com.netflix.hystrix.HystrixThreadPoolKey; import com.netflix.hystrix.HystrixThreadPoolProperties;  public class CommandHelloWorld extends HystrixCommand<Void> {      public CommandHelloWorld() {         super(HystrixCommand.Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("g1"))                 .andCommandKey(HystrixCommandKey.Factory.asKey("k1"))                 // 设置线程池属性                 .andThreadPoolKey(HystrixThreadPoolKey.Factory.asKey("ThreadPool"))                 .andThreadPoolPropertiesDefaults(HystrixThreadPoolProperties.Setter().withCoreSize(5)                         .withKeepAliveTimeMinutes(60).withMaxQueueSize(5).withQueueSizeRejectionThreshold(2))                 .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()                         // 开启熔断机制                         .withCircuitBreakerEnabled(true)                         // 熔断器开启3s后关闭                         .withCircuitBreakerSleepWindowInMilliseconds(3000)                         // 设置隔离策略                         .withExecutionIsolationStrategy(ExecutionIsolationStrategy.THREAD)));     }      @Override     protected Void run() {         System.out.println("Hello world!");         return null;     }  }

　　思路：请求被调用前，首先获取信号量，只有获得信号量的请求才会被处理；
　　优点：没有线程切换的开销；
　　缺点：没有超时机制；

package com.cainiao.test.test.hystrix;  import com.netflix.hystrix.HystrixCommand; import com.netflix.hystrix.HystrixCommandGroupKey; import com.netflix.hystrix.HystrixCommandKey; import com.netflix.hystrix.HystrixCommandProperties; import com.netflix.hystrix.HystrixCommandProperties.ExecutionIsolationStrategy;  public class CommandHelloWorld extends HystrixCommand<Void> {      public CommandHelloWorld() {         super(HystrixCommand.Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("g1"))                 .andCommandKey(HystrixCommandKey.Factory.asKey("k1"))                 .andCommandPropertiesDefaults(HystrixCommandProperties.Setter()                         // 开启熔断机制                         .withCircuitBreakerEnabled(true)                         // 熔断器开启3s后关闭                         .withCircuitBreakerSleepWindowInMilliseconds(3000)                         // 设置隔离策略                         .withExecutionIsolationStrategy(ExecutionIsolationStrategy.SEMAPHORE)));     }      @Override     protected Void run() {         System.out.println("Hello world!");         return null;     }  }

The advantage of the thread pool approach is that requests that are passed to C can be timed out, something that is not possible when using semaphores.

参考：

1. https://stackoverflow.com/questions/30391809/what-is-bulkhead-pattern-used-by-hystrix；
2. https://github.com/Netflix/Hystrix/wiki/How-it-Works#Isolation；

文章来源: Hystrix隔离策略