【线上踩坑】Spring Cloud Hystrix线程池不足

现象：

昨天突然线上很多接口获取失败，通过 kibana发现大量异常，具体异常信息：

...into fallback. Rejected command because thread-pool queueSize is at rejection threshold.

异常代码出处：

@FeignClient(name = "api", fallbackFactory = LoadBalancingFallbackFactory.class)
public interface LoadBalancingFeignClient {

    @PostMapping(value = "/api/loadBalancing/server")
    Result currentServer();

}

@Slf4j
@Component
public class LoadBalancingFallbackFactory implements FallbackFactory<LoadBalancingFeignClient> {

    @Override
    public LoadBalancingFeignClient create(Throwable throwable) {
        final String msg = throwable.getMessage();
        return () -> {
            log.error("loadBalancingFeignClient currentServer into fallback. {}", msg);
            return Result.error();
        };****
    }

}复制代码

原因：

看到这里已经很明显了，是由于hystrix线程池不够用，直接熔断导致的。项目apollo配置：

hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds = 3500
hystrix.threadpool.default.maxQueueSize = 60
hystrix.threadpool.default.queueSizeRejectionThreshold = 40复制代码

hystrix参数简析：

maxQueueSize：线程池大小，默认为-1，创建的队列是SynchronousQueue，如果设置大于0则根据其大小创建LinkedBlockingQueue。

queueSizeRejectionThreshold：动态控制线程池队列的上限，即使maxQueueSize没有达到，达到queueSizeRejectionThreshold该值后，请求也会被拒绝，默认值5

相关源码：

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/strategy/concurrency/HystrixContextScheduler.java

    private class HystrixContextSchedulerWorker extends Worker {

        private final Worker worker;

        private HystrixContextSchedulerWorker(Worker actualWorker) {
            this.worker = actualWorker;
        }

        @Override
        public void unsubscribe() {
            worker.unsubscribe();
        }

        @Override
        public boolean isUnsubscribed() {
            return worker.isUnsubscribed();
        }

        @Override
        public Subscription schedule(Action0 action, long delayTime, TimeUnit unit) {
            if (threadPool != null) {
                if (!threadPool.isQueueSpaceAvailable()) {
                    throw new RejectedExecutionException("Rejected command because thread-pool queueSize is at rejection threshold.");
                }
            }
            return worker.schedule(new HystrixContexSchedulerAction(concurrencyStrategy, action), delayTime, unit);
        }

        @Override
        public Subscription schedule(Action0 action) {
            if (threadPool != null) {
                if (!threadPool.isQueueSpaceAvailable()) {
                    throw new RejectedExecutionException("Rejected command because thread-pool queueSize is at rejection threshold.");
                }
            }
            return worker.schedule(new HystrixContexSchedulerAction(concurrencyStrategy, action));
        }

    }复制代码

解决办法：

适当调大Hystrix线程队列参数
动态水平扩容服务
优化下游服务，减少服务响应时间

【线上踩坑】系列主要是用于简单记录工作中实际遇到的线上问题，如需要更深入的学习和了解，可以直接联系作者。

【线上踩坑】Spring Cloud Hystrix线程池不足

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