hystrix(5) 延时检测

　　hystrix在执行命令的同事，会对执行延时进行检测，如果超过设置的延时时间，那么将停止执行，并返回fallback执行结果。

if (properties.executionTimeoutEnabled().get()) {
            execution = executeCommandWithSpecifiedIsolation(_cmd)
                    .lift(new HystrixObservableTimeoutOperator<R>(_cmd));
        } else {
            execution = executeCommandWithSpecifiedIsolation(_cmd);
        }

　　本质就是开启一个定时器，当到达指定时间时，去检测执行命令是否完成，如果没有完成，则返回异常，外部方法监听异常，执行fallback。

private static class HystrixObservableTimeoutOperator<R> implements Operator<R, R> {
        final AbstractCommand<R> originalCommand;
        public HystrixObservableTimeoutOperator(final AbstractCommand<R> originalCommand) {
            this.originalCommand = originalCommand;
        }
        @Override
        public Subscriber<? super R> call(final Subscriber<? super R> child) {
            ...
            final HystrixContextRunnable timeoutRunnable = new HystrixContextRunnable(originalCommand.concurrencyStrategy, new Runnable() {
                @Override
                public void run() {
                    child.onError(new HystrixTimeoutException());
                }
            });
            TimerListener listener = new TimerListener() {
...
                        timeoutRunnable.run();
                    ...
                    }
                }
                @Override
                public int getIntervalTimeInMilliseconds() {
                    return originalCommand.properties.executionTimeoutInMilliseconds().get();
                }
            };
            final Reference<TimerListener> tl = HystrixTimer.getInstance().addTimerListener(listener);
           ...
        }

    }