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);
...
}
}