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docs: Translate some of the README docs into Chinese (#1744)
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* docs: translated docs to zh

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Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>
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312 changes: 312 additions & 0 deletions zh/circuit-breaker/README.md
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---
layout: pattern
title: Circuit Breaker
folder: circuit-breaker
permalink: /patterns/circuit-breaker/
categories: Behavioral
tags:
- Performance
- Decoupling
- Cloud distributed
---

## 含义

以这样的方式(译者:指断路器方式)处理昂贵的远程服务调用,可以防止单个服务/组件的故障导致整个应用程序崩溃,同时我们可以尽快地进行服务重连。

## 解释

现实世界案例

> 设想一下,一个网络应用程序既有本地文件/图像,又有用于获取数据的远程服务。这些远程服务可能在某些时候是健康的、有反应的,也可能在某些时候由于各种原因而变得缓慢和无反应。因此,如果其中一个远程服务速度慢或不能成功响应,我们的应用程序将尝试使用多个线程/进程从远程服务中获取响应,很快所有的线程/进程都会挂起(也称为线程饥饿 thread starvation),从而导致我们整个 Web 应用程序崩溃。我们应该能够检测到这种情况,并向用户显示一个适当的信息,以便用户可以探索应用程序的其他部分,而不受远程服务故障的影响。同时,其他正常工作的服务应该保持运作,不受这次故障的影响。
简而言之

> 断路器允许优雅地处理失败的远程服务。当我们的应用程序的所有部分都高度解耦时,这种方式的效果会很好,一个组件的失败并不会导致其他部分停止工作。
维基百科的解释

> 断路器是现代软件开发中使用的一种设计模式。它用于检测故障,并封装了防止故障不断复发的逻辑,在维护期间,临时地处理外部系统故障或意外的系统问题。
## Programmatic Example

那么,这一切是如何实现的呢?考虑到上面的例子,我们将在一个简单的例子中模拟这个功能。一个监控服务(译者:下图的 Monitoring Service)模拟了网络应用,进行本地和远程调用。

该服务架构如下:

![alt text](../../circuit-breaker/etc/ServiceDiagram.png "Service Diagram")

终端用户(译者:上图的 End User)应用的代码如下:

```java
@Slf4j
public class App {

private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

/**
* Program entry point.
*
* @param args command line args
*/
public static void main(String[] args) {

var serverStartTime = System.nanoTime();

var delayedService = new DelayedRemoteService(serverStartTime, 5);
var delayedServiceCircuitBreaker = new DefaultCircuitBreaker(delayedService, 3000, 2,
2000 * 1000 * 1000);

var quickService = new QuickRemoteService();
var quickServiceCircuitBreaker = new DefaultCircuitBreaker(quickService, 3000, 2,
2000 * 1000 * 1000);

//Create an object of monitoring service which makes both local and remote calls
var monitoringService = new MonitoringService(delayedServiceCircuitBreaker,
quickServiceCircuitBreaker);

//Fetch response from local resource
LOGGER.info(monitoringService.localResourceResponse());

//Fetch response from delayed service 2 times, to meet the failure threshold
LOGGER.info(monitoringService.delayedServiceResponse());
LOGGER.info(monitoringService.delayedServiceResponse());

//Fetch current state of delayed service circuit breaker after crossing failure threshold limit
//which is OPEN now
LOGGER.info(delayedServiceCircuitBreaker.getState());

//Meanwhile, the delayed service is down, fetch response from the healthy quick service
LOGGER.info(monitoringService.quickServiceResponse());
LOGGER.info(quickServiceCircuitBreaker.getState());

//Wait for the delayed service to become responsive
try {
LOGGER.info("Waiting for delayed service to become responsive");
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//Check the state of delayed circuit breaker, should be HALF_OPEN
LOGGER.info(delayedServiceCircuitBreaker.getState());

//Fetch response from delayed service, which should be healthy by now
LOGGER.info(monitoringService.delayedServiceResponse());
//As successful response is fetched, it should be CLOSED again.
LOGGER.info(delayedServiceCircuitBreaker.getState());
}
}
```

监控服务代码(译者:上图的 monitoring service):

```java
public class MonitoringService {

private final CircuitBreaker delayedService;

private final CircuitBreaker quickService;

public MonitoringService(CircuitBreaker delayedService, CircuitBreaker quickService) {
this.delayedService = delayedService;
this.quickService = quickService;
}

//Assumption: Local service won't fail, no need to wrap it in a circuit breaker logic
public String localResourceResponse() {
return "Local Service is working";
}

/**
* Fetch response from the delayed service (with some simulated startup time).
*
* @return response string
*/
public String delayedServiceResponse() {
try {
return this.delayedService.attemptRequest();
} catch (RemoteServiceException e) {
return e.getMessage();
}
}

/**
* Fetches response from a healthy service without any failure.
*
* @return response string
*/
public String quickServiceResponse() {
try {
return this.quickService.attemptRequest();
} catch (RemoteServiceException e) {
return e.getMessage();
}
}
}
```
可以看出,它直接进行了获取本地资源的调用,但它把对远程(昂贵的)服务的调用包装在一个断路器对象中,这样可以防止出现如下故障:

```java
public class DefaultCircuitBreaker implements CircuitBreaker {

private final long timeout;
private final long retryTimePeriod;
private final RemoteService service;
long lastFailureTime;
private String lastFailureResponse;
int failureCount;
private final int failureThreshold;
private State state;
private final long futureTime = 1000 * 1000 * 1000 * 1000;

/**
* Constructor to create an instance of Circuit Breaker.
*
* @param timeout Timeout for the API request. Not necessary for this simple example
* @param failureThreshold Number of failures we receive from the depended service before changing
* state to 'OPEN'
* @param retryTimePeriod Time period after which a new request is made to remote service for
* status check.
*/
DefaultCircuitBreaker(RemoteService serviceToCall, long timeout, int failureThreshold,
long retryTimePeriod) {
this.service = serviceToCall;
// We start in a closed state hoping that everything is fine
this.state = State.CLOSED;
this.failureThreshold = failureThreshold;
// Timeout for the API request.
// Used to break the calls made to remote resource if it exceeds the limit
this.timeout = timeout;
this.retryTimePeriod = retryTimePeriod;
//An absurd amount of time in future which basically indicates the last failure never happened
this.lastFailureTime = System.nanoTime() + futureTime;
this.failureCount = 0;
}

// Reset everything to defaults
@Override
public void recordSuccess() {
this.failureCount = 0;
this.lastFailureTime = System.nanoTime() + futureTime;
this.state = State.CLOSED;
}

@Override
public void recordFailure(String response) {
failureCount = failureCount + 1;
this.lastFailureTime = System.nanoTime();
// Cache the failure response for returning on open state
this.lastFailureResponse = response;
}

// Evaluate the current state based on failureThreshold, failureCount and lastFailureTime.
protected void evaluateState() {
if (failureCount >= failureThreshold) { //Then something is wrong with remote service
if ((System.nanoTime() - lastFailureTime) > retryTimePeriod) {
//We have waited long enough and should try checking if service is up
state = State.HALF_OPEN;
} else {
//Service would still probably be down
state = State.OPEN;
}
} else {
//Everything is working fine
state = State.CLOSED;
}
}

@Override
public String getState() {
evaluateState();
return state.name();
}

/**
* Break the circuit beforehand if it is known service is down Or connect the circuit manually if
* service comes online before expected.
*
* @param state State at which circuit is in
*/
@Override
public void setState(State state) {
this.state = state;
switch (state) {
case OPEN:
this.failureCount = failureThreshold;
this.lastFailureTime = System.nanoTime();
break;
case HALF_OPEN:
this.failureCount = failureThreshold;
this.lastFailureTime = System.nanoTime() - retryTimePeriod;
break;
default:
this.failureCount = 0;
}
}

/**
* Executes service call.
*
* @return Value from the remote resource, stale response or a custom exception
*/
@Override
public String attemptRequest() throws RemoteServiceException {
evaluateState();
if (state == State.OPEN) {
// return cached response if the circuit is in OPEN state
return this.lastFailureResponse;
} else {
// Make the API request if the circuit is not OPEN
try {
//In a real application, this would be run in a thread and the timeout
//parameter of the circuit breaker would be utilized to know if service
//is working. Here, we simulate that based on server response itself
var response = service.call();
// Yay!! the API responded fine. Let's reset everything.
recordSuccess();
return response;
} catch (RemoteServiceException ex) {
recordFailure(ex.getMessage());
throw ex;
}
}
}
}
```

上述模式是如何防止失败的呢?让我们通过它所实现的这个有限状态机来了解。

![alt text](../../circuit-breaker/etc/StateDiagram.png "State Diagram")

- 我们用 `timeout`(超时)、 `failureThreshold` (失败阈值)、`retryTimePeriod`(重试时间周期) 参数初始化断路器对象 ,用于确定 API 的适应性。
- 最初,断路器处于 `closed` 关闭状态,没有发生对 API 的远程调用。
- 每次调用成功,我们就把状态重置为开始时的样子。
- 如果失败的次数超过了一定的阈值(`failureThreshold`),断路器就会进入 `open` 开启状态,它的作用就像一个开启的电路,阻止远程服务的调用,从而节省资源。
- 一旦我们超过重试时间周期(`retryTimePeriod`),断路器就会转到 `half-open` 半启用状态,并再次调用远程服务,检查服务是否正常,以便我们可以提供最新的响应内容。如果远程服务调用失败会使断路器回到 `open` 状态,并在重试超时后进行另一次尝试;如果远程服务调用成功则使断路器进入 `closed` 状态,这样一切又开始正常工作。

## 类图

![alt text](../../circuit-breaker/etc/circuit-breaker.urm.png "Circuit Breaker class diagram")

## 适用场景

在以下场景下,可以使用断路器模式:

- 构建一个高可用的应用程序,某些些服务的失败不会导致整个应用程序的崩溃。
- 构建一个持续运行(长期在线)的应用程序,以便其组件可以在不完全关闭的情况下进行升级。

## 相关模式

- [Retry Pattern](https://github.com/iluwatar/java-design-patterns/tree/master/retry)

## 现实案例

* [Spring Circuit Breaker module](https://spring.io/guides/gs/circuit-breaker)
* [Netflix Hystrix API](https://github.com/Netflix/Hystrix)

## 引用

* [Understanding Circuit Breaker Pattern](https://itnext.io/understand-circuitbreaker-design-pattern-with-simple-practical-example-92a752615b42)
* [Martin Fowler on Circuit Breaker](https://martinfowler.com/bliki/CircuitBreaker.html)
* [Fault tolerance in a high volume, distributed system](https://medium.com/netflix-techblog/fault-tolerance-in-a-high-volume-distributed-system-91ab4faae74a)
* [Circuit Breaker pattern](https://docs.microsoft.com/en-us/azure/architecture/patterns/circuit-breaker)
29 changes: 29 additions & 0 deletions zh/collection-pipeline/README.md
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---
layout: pattern
title: Collection Pipeline
folder: collection-pipeline
permalink: /patterns/collection-pipeline/
categories: Functional
tags:
- Reactive
---

## 释义
**集合管道(Collection Pipeline)**包含**函数组合(Function Composition)****集合管道(Collection Pipeline)**两组合概念,这是两种函数式编程模式,你可以在代码中结合这两种模式来进行集合迭代。
在函数式编程中,可以通过一系列较小的模块化函数或操作来编排复杂的操作。这一系列函数被称为函数组合。当一个数据集合流经一个函数组合时,它就成为一个集合管道。函数组合和集合管道是函数式编程中经常使用的两种设计模式。

## 类图
![alt text](../../collection-pipeline/etc/collection-pipeline.png "Collection Pipeline")

## 适用场景
在以下场景适用集合管道模式:

* 当你想执行一组连续的算子操作,其中一个算子收集的输出需要被输入到下一个算子中
* 当你在代码中需要使用大量的中间状态语句时
* 当你在代码中使用大量的循环语句时

## 引用

* [Function composition and the Collection Pipeline pattern](https://www.ibm.com/developerworks/library/j-java8idioms2/index.html)
* [Martin Fowler](https://martinfowler.com/articles/collection-pipeline/)
* [Java8 Streams](https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html)

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