3.Okhttp3架构分析,主要通过一些流程图类展现
2.Okhttp主流程源码分析
1.okhttp的基本使用
=============
3.Okhttp3架构分析,主要通过一些流程图类展现
在OkHttp3中,其灵活性很大程度上体现在,可以intercept其任意一个环节,而这个优势便是okhttp3整个请求响应架构体系的精髓所在:
- 在OkHttp3中,每一个请求任务都封装为一个Call,其实现为RealCall。
- 而所有的策略几乎都可以通过OkHttpClient传入
- 所有全局策略与数据,除了存储在允许上层访问的OkHttpClient实例以外,还有一部分是存储在只允许包可见的Internal.instance中(如连接池、路由黑名单等)
- OkHttp中用户可传入的interceptor分为两类,一类是全局interceptor,该类interceptor在请求开始之前最早被调用,另外一类为非网页请求的networkInterceptor,这类interceptor只有在非网页请求中会被调用,并且是在组装完成请求之后,真正发起请求之前被调用(这块具体可以参看RealCall#getResponseWithInterceptorChain()方法)
- 整个请求过程通过RealInterceptorChain#proceed来连接,在每个interceptor中调用下一个interceptor来完成整个请求流程,并且在回到当前interceptor后完成响应处理
- 在异步请求中,我们通过Callback来获得简单清晰的请求回调(onFailure、onResponse)
- 在OkHttpClient中,我们可以传入EventListener的工厂方法,为每一个请求创建一个EventListener,来接收非常细的事件回调
OkHttp3中的线程池
OkHttp
中的对所有的任务采用 NamedRunnable
,约束每个执行单元给出对应的业务名称,以便于线程维护。
1.异步请求线程池-OkHttp Dispatcher
public synchronized ExecutorService executorService() { if (executorService == null) { executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false)); } return executorService; }
- 该线程池与Android下的
Executors.newCachedThreadPool()
比较类似; - 无任务上限,自动回收闲置60s的线程,适用于大量耗时较短的任务;
- 虽然线程池无任务上限,但是Dispatcher对入口
enqueue()
进行了把关,最大的异步任务数默认是64,同一个主机默认是5,当然这两个默认值是可以修改的,Dispatcher提供的修改接口;
okHttpClient.dispatcher().setMaxRequests(128); okHttpClient.dispatcher().setMaxRequestsPerHost(10);
-
通过两个双端队列来维护准备执行的任务和正在执行的任务:
Deque<AsyncCall> readyAsyncCalls
,Deque<AsyncCall> runningAsyncCalls
; -
在每个任务结束时,都会检查
readyAsyncCalls
是否有任务,在条件满足的情况下,按照先进先出的原则将任务移动到runningAsyncCalls
中,并在线程池中执行;
2.连接池清理线程池-OkHttp ConnectionPool
/**
* Background threads are used to cleanup expired connections. There will be at most a single
* thread running per connection pool. The thread pool executor permits the pool itself to be
* garbage collected.
*/
private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */, Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true));
- 该线程池用来清理长时间闲置的和泄漏的连接;
- 该线程池本身无任务上限,线程闲置60s自动回收;
- 虽然任务无上限,但其通过
cleanupRunning
标记来控制只有一个线程在运行,当连接池中没有连接后才会被重新设置为false
;
void put(RealConnection connection) { assert (Thread.holdsLock(this)); if (!cleanupRunning) { cleanupRunning = true; executor.execute(cleanupRunnable); } connections.add(connection); }
-
次工作线程会不断地清理,当清理完一遍后超时连接后,根据当前连接池中最近的下一个空闲超时连接计算出一个阻塞时间并阻塞,直到连接池中没有任何连接才结束,并将
cleanupRunning
设为false
; -
在每次有连接加入连接池时,如果当前没有清理任务运行,会加入一个清理任务到到线程池中执行;
void put(RealConnection connection) { assert (Thread.holdsLock(this)); if (!cleanupRunning) { cleanupRunning = true; executor.execute(cleanupRunnable); } connections.add(connection); }
3. 缓存整理线程池-OkHttp DiskLruCache
// Use a single background thread to evict entries.
Executor executor = new ThreadPoolExecutor(0, 1, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), Util.threadFactory("OkHttp DiskLruCache", true));
- 该线程池用于整理本地请求缓存数据;
- 缓存的整理包含: 达到阀值大小的文件,删除最近最少使用的记录,在有关操作达到一定数量以后对记录进行重建;
- 最大运行线程数1,无需考虑线程安全问题,自动回收闲置60s的线程;
4. HTTP2异步事务线程池-OkHttp Http2Connection
- HTTP2采用了多路复用,因此需要维护连接有效性,本线程池就是用于维护相关的各类HTTP2事务;
- 线程池本身无任务上限,自动回收闲置60s的线程;
- 每一个HTTP2连接都有这么一个线程池存在;
2.Okhttp主流程源码分析
在OkHttp3中,其灵活性很大程度上体现在可以 intercept
其任意一个环节,而这个优势便是okhttp3整个请求响应架构体系的精髓所在,先放出一张主框架请求流程图,接着再分析源码。
String url = "http://wwww.baidu.com";
OkHttpClient okHttpClient = new OkHttpClient(); final Request request = new Request.Builder() .url(url) .build(); Call call = okHttpClient.newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.d(TAG, "onFailure: "); } @Override public void onResponse(Call call, Response response) throws IOException { Log.d(TAG, "onResponse: " + response.body().string()); } });
这大概是一个最简单的一个例子了,在new OkHttpClient()
内部使用构造器模式初始化了一些配置信息:支持协议、任务分发器(其内部包含一个线程池,执行异步请求)、连接池(其内部包含一个线程池,维护connection)、连接/读/写超时时长等信息。
public Builder() { dispatcher = new Dispatcher(); //任务调度器 protocols = DEFAULT_PROTOCOLS; //支持的协议 connectionSpecs = DEFAULT_CONNECTION_SPECS; eventListenerFactory = EventListener.factory(EventListener.NONE); proxySelector = ProxySelector.getDefault(); cookieJar = CookieJar.NO_COOKIES; socketFactory = SocketFactory.getDefault(); hostnameVerifier = OkHostnameVerifier.INSTANCE; certificatePinner = CertificatePinner.DEFAULT; proxyAuthenticator = Authenticator.NONE; authenticator = Authenticator.NONE; connectionPool = new ConnectionPool(); //连接池 dns = Dns.SYSTEM; followSslRedirects = true; followRedirects = true; retryOnConnectionFailure = true; connectTimeout = 10_000;//超时时间 readTimeout = 10_000; writeTimeout = 10_000; pingInterval = 0; }
第一行创建了一个Dispatcher
任务调度器,它定义了三个双向任务队列,两个异步队列:准备执行的请求队列 readyAsyncCalls
、正在运行的请求队列 runningAsyncCalls
;一个正在运行的同步请求队列 runningSyncCalls
;
public final class Dispatcher { private int maxRequests = 64; //最大请求数量 private int maxRequestsPerHost = 5; //每台主机最大的请求数量 private @Nullable Runnable idleCallback; /** Executes calls. Created lazily. */ private @Nullable ExecutorService executorService; //线程池 /** Ready async calls in the order they'll be run. */ private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>(); /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */ private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>(); /** Running synchronous calls. Includes canceled calls that haven't finished yet. */ private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>(); /** 这个线程池没有核心线程,线程数量没有限制,空闲60s就会回收*/ public synchronized ExecutorService executorService() { if (executorService == null) { executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false)); } return executorService; } }
另外还有一个线程池 executorService
,这个线程池跟Android中的CachedThreadPool非常类似,这种类型的线程池,适用于大量的耗时较短的异步任务。下一篇文章 将对OkHttp框架中的线程池做一个总结。
接下来接着看Request的构造,这个例子Request比较简单,指定了请求方式 GET
和请求 url
public static class Builder { HttpUrl url; String method; Headers.Builder headers; RequestBody body; Object tag; public Builder() { this.method = "GET"; this.headers = new Headers.Builder(); } public Builder url(HttpUrl url) { if (url == null) throw new NullPointerException("url == null"); this.url = url; return this; } public Request build() { if (url == null) throw new IllegalStateException("url == null"); return new Request(this); } ... }
紧接着通过 OkHttpClient
和 Request
构造一个 Call
对象,它的实现是RealCall
public Call newCall(Request request) { return RealCall.newRealCall(this, request, false /* for web socket */); } static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket){ // Safely publish the Call instance to the EventListener. RealCall call = new RealCall(client, originalRequest, forWebSocket); call.eventListener = client.eventListenerFactory().create(call); return call; } private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) { this.client = client; this.originalRequest = originalRequest; this.forWebSocket = forWebSocket; this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket); }
可以看到在 RealCall
的构造方法中创建了一个RetryAndFollowUpInterceptor
,用于处理请求错误和重定向等,这是 Okhttp
框架的精髓 interceptor chain
中的一环,默认情况下也是第一个拦截器,除非调用 OkHttpClient.Builder#addInterceptor(Interceptor)
来添加全局的拦截器。关于拦截器链的顺序参见 RealCall#getResponseWithInterceptorChain()
方法。
RealCall#enqueue(Callback)
public void enqueue(Callback responseCallback) { synchronized (this) { //每个请求只能之执行一次 if (executed) throw new IllegalStateException("Already Executed"); executed = true; } captureCallStackTrace(); eventListener.callStart(this); client.dispatcher().enqueue(new AsyncCall(responseCallback)); }
可以看到,一个 Call
只能执行一次,否则会抛异常,这里创建了一个 AsyncCall
并将Callback传入,接着再交给任务分发器 Dispatcher
来进一步处理。
synchronized void enqueue(AsyncCall call) { //正在执行的任务数量小于最大值(64),并且此任务所属主机的正在执行任务小于最大值(5) if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) { runningAsyncCalls.add(call); executorService().execute(call); } else { readyAsyncCalls.add(call); } }
从 Dispatcher#enqueue()
方法的策略可以看出,对于请求的入队做了一些限制,若正在执行的请求数量小于最大值(默认64),并且此请求所属主机的正在执行任务小于最大值(默认5),就加入正在运行的队列并通过线程池来执行该任务,否则加入准备执行队列中。
- 流程图
现在回头看看 AsyncCall
,它继承自 NamedRunnable
,而 NamedRunnable
实现了 Runnable
接口,它的作用有2个:
①采用模板方法的设计模式,让子类将具体的操作放在 execute()
方法中;
②给线程指定一个名字,比如传入模块名称,方便监控线程的活动状态;
public abstract class NamedRunnable implements Runnable { protected final String name; public NamedRunnable(String format, Object... args) { this.name = Util.format(format, args); } @Override public final void run() { String oldName = Thread.currentThread().getName(); Thread.currentThread().setName(name); try { //采用模板方法让子类将具体的操作放到此execute()方法 execute(); } finally { Thread.currentThread().setName(oldName); } } protected abstract void execute(); }
final class AsyncCall extends NamedRunnable { //省略... @Override protected void execute() { boolean signalledCallback = false; try { //调用 getResponseWithInterceptorChain()获得响应内容 Response response = getResponseWithInterceptorChain(); //① if (retryAndFollowUpInterceptor.isCanceled()) { //这个标记为主要是避免异常时2次回调 signalledCallback = true; //回调Callback告知失败 responseCallback.onFailure(RealCall.this, new IOException("Canceled")); } else { signalledCallback = true; //回调Callback,将响应内容传回去 responseCallback.onResponse(RealCall.this, response); } } catch (IOException e) { if (signalledCallback) { // Do not signal the callback twice! Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e); } else { eventListener.callFailed(RealCall.this, e); responseCallback.onFailure(RealCall.this, e); } } finally { //不管请求成功与否,都进行finished()操作 client.dispatcher().finished(this);//② } } }
先看注释②的行finally块中执行的 client.dispatcher().finished(this)
void finished(AsyncCall call) { finished(runningAsyncCalls, call, true); } private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) { int runningCallsCount; Runnable idleCallback; synchronized (this) { //从正在执行的队列中将其移除 if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!"); if (promoteCalls) promoteCalls(); //推动下一个任务的执行 runningCallsCount = runningCallsCount();//同步+异步的正在执行任务数量 idleCallback = this.idleCallback; } //如果没有正在执行的任务,且idleCallback不为null,则回调通知空闲了 if (runningCallsCount == 0 && idleCallback != null) { idleCallback.run(); } }
其中promoteCalls()
为推动下一个任务执行,其实它做的也很简单,就是在条件满足的情况下,将 readyAsyncCalls
中的任务移动到 runningAsyncCalls
中,并交给线程池来执行,以下是它的实现。
private void promoteCalls() { if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity. if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote. //若条件允许,将readyAsyncCalls中的任务移动到runningAsyncCalls中,并交给线程池执行 for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) { AsyncCall call = i.next(); if (runningCallsForHost(call) < maxRequestsPerHost) { i.remove(); runningAsyncCalls.add(call); executorService().execute(call); } //当runningAsyncCalls满了,直接退出迭代 if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity. } }
接下来就回到注释①处的响应内容的获取 getResponseWithInterceptorChain()
Response getResponseWithInterceptorChain() throws IOException { // Build a full stack of interceptors. List<Interceptor> interceptors = new ArrayList<>(); //这是一个List,是有序的 interceptors.addAll(client.interceptors());//首先添加的是用户添加的全局拦截器 interceptors.add(retryAndFollowUpInterceptor); //错误、重定向拦截器 //桥接拦截器,桥接应用层与网络层,添加必要的头、 interceptors.add(new BridgeInterceptor(client.cookieJar())); //缓存处理,Last-Modified、ETag、DiskLruCache等 interceptors.add(new CacheInterceptor(client.internalCache())); //连接拦截器 interceptors.add(new ConnectInterceptor(client)); //从这就知道,通过okHttpClient.Builder#addNetworkInterceptor()传进来的拦截器只对非网页的请求生效 if (!forWebSocket) { interceptors.addAll(client.networkInterceptors()); } //真正访问服务器的拦截器 interceptors.add(new CallServerInterceptor(forWebSocket)); Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0, originalRequest, this, eventListener, client.connectTimeoutMillis(), client.readTimeoutMillis(), client.writeTimeoutMillis()); return chain.proceed(originalRequest); }
可以看这块重点就是 interceptors
这个集合,首先将前面的 client.interceptors()
全部加入其中,还有在创建 RealCall
时的 retryAndFollowUpInterceptor
加入其中,接着还创建并添加了BridgeInterceptor、CacheInterceptor、ConnectInterceptor、CallServerInterceptor
,最后通过RealInterceptorChain#proceed(Request)
来执行整个 interceptor chain
,可见把这个拦截器链搞清楚,整体流程也就明朗了。
RealInterceptorChain#proceed()
public Response proceed(Request request) throws IOException { return proceed(request, streamAllocation, httpCodec, connection); } public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec, RealConnection connection) throws IOException { //省略异常处理... // Call the next interceptor in the chain. RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec, connection, index + 1, request, call, eventListener, connectTimeout, readTimeout, writeTimeout); Interceptor interceptor = interceptors.get(index); Response response = interceptor.intercept(next); //省略异常处理... return response; }
从这段实现可以看出,是按照添加到 interceptors
集合的顺序,逐个往下调用拦截器的intercept()方法,所以在前面的拦截器会先被调用。这个例子中自然就是 RetryAndFollowUpInterceptor
了。
public Response intercept(Chain chain) throws IOException { Request request = chain.request(); RealInterceptorChain realChain = (RealInterceptorChain) chain; Call call = realChain.call(); EventListener eventListener = realChain.eventListener(); //创建一个StreamAllocation StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(), createAddress(request.url()), call, eventListener, callStackTrace); this.streamAllocation = streamAllocation; //统计重定向次数,不能大于20 int followUpCount = 0; Response priorResponse = null; while (true) { if (canceled) { streamAllocation.release(); throw new IOException("Canceled"); } Response response; boolean releaseConnection = true; try { //调用下一个interceptor的来获得响应内容 response = realChain.proceed(request, streamAllocation, null, null); releaseConnection = false; } catch (RouteException e) { // The attempt to connect via a route failed. The request will not have been sent. if (!recover(e.getLastConnectException(), streamAllocation, false, request)) { throw e.getLastConnectException(); } releaseConnection = false; continue; } catch (IOException e) { // An attempt to communicate with a server failed. The request may have been sent. boolean requestSendStarted = !(e instanceof ConnectionShutdownException); if (!recover(e, streamAllocation, requestSendStarted, request)) throw e; releaseConnection = false; continue; } finally { // We're throwing an unchecked exception. Release any resources. if (releaseConnection) { streamAllocation.streamFailed(null); streamAllocation.release(); } } // Attach the prior response if it exists. Such responses never have a body. if (priorResponse != null) { response = response.newBuilder() .priorResponse(priorResponse.newBuilder() .body(null) .build()) .build(); } //重定向处理 Request followUp =