okhttp之Dispatcher

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base on 3.12.0

简介

首先我们来介绍下 Dispatcher，官方描述是这样的：

Policy on when async requests are executed. 执行异步请求时的策略

所以Dispatcher是我们进行异步请求是 okhttp 给我们提供的 执行异步请求时的策略.

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public final class Dispatcher {...}

我们可以看到 Dispatcher 类是由 final 修饰的，代表它不能被继承。

我们先来看下 Dispatcher是什么时候设置的。通过查看下面 OkHttpClient 的代码，我们知道在我们创建 OkHttpClient 的时候，如果我们没有通过 builder.dispatcher(Dispatcher dispatcher) 修改 Dispatcher的配置的话，默认的 dispatcher 就是默认配置的 Dispatcher类。

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public class OkHttpClient implements ... {
    ...
    public Builder newBuilder() {
        return new Builder(this);
    }
    public static final class Builder {
        Dispatcher dispatcher;
        ...
        public Builder() {
            dispatcher = new Dispatcher();
            ...
        }
        public Builder dispatcher(Dispatcher dispatcher) {
            if (dispatcher == null) throw new IllegalArgumentException("dispatcher == null");
            this.dispatcher = dispatcher;
            return this;
        }
    }
}

Dispatcher成员变量介绍

int maxRequests = 64; 默认同时执行的最大请求数，可以通过setMaxRequests(int)修改.
int maxRequestsPerHost = 5; 每个主机默认请求的最大数目，可以通过setMaxRequestsPerHost(int)修改.
private @Nullable Runnable idleCallback; 调度没有请求任务时的回调.
ExecutorService executorService; 执行异步请求的线程池，默认是核心线程为0，最大线程数为Integer.MAX_VALUE，空闲等待为60s.
Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>(); 异步请求的执行顺序的队列.
Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>(); 运行中的异步请求队列.
Deque<RealCall> runningSyncCalls = new ArrayDeque<>(); 运行中的同步请求队列.

Dispatcher构造函数

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public Dispatcher(ExecutorService executorService) {
  this.executorService = executorService;
}
public Dispatcher() {}

可以自己设置执行任务的线程池。

Dispatcher主要方法介绍

配置和获取同时执行请求的最大任务数、同主机允许同时执行的最大任务数

代码语言：javascript复制

public void setMaxRequests(int maxRequests) {...}
public synchronized int getMaxRequests() {...}
public void setMaxRequestsPerHost(int maxRequestsPerHost) {...}
public synchronized int getMaxRequestsPerHost() {...}

设置没有请求任务时的回调

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public synchronized void setIdleCallback(@Nullable Runnable idleCallback) {
    this.idleCallback = idleCallback;
}

添加到请求队列

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void enqueue(AsyncCall call) {
    synchronized (this) {
        readyAsyncCalls.add(call);
    }
    promoteAndExecute();
}
synchronized void executed(RealCall call) {
    runningSyncCalls.add(call);
}

执行等待队列中的请求任务

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private boolean promoteAndExecute() {
    assert (!Thread.holdsLock(this));
    List<AsyncCall> executableCalls = new ArrayList<>();
    boolean isRunning;
    synchronized (this) {
        //获取等待中的任务队列
        for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
            AsyncCall asyncCall = i.next();
            // 超过可以同时运行的最大请求任务数
            if (runningAsyncCalls.size() >= maxRequests) break; 
            // 超过同一主机同时运行的最大请求任务数
            if (runningCallsForHost(asyncCall) >= maxRequestsPerHost) continue; 
            i.remove();
            executableCalls.add(asyncCall);
            runningAsyncCalls.add(asyncCall);
        }
        isRunning = runningCallsCount() > 0;
    }
    for (int i = 0, size = executableCalls.size(); i < size; i  ) {
        AsyncCall asyncCall = executableCalls.get(i);
        asyncCall.executeOn(executorService());
    }
    return isRunning;
}

获取执行任务的线程池. 如果没有通过构造方法Dispatcher(ExecutorService executorService) 设置线程池的话，默认就是核心线程为0，最大线程数为Integer.MAX_VALUE，空闲等待为60s，用SynchronousQueue保存等待任务的线程池。

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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;
}

获取和当前请求的host一样的运行中的请求个数.

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private int runningCallsForHost(AsyncCall call) {
    int result = 0;
    for (AsyncCall c : runningAsyncCalls) {
        if (c.get().forWebSocket) continue;
        if (c.host().equals(call.host())) result  ;
    }
    return result;
}

取消所有请求任务

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public synchronized void cancelAll() {
    for (AsyncCall call : readyAsyncCalls) {
        call.get().cancel();
    }
    for (AsyncCall call : runningAsyncCalls) {
        call.get().cancel();
    }
    for (RealCall call : runningSyncCalls) {
        call.cancel();
    }
}

结束请求任务

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void finished(AsyncCall call) {}
void finished(RealCall call) {}
private <T> void finished(Deque<T> calls, T call) {
    Runnable idleCallback;
    synchronized (this) {
        if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
        idleCallback = this.idleCallback;
    }
    boolean isRunning = promoteAndExecute();

    if (!isRunning && idleCallback != null) {
        idleCallback.run();
    }
}

获取等待中、执行中的请求任务

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public synchronized List<Call> queuedCalls() {
    List<Call> result = new ArrayList<>();
    for (AsyncCall asyncCall : readyAsyncCalls) {
        result.add(asyncCall.get());
    }
    return Collections.unmodifiableList(result);
}
public synchronized List<Call> runningCalls() {
    List<Call> result = new ArrayList<>();
    result.addAll(runningSyncCalls);
    for (AsyncCall asyncCall : runningAsyncCalls) {
        result.add(asyncCall.get());
    }
    return Collections.unmodifiableList(result);
}
public synchronized int queuedCallsCount() {
    return readyAsyncCalls.size();
}
public synchronized int runningCallsCount() {
    return runningAsyncCalls.size()   runningSyncCalls.size();
}

小结

Dispatcher是我们进行异步请求是 okhttp 给我们提供的 执行异步请求时的策略。

Dispatcher因为是final修饰的类，所以我们我不能继承它，但是我们可以通过创建一个Dispatcher对象，然后修改 执行任务的线程池、 最大并发数、 同主机最大并发数 等。

执行任务的方法是promoteAndExecute().

以上

dispatcher executorservice int integer okhttp

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okhttp之Dispatcher

目录

简介

Dispatcher成员变量介绍

Dispatcher构造函数

Dispatcher主要方法介绍

小结