public final class RouteSelector {
  /**
   * Clients should invoke this method when they encounter a connectivity failure on a connection
   * returned by this route selector.
   * 在StreamAllocation.streamFailed()中添加了routeSelector.connectFailed()逻辑
   */
  public void connectFailed(Route failedRoute, IOException failure) {
    if (failedRoute.proxy().type() != Proxy.Type.DIRECT && address.proxySelector() != null) {
      // Tell the proxy selector when we fail to connect on a fresh connection.
      address.proxySelector().connectFailed(
          address.url().uri(), failedRoute.proxy().address(), failure);
    }

    routeDatabase.failed(failedRoute);
  }
}

Dispatcher

Dispatcher(分离器或者复用器)是异步网络请求调用时执行的策略方法, 复用器的概念十分常见，它主要的作用是输入的各路信号进行卷积运算，最大可能压榨通信的带宽，提高信息传输的效率。Dispatcher控制最大请求并发数和单个主机的最大并发数，并持有一个线程池负责执行异步请求，对同步的请求只是用作统计。OkHttp在每个分离器使用一个ExecutorService内部调用请求, Dispatcher内部主要并不涉及执行的具体。

  synchronized void enqueue(AsyncCall call) {
    if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      runningAsyncCalls.add(call);
      executorService().execute(call);
    } else {
      readyAsyncCalls.add(call);
    }
  }

  ...
  /** Used by {@code Call#execute} to signal it is in-flight. */
  synchronized void executed(RealCall call) {
    runningSyncCalls.add(call);
  }

ExecutorSevice.execute(AsyncCall)执行代码位于AsyncCall内部复写的execute()方法, 方法内定义一些Callback回调节点运行逻辑，包括用户主动取消执行（使用retryAndFollowUpInterceptor）以及执行请求成功或者失败时的回调方法

final class AsyncCall extends NamedRunnable {
    ...
    @Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          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 {
        client.dispatcher().finished(this);
      }
    }
  }

• 惰性初始模式(Created Lazily)成员
  • ExecutorService()
  • CacheControl

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