1.正在执行的任务数量最大值是64

 异步请求放入readyAsyncCalls后，遍历readyAsyncCalls取出任务去执行的时候，如果发现runningAsyncCalls的数量大于等于64，就不从readyAsyncCalls取出任务执行。

public final class Dispatcher {private int maxRequests = 64;private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();private boolean promoteAndExecute() {assert (!Thread.holdsLock(this));List<AsyncCall> executableCalls = new ArrayList<>();boolean isRunning;synchronized (this) {for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {AsyncCall asyncCall = i.next();//如果超过了最大数目if (runningAsyncCalls.size() >= maxRequests) break; // Max capacity.if (asyncCall.callsPerHost().get() >= maxRequestsPerHost) continue; // Host max capacity.//从readyAsyncCalls removei.remove();//callsPerHost+1asyncCall.callsPerHost().incrementAndGet();//添加到executableCallsexecutableCalls.add(asyncCall);//添加到runningAsyncCallsrunningAsyncCalls.add(asyncCall);}isRunning = runningCallsCount() > 0;}for (int i = 0, size = executableCalls.size(); i < size; i++) {AsyncCall asyncCall = executableCalls.get(i);//执行asyncCall.executeOn(executorService());}return isRunning;}
}

2.同一个主机的最大连接数为5

异步请求放入readyAsyncCalls后，遍历readyAsyncCalls取出任务去执行的时候，如果发现asyncCall的callsPerHost大于等于5，就不从readyAsyncCalls取出任务执行；否则callsPerHost加1。

public final class Dispatcher {private int maxRequestsPerHost = 5; //默认5。这是okhttp对同一主机允许的最大请求数量。void enqueue(AsyncCall call) {synchronized (this) {readyAsyncCalls.add(call);//Mutate the AsyncCall so that it shares the AtomicInteger //of an existing running call to the same host.if (!call.get().forWebSocket) {//从已经存在的任务里面找同一个主机的任务AsyncCall existingCall = findExistingCallWithHost(call.host());if (existingCall != null) {//call的将callsPerHost赋值为existingCall的callsPerHostcall.reuseCallsPerHostFrom(existingCall);}}}promoteAndExecute();}//有个疑问，这里是不是要从ArrayDeque尾向前获取，才能获取到最新的AsyncCall，这样获取到的//callsPerHost才会是最大的？//目前从头开始获取，是不是有问题？//先从runningAsyncCalls找，再从readyAsyncCalls找@Nullable private AsyncCall findExistingCallWithHost(String host) {for (AsyncCall existingCall : runningAsyncCalls) {if (existingCall.host().equals(host)) {return existingCall;}}for (AsyncCall existingCall : readyAsyncCalls) {if (existingCall.host().equals(host)) {return existingCall;}}return null;}
}