异步请求
一般的异步调用代码为
val enqueueResponse = OkHttpClient().newCall(request).enqueue(object: Callback {
override fun onFailure(call: Call, e: IOException) {
TODO("Not yet implemented")
}
override fun onResponse(call: Call, response: Response) {
TODO("Not yet implemented")
}
})
查看enqueue源码，在RealCall中实现
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
流程跟同步的没什么差别，我们直接看dispathcer中的enqueue
void enqueue(AsyncCall call) {
synchronized (this) {
readyAsyncCalls.add(call);
}
promoteAndExecute();
}
这里跟同步的也并没有什么差别，只是将请求加入了异步等待队列，我们在进入promoteAndExecute方法,从命名上看这个方法应该是校验和执行的方法
private boolean promoteAndExecute() {
assert (!Thread.holdsLock(this));
List executableCalls = new ArrayList<>();
boolean isRunning;
synchronized (this) {
for (Iterator i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall asyncCall = i.next();
if (runningAsyncCalls.size() >= maxRequests) break; // Max capacity.
if (runningCallsForHost(asyncCall) >= maxRequestsPerHost) continue; // Host max capacity.
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;
}
首先判断判断线程是否阻塞,创建一个AsyncCall对象的列表
对请求加锁
从队列中取出请求将请求添加进执行请求队列和异步执行队列runningAsyncCall中
然后将其放入executorService对象中执行
我们去查看executorService是什么
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
}
我们发现这里如果没有线程池的话，创建一个线程池并返回该线程池
我们在看看executeOn干了什么
void executeOn(ExecutorService executorService) {
assert (!Thread.holdsLock(client.dispatcher()));
boolean success = false;
try {
executorService.execute(this);
success = true;
} catch (RejectedExecutionException e) {
InterruptedIOException ioException = new InterruptedIOException("executor rejected");
ioException.initCause(e);
eventListener.callFailed(RealCall.this, ioException);
responseCallback.onFailure(RealCall.this, ioException);
} finally {
if (!success) {
client.dispatcher().finished(this); // This call is no longer running!
}
}
}
我们看到这里只是单纯的使用线程池执行而已
我们在去看看执行的核心代码
AsyncCall
查看源码
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
String host() {
return originalRequest.url().host();
}
Request request() {
return originalRequest;
}
RealCall get() {
return RealCall.this;
}
/**
* Attempt to enqueue this async call on {@code executorService}. This will attempt to clean up
* if the executor has been shut down by reporting the call as failed.
*/
void executeOn(ExecutorService executorService) {
assert (!Thread.holdsLock(client.dispatcher()));
boolean success = false;
try {
executorService.execute(this);
success = true;
} catch (RejectedExecutionException e) {
InterruptedIOException ioException = new InterruptedIOException("executor rejected");
ioException.initCause(e);
eventListener.callFailed(RealCall.this, ioException);
responseCallback.onFailure(RealCall.this, ioException);
} finally {
if (!success) {
client.dispatcher().finished(this); // This call is no longer running!
}
}
}
@Override protected void execute() {
boolean signalledCallback = false;
timeout.enter();
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) {
e = timeoutExit(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);
}
}
}
我们发现他是继承于NamedRunnable我们在去看看NamedRunnable是什么
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 {
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}
protected abstract void execute();
}
可以看到NamedRunnable是一个抽象类，我们直接看run方法，可以看到，这里将当前执行的线程的名字设为我们在构造方法中传入的名字，接着执行execute方法，finally再设置回来。所以我们在回到AsyCall找execute方法了。
@Override protected void execute() {
boolean signalledCallback = false;
timeout.enter();
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) {
e = timeoutExit(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);
}
}
}
看到了我们熟悉的Response对象和getResponseWithInterceptorChain方法,后续就是一些状态的回调，就不在分析了，异步的流程源码就分析到这了，后续在进几个默认的拦截器看看