前语

检查Okhttp源码时，在Transmitter类中发现了一个AsyncTimeout政策。了解代码后得知，该类是用于做一些超时检测的操作。本文首要总结笔者关于AsyncTimeout机制的研讨appstore。

本文基于okhttp 3.14.9

github地址：github.com/square/ookhttp3下载kht…

gradle依托：imgradle构建失利plementation group: ‘com.squareup.okhttp3’, name: ‘ookhttp封装khttp’, version: ‘3.14.9’

AsyncTimeout

AsyncTimeout类位于Okigithub永久回家地址o库，集成自Timeout。其类中有如下注释：

/*gitee*
* This timeout uses a background thread to take action exactly when the timeout occurs. Use this to
* implemgradlewent timeouts whegradle构建失利re they aren't supported natively, such as to sockets that are blocked on
* writing.
*
* <p>Subclasses should override {@link #timedOut} to takokhttp运用e action when a timeout occurs. This method
* will be invoked by the shared watchdog thregitlabad so it should notgithub中文官网网页 do any long-running opegradle下载慢解决办法rations.Git
* Otherwise we risk starappleving other timeouts from being triggered.
*
* <p>Use {@gradle是干什么的link #sink} and {@linkgradle下载慢解决办法 #source} to apply this tiapprovemeout to a stream.gradle装置装备 The returned value
* will apply theokhttp是干什么用的 timeout to each operation on the wrapped stream.
*
* <p>Callers should call {@link #entegradle是什么r} before doing work that is subject to timeouts, and {@link
* #exigit教程t} afterwards. The returgradlen value of {@link #exit} indicates wgradle是什么hgradleether a timeout was triggered.
* Note that thegithub call to {@link #timedOGitHubut} is asynchronous, and may be called after {@link #exit}.
*/
public class AsyncTimeout extends Timeout {

这儿供给了几个有用的信息：

• 这是一个运用共同子线程检测超时的东西gradle下载慢解决办法，首要针对的是一些原生不支持超时检测的类。
• 它供给了一个timedOut()办法，github中文社区作为检测到超时的回调。
• 内gradle构建失利部供给的sink()和sgithub永久回家地址ource()办法能够适配流的读写超时检测，这能够对应到网络央求的流读github永久回家地址写，后边会讲到。
• 供给enter()和egithub中文社区xit()作为初步计时和完毕计时的调用。也便是说初步实施计时的起点将会在enter()产生。

Timeout

上述一向在说超时检测，那究竟超时的时刻从何而来呢？先来看看Timeout中有如下界说：

  /**
* True if {@code deadlineNanoTime} is defined. There is no equivalent to null
* or 0 for {@link System#nanoTime}.
*/
private boolean hasDeadline;
private long deadlineNanoTime;
private long timeoutNanos;

Timeougithub下载t中界说了：deadlineNanoTigradle装置装备me也便okhttp3下载是dappointmenteadline时刻；timeoutNanos是超时时长。详细到其子类AsyncTimeout便是运用tiappreciatemeoutNanos来核算超时的。

AsyncTimeout特征界说

再来看giti是什么牌子看AsapplicationyncTokhttp面试imeout的一些特征界说，

  private static final int TIMEOUT_WRITE_SIZE = 64 * 1024;
private static final long IDLE_TIMgithub中文官网网页EOUT_MILokhttp运用LIS = TimeUniokhttp面试t.SECOgithub直播渠道永久回家NDS.toMillis(60);
private static final long IDLE_TIMEOUT_NANOS = TimOKHttpeUnit.MILLISECONDS.toNanos(IDLE_TIMEOUT_MILLIS);
static @Nullable AsyncTimegradle装置装备out head;
private boolean inQueue;
private @Nullable AsyncTimeout next;
private long timeoutAt;

• timgithub下载eoutAt：记载超时的详细时刻，giti这个的核算是approve经过初步计时github中文官网网页的当时时刻+上述的timeoutNanos。
• 上述代码出现了一个head和nappstoreext的界说，前面在AsyncTimeout的注释中讲到，它会经过一个共同的子线okhttp长处程进行超时检测。而这个head和next的界说即一个链表的结构，用于将每个Asynokhttp面试cTimeout政策构成一个部队，便当每次超时检测触发时的遍历。这个会在后边讲到。
• inQueue：github永久回家地址即AsyncTimeout政策一旦加入到链表中，就会置为true。

AsyncTimeout在网络央求流程中的运用

先来看看Asygradle构建失利ncTimeout详细在网络央求流程中的运用。

• 在Transmitter中有一个自带的AsyncTimeout类型特征，它的超时时刻timeoutNanos会在Transmitter的结构办法中设置，设置的是OkHttpClient初始化时自界说的callTimeoutgradle构建失利。这儿的超时检测的是整个央求的总时刻。

  private final AsyncTimeout timeout = new AsyncTimeout() {
  @Overrigiteede protected void timedOut() {
  cancel()giti轮胎;
  }
  };
  。。。
  public Transmitter(OkHttpClgithub是干什么的ient clgithub怎样下载文件ient, Call call) {
  this.client = client;
  this.connectionPool = Internal.instance.realConnectigiteeonPool(client.connectionPool());
  this.call = call;
  this.eventListener = client.eventListenergithub敞开私库Factory().create(call);
  this.timeout.Gittimeout(client.callTimeoutMillis(), MILLISECONDS);
  }
  

  cokhttp运用过程allTimeOKHttpout：整个央求appear进程的超时时刻，一般不设置默以为0

• 在树立衔接时会调用到RealConnection.connectSocket()，树立衔接之后会创建两个Okio相关的Buffgithub中文社区eredgitlabSource和BufferedSink政策。

  // RealConnection.connectSockegiti轮胎t()
  // RealConnection.java 2github永久回家地址75行okhttp运用
  source = Okio.buffer(Okio.source(rawSocket));
  sinkgithub打不开 = Okio.buffergradle构建失利(Okio.sink(rawSocket));
  // Okio.javagithub中文官网网页 22github永久回家地址1行
  public static Source source(Socket socket) thgiteerows IOEgithub是干什么的xception {
  if (applesocket == null) throw new IllegalArgumentException("socket == null");
  if (socket.getInputStream() == null) throw new IOException("githubsocket's input streamappstore == null");
  AsyncTimegithub中文官网网页out timeout = timeouapplicationt(socket);
  Source source = source(socket.getInputStream(), timeout);
  return timeout.source(source);
  }
  // Okio.java 115行
  public static Sigiti是什么牌子nk sink(Socket socket) throwOKHttps IOExcepokhttp3源码剖析tion {
  if (socket == null) thrAPPow new IllegalArgumentException("sockokhttp运用过程et == null");
  if (socket.getOutputStream() == null) throw new IOExcgithub中文官网网页eption("soappearcket's output stream == null");
  AsyncTimeout timeout = timeout(sogradle构建失利cket);
  Sink sink = sink(socgithub中文官网网页ket.getOutputStream(), timegradle怎样读out)giti;
  return timeout.sink(sink);
  }
  // RealCongradle下载慢解决办法nection.jagitlabva 542行
  ExchangeCodec newCodec(OkHttpCliokhttp运用过程ent client, Interceptor.ChGitHubagradle和maven的差异in chain) throws SocketException {
  if (http2gitiConnection != null) {
  return new Http2Exchgradle教程angeCodec(client, thisOKHttp, cappstorehain, http2Connection);
  } else {
  socket.setSoTimeout(chain.readTimeoutMillis(github中文官网网页));
  source.timegiteeout().timeout(chain.rgit命令eadTimeoutMillisokhttp源码解析(), MILLISECONokhttp面试DS);
  sink.timeout().timeout(chain.writAPPeTiGitmeoutMillis(), MILLISECONDS);
  return new Http1ExchangeCodec(clienokhttp面试答复t, thisgradle构建失利, source, sink);
  }
  }
  

  新建BufferedSource和BufferedSink政策时都需求先新建一个AsyncTgithub永久回家地址imeout，在GitHub运用其新建BufferedSource和BufferedSOKHttpink，这appstore儿的代码运用到了装修器的思维，继而将source和sink具有timeout的才干。后续在新建ExchangeCodec时，会别离设置OkHttpClient初始化时自界说的readTimeout和writeTimeout，对github直播渠道永久回家应读写的超时。

  readTimeout：读超时时刻，默许10s。

  writeTimeout：写gitee超时时刻，默许10s。

ps：因app装置下载为socket自身具有衔接超时的检测，故connectTimeout不需求选用AsyncTgithub中文官网网页imeout的计划。

AsyncTimGiteout超时检测

加入部队，初步检测

  // AsyncTimapproacheout.java 72行
public final void engradle和maven的差异ter() {
if (inQueue) tapproachhrow new IllegalStateExceptokhttp是干什么用的ion("Unbalanced enter/exit");
long timeoutNanos = timeoutNanos();application
boolean hasDeadline = hasDeadline();
if (timeoutNanos == 0 && !hasDeadline) {
return; // No timeout and no deadline? Don't bother wapproachith the queue.
}
inQueue = true;
scheduleTokhttp是干什么用的imeout(this, timeoutNanos, hasDeadline);
}

AsyncTimeout.enter()办法如上所示，调用之后正式进入超时检测。要点重视毕竟的scheduleTimeout(this, timeoutNanos, hasDeadline);这时一个static办法，还记得上面说到的AsyncTimeout有一个静态成员变量head吗？接下来就来看看这个办法。

  // AsyncTimeout.java 83行
private static syncokhttp3源码剖析hronized void scheduleTimeout(
AsyncTimeout node, long timeoutNanos, boolean hasapproachDeadline) {
// Start the watchdappearoggithub怎样下载文件 thread and create the headapple node whengradle和maven的差异 the first tigradle构建失利megithub官网out is schedulegithub官网d.
if (head == null) {
head = new AsyncTimeogithub中文官网网页ut();
new Watchdog().startokhttp面试答复();
}
long now = Systappearanceem.naapplenoTime();
if (timgithub打不开eoutNanos != 0 && hasDeadline) {
// Compute tapprovehe earlokhttp3下载iest event; either timeout or deadline. Because nanoTime can wrap around,
// Math.mingithub中文社区() is undefined for absolute values, but meaningful for relative ones.
node.tGitHubimeoutAt = now + Math.min(timeoutNangitlabos, node.deadlineNanookhttp源码解析Time() - now);
} else if (timeoutNanos != 0) {
node.timeoutAt = now + timeoutNanos;approach
} else if (hasDeadline) {
node.timeoutAt = node.deadlineNanoTime();
} else {
throw ngradlewew AssertionError();
}
// Insert the node in sorted order.
long remainingNanos = node.remainingNanos(now);
for (AsyncTimeout prev = head; true; prev = prev.next) {
if (prev.next == null || remainingNanosokhttp运用 < prev.next.remainingNanos(now)) {
node.next = prev.next;
prev.next = node;
if (prev == head) {
AsyncTimeout.class.notify(); // Wake up the watapprovechdog when inserting at the front.
}
break;
}
}
}

ps：node.github是干什么的remainingNanos(now);会计算出当时时刻与超时时刻的时刻距离。

办法中首要做了3件事：

• 静态变量head若为空，则说明大局检测还未打开，需求打开检测线程Watchdog。ps：head实际上仅仅一个部队初okhttp是干什么用的步的标志，自身不属于一次超时的检测。
• 核算出加入到检测部队的当时节点的超时时刻timeoutAt
• 将大局的检github永久回家地址测部队进行重排序，按照timeoutAt从小到大排序apple。保证后续Watchdog的检测机制。由所以链表结构，只需求将下一个节点改变指向即可。详细的次序可见下图（先用旅程图替代，当作时刻轴了解即可）：

journey
title AsyncTimeout部队次序（单位/ns）
now: 0
timeoutAt: 0
timeoutAt2: 0

Watchdog

Watchdog是整个AsyncTimeout超时检测机制的检测线程。

prappearanceivate static final class Watchdog extends Thread {
Watchdog() {gradle教程
super("Okio Watchdog");
setDaemon(true);
}
public void run() {
while (true) {
try {
AsyncTimeout timedOut;
synchronized (AsyncTimeout.class) {
timedOut = awgitiaitTimeout();
// Didn't finapp装置下载d a node to interrupt. Try again.
if (timappleedOut == null) continuegithub直播渠道永久回家;
// The queue is completely emptygithub. Let this thread exit and let anookhttp3源码剖析ther watchdog thread
// get created on the nexapprovet call to scheduleTimeout().
if (timedOut == head) {
head = null;
return;
}
}
// Close the timed out node.
timedOut.timedOut();
} catch (InterruptedException ignored) {
}
}
}
}

• 经过awaitTimeout()寻找出已超时的AsyncTimeout政策。
• 若timedOut政策为空，则持续检测。
• 若timedOut为head，说明链github打不开表中已无GitHub检测政策。可状况链表。
• 若timedOut为有用的已超时政策，则调用其timedOut()办法回调给注册监听方。
• 值得一提的是，在WatchDog的结构办法中设置了setappreciateDaemon(true);标明它是一个照顾进程。关于照顾进程能够看看setDagradlewemon详解。这gradle是什么样做的长处是，它能够依托打开它的线程封闭而封闭。
• 由于WatchDog是检测性质的线程，所以timedOut()办法内不该进行耗时操作gradlew，避免影响后续检测okhttp面试的进行。

awaitTimeout()github直播渠道永久回家

在Watchdog线程中经过调用awaitTimeout()找出现已过期的AsyncTimeout。

static @Nullable AsyncTimeout awaitTimeout() throws InterruptedException {gradlew
// Gegradle构建失利t the next eligible nodegithub中文官网网页.
AsyncTimeout node = head.next;
// The queue is empty. Wait until either somethingapproach is enqueued or the idle timeout elapses.
if (node == napplicationull) {
long startNanogradle装置装备s = System.nanoTime();
AsyncTimeout.class.wait(IDLE_TIMEOUT_MILLIS);
return heaapproachd.ngitiexgithub敞开私库t ==gradle是干什么的 null && (System.nanoTime() - startNanos) >= IDLE_TIMEOUT_NANOS
? head  // Thgithub下载e idle timeout elapsed.
: null; // The situation has chagithub中文官网网页nged.
}
long waitNanos = node.remainingNangithubos(Sgithub永久回家地址ystem.nanoTime());
// The head of the queue hasn't timed out yet. Await that.
iokhttp是干什么用的f (waitNanos > 0) {
// Waitinggit命令 is made complicated by the fact tgradle是什么hat we worgradle是干什么的k in nanoseconds,
// but the AgiteePI wants (millis, nanos) in two arguments.
long waitMillis =appointment waitNanos / 1000000L;
wappleaitNanos -= (waitMillis * 1000000L);
AsyncTimeout.claapp装置下载ss.wait(waitMillis, (int) waitNanos);
return null;
}
// The head of the queue has tigithub中文官网网页med out. Remove it.
happroachead.next = node.next;
node.next = null;
return node;
}

从代码可知，awaitTimeout()只会检测head.next。

• 若head.next为null，会先进approach入60s超时等候状况。okhttp长处
  • 若仍是没有就会以为超时检测部队现gradle已清空，Watchdog线程就会完okhttp长处毕。等下一次有新的检测时才会打开。
  • 若存在就会回来null，外部进行下一次循环。
• 若head.next的超时时刻比当时时刻早，就会进入以当时时刻与超时时刻的时刻差的超时等候状况。唤醒会也是回来null，外部进行下一次循环。
• awaitTimeout()运用了java多线程的wait()、notify/notifyAll() 机制。上述的scheduleTimeout(this, timeoutNanos, hasDeadline);办法在新node刺进链表后会调用AsyncTimeout.class.noapplicationtify();。这样做的目的是为了在没有超时的状况下让出资源。

Java多线程学习之waitgiti、notify/notifyAll 详解

退出检测

当流程走完时需求调用exit()将其okhttp3下载绑定的AsyncTimeoutappear政策移出链表。假如链表内找不到，则说明现已超时了…

  /** Returns true if the timeoutokhttp长处 occurred. *git教程/
public final boolean exit() {
if (!inQueue) return false;
inQueue = false;
return cancelScheduledTimeout(this);
}
/** Returns trokhttp源码解析ue if the timeout occurrgiteeed. */
private static synchronized boolean cancelScheduledTimeout(Asyncgithub敞开私库Timeout node) {
// Reokhttp运用move the node from the linked list.
for (AsyncTimeout prev = head; prev != null; prev = prev.next) {
ifgiti (prev.next == node) {
prev.next = node.next;
node.next = null;
return false;
}
}
// The node wasn't found in the linked list: it must have timed out!
return true;
}