Orchard源码：热启动

概述

IIS线程池中的线程数量是有限制的。当有多个长时间请求时，可能会耗尽IIS可用线程。出现503错误。在MVC中。当遇到非CPU操作的长时间请求时，MVC提供了异步方法来解决这个问题。

例：利用async和await实现异步方法

// GET: Async

[AsyncTimeout(1000)]

public async Task<ActionResult> Index()

{

var data = await GetPageTaskAsync("http://www.baidu.com");

return data;

}

回到Orchard,在Orchard启动时,需要一定时间加载模块插件，这时候如果出现大量请求，则有可能出现上面提到的错误。来看一下Orchard中是如何解决这个问题。

项目结构Orchard.WarmupStarter ，是一个单独的项目。方便复用

具体实现

一句话概括实现步骤: 启动时初始化一个异步请求列表，初始化期间有请求到来时，把该请求添加到请求列表中。当系统初始化完成时回调起步请求列表并且清空。

Starter.cs

/// <summary>

/// Run the initialization delegate asynchronously in a queued work item

/// </summary>

public void LaunchStartupThread(HttpApplication application) {

// Make sure incoming requests are queued

WarmupHttpModule.SignalWarmupStart();

ThreadPool.QueueUserWorkItem(

state => {

try {

var result = _initialization(application);

_initializationResult = result;

}

catch (Exception e) {

lock (_synLock) {

_error = e;

_previousError = null;

}

}

finally {

// Execute pending requests as the initialization is over

WarmupHttpModule.SignalWarmupDone();

}

});

}

WarmupHttpModule.SignalWarmupStart(); 系统开始加载，初始化请求列表

public static void SignalWarmupStart() {

lock (_synLock) {

if (_awaiting == null) {

_awaiting = new List<Action>();

}

}

}

WarmupHttpModule.SignalWarmupDone(); 系统加载完成，回调请求列表并且清空

public static void SignalWarmupDone() {

IList<Action> temp;

lock (_synLock) {

temp = _awaiting;

_awaiting = null;

}

if (temp != null) {

foreach (var action in temp) {

action();

}

}

}

WebConfig中注册WarmupHttpModule

请求到来时，执行WarmupHttpModule.BeginBeginRequest回调, 如果加载中，则请求添加到异步列表，否则继续执行回调

private IAsyncResult BeginBeginRequest(object sender, EventArgs e, AsyncCallback cb, object extradata) {

// host is available, process every requests, or file is processed

if (!InWarmup() || WarmupUtility.DoBeginRequest(_context)) {

var asyncResult = new DoneAsyncResult(extradata);

cb(asyncResult);

return asyncResult;

}

else {

// this is the "on hold" execution path

var asyncResult = new WarmupAsyncResult(cb, extradata);

Await(asyncResult.Completed);

return asyncResult;

}

}

异步编程模型 DoneAsyncResult 和 WarmupAsyncResult 实现IAsyncResult

WarmupAsyncResult

/// <summary>

/// AsyncResult for "on hold" request (resumes when "Completed()" is called)

/// </summary>

private class WarmupAsyncResult : IAsyncResult {

private readonly EventWaitHandle _eventWaitHandle = new AutoResetEvent(false/*initialState*/);

private readonly AsyncCallback _cb;

private readonly object _asyncState;

private bool _isCompleted;

public WarmupAsyncResult(AsyncCallback cb, object asyncState) {

_cb = cb;

_asyncState = asyncState;

_isCompleted = false;

}

public void Completed() {

_isCompleted = true;

_eventWaitHandle.Set();

_cb(this);

}

bool IAsyncResult.CompletedSynchronously {

get { return false; }

}

bool IAsyncResult.IsCompleted {

get { return _isCompleted; }

}

object IAsyncResult.AsyncState {

get { return _asyncState; }

}

WaitHandle IAsyncResult.AsyncWaitHandle {

get { return _eventWaitHandle; }

}

}

DoneAsyncResult(不阻塞)

/// <summary>

/// Async result for "ok to process now" requests

/// </summary>

private class DoneAsyncResult : IAsyncResult {

private readonly object _asyncState;

private static readonly WaitHandle _waitHandle = new ManualResetEvent(true/*initialState*/);

public DoneAsyncResult(object asyncState) {

_asyncState = asyncState;

}

bool IAsyncResult.CompletedSynchronously {

get { return true; }

}

bool IAsyncResult.IsCompleted {

get { return true; }

}

WaitHandle IAsyncResult.AsyncWaitHandle {

get { return _waitHandle; }

}

object IAsyncResult.AsyncState {

get { return _asyncState; }

}

}

总结

Orchard.WarmupStarter 已封装好相关热启动代码， 实际项目中如果初始化时间比较长，稍改造Orchard.WarmupStarter就可复用到自己的项目中。

参考

http://www.cnblogs.com/alby/archive/2012/10/18/orchard-WarmupStarter.html