Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / xsp / System / Web / UI / PageAsyncTaskManager.cs / 5 / PageAsyncTaskManager.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //----------------------------------------------------------------------------- namespace System.Web.UI { using System; using System.Collections; using System.Security; using System.Security.Permissions; using System.Threading; using System.Web; using System.Web.UI; using System.Web.Util; internal class PageAsyncTaskManager { private Page _page; private HttpApplication _app; private HttpAsyncResult _asyncResult; private bool _failedToStart; private ArrayList _tasks; private DateTime _timeoutEnd; private volatile bool _timeoutEndReached; private volatile bool _inProgress; private int _tasksStarted; private int _tasksCompleted; private WaitCallback _resumeTasksCallback; private Timer _timeoutTimer; internal PageAsyncTaskManager(Page page) { _page = page; _app = page.Context.ApplicationInstance; _tasks = new ArrayList(); _resumeTasksCallback = new WaitCallback(this.ResumeTasksThreadpoolThread); } internal HttpApplication Application { get { return _app; } } internal void AddTask(PageAsyncTask task) { _tasks.Add(task); } internal bool AnyTasksRemain { get { for (int i = 0; i < _tasks.Count; i++) { PageAsyncTask task = (PageAsyncTask)_tasks[i]; if (!task.Started) { return true; } } return false; } } internal bool FailedToStartTasks { get { return _failedToStart; } } internal bool TaskExecutionInProgress { get { return _inProgress; } } private Exception AnyTaskError { get { for (int i = 0; i < _tasks.Count; i++) { PageAsyncTask task = (PageAsyncTask)_tasks[i]; if (task.Error != null) { return task.Error; } } return null; } } private bool TimeoutEndReached { get { if (!_timeoutEndReached && (DateTime.UtcNow >= _timeoutEnd)) { _timeoutEndReached = true; } return _timeoutEndReached; } } private void WaitForAllStartedTasks(bool syncCaller, bool forceTimeout) { // don't foreach because the ArrayList could be modified by tasks' end methods for (int i = 0; i < _tasks.Count; i++) { PageAsyncTask task = (PageAsyncTask)_tasks[i]; if (!task.Started || task.Completed) { continue; } // need to wait, but no longer than timeout. if (!forceTimeout && !TimeoutEndReached) { DateTime utcNow = DateTime.UtcNow; if (utcNow < _timeoutEnd) { // re-check not to wait negative time span WaitHandle waitHandle = task.AsyncResult.AsyncWaitHandle; if (waitHandle != null) { bool signaled = waitHandle.WaitOne(_timeoutEnd - utcNow, false); if (signaled && task.Completed) { // a task could complete before timeout expires // in this case go to the next task continue; } } } } // start polling after timeout reached (or if there is no handle to wait on) bool taskTimeoutForced = false; while (!task.Completed) { if (forceTimeout || (!taskTimeoutForced && TimeoutEndReached)) { task.ForceTimeout(syncCaller); taskTimeoutForced = true; } else { Thread.Sleep(50); } } } } internal void RegisterHandlersForPagePreRenderCompleteAsync() { _page.AddOnPreRenderCompleteAsync( new BeginEventHandler(this.BeginExecuteAsyncTasks), new EndEventHandler(this.EndExecuteAsyncTasks)); } private IAsyncResult BeginExecuteAsyncTasks(object sender, EventArgs e, AsyncCallback cb, object extraData) { return ExecuteTasks(cb, extraData); } private void EndExecuteAsyncTasks(IAsyncResult ar) { _asyncResult.End(); } internal HttpAsyncResult ExecuteTasks(AsyncCallback callback, Object extraData) { _failedToStart = false; _timeoutEnd = DateTime.UtcNow + _page.AsyncTimeout; _timeoutEndReached = false; _tasksStarted = 0; _tasksCompleted = 0; _asyncResult = new HttpAsyncResult(callback, extraData); bool waitUntilDone = (callback == null); if (waitUntilDone) { // when requested to wait for tasks, before starting tasks // make sure that the lock can be suspended. try {} finally { try { Monitor.Exit(_app); Monitor.Enter(_app); } catch (SynchronizationLockException) { _failedToStart = true; throw new InvalidOperationException(SR.GetString(SR.Async_tasks_wrong_thread)); } } } _inProgress = true; try { // all work done here: ResumeTasks(waitUntilDone, true /*onCallerThread*/); } finally { if (waitUntilDone) { _inProgress = false; } } return _asyncResult; } private void ResumeTasks(bool waitUntilDone, bool onCallerThread) { #if DBG Debug.Trace("Async", "TaskManager.ResumeTasks: onCallerThread=" + onCallerThread + ", _tasksCompleted=" + _tasksCompleted + ", _tasksStarted=" + _tasksStarted); if (waitUntilDone) { // must be on caller thread to wait Debug.Assert(onCallerThread); } #endif // artifically increment the task count by one // to make sure _tasksCompleted doesn't become equal to _tasksStarted during this method Interlocked.Increment(ref _tasksStarted); try { if (onCallerThread) { ResumeTasksPossiblyUnderLock(waitUntilDone); } else { lock (_app) { HttpApplication.ThreadContext threadContext = null; try { threadContext = _app.OnThreadEnter(); ResumeTasksPossiblyUnderLock(waitUntilDone); } finally { if (threadContext != null) { threadContext.Leave(); } } } } } finally { // complete the bogus task introduced with incrementing _tasksStarted at the beginning TaskCompleted(onCallerThread); } } private void ResumeTasksPossiblyUnderLock(bool waitUntilDone) { while (AnyTasksRemain) { bool someTasksStarted = false; bool realAsyncTaskStarted = false; bool parallelTaskStarted = false; // start the tasks for (int i = 0; i < _tasks.Count; i++) { PageAsyncTask task = (PageAsyncTask)_tasks[i]; if (task.Started) { continue; // ignore already started tasks } if (parallelTaskStarted && !task.ExecuteInParallel) { // already started a parallel task, so need to ignore sequential ones continue; } someTasksStarted = true; Interlocked.Increment(ref _tasksStarted); task.Start(this, _page, EventArgs.Empty); if (task.CompletedSynchronously) { continue; // ignore the ones completed synchornously } // at this point a truly async task has been started realAsyncTaskStarted = true; if (task.ExecuteInParallel) { parallelTaskStarted = true; } else { // only one sequential task at a time break; } } if (!someTasksStarted) { // no tasks to start, all done break; } if (!TimeoutEndReached && realAsyncTaskStarted && !waitUntilDone) { // make sure we have a timer going StartTimerIfNeeeded(); // unwind the stack for async callers break; } // need to wait until tasks comlete, but the wait // must be outside of the lock (deadlock otherwise) // this code is always already under lock bool locked = true; try { // outer code has lock(_app) { ... } // the assumption here is that Monitor.Exit undoes the lock try {} finally { Monitor.Exit(_app); locked = false; } WaitForAllStartedTasks(true /*syncCaller*/, false /*forceTimeout*/); } finally { if (!locked) { Monitor.Enter(_app); } } } } private void ResumeTasksThreadpoolThread(Object data) { ResumeTasks(false /*waitUntilDone*/, false /*onCallerThread*/); } internal void TaskCompleted(bool onCallerThread) { int newTasksCompleted = Interlocked.Increment(ref _tasksCompleted); Debug.Trace("Async", "TaskManager.TaskCompleted: onCallerThread=" + onCallerThread + ", _tasksCompleted=" + newTasksCompleted + ", _tasksStarted=" + _tasksStarted); if (newTasksCompleted < _tasksStarted) { // need to wait for more completions return; } // check if any tasks remain not started if (!AnyTasksRemain) { // can complete the caller - all done _inProgress = false; _asyncResult.Complete(onCallerThread, null /*result*/, AnyTaskError); return; } // need to resume executing tasks if (Thread.CurrentThread.IsThreadPoolThread) { // if on thread pool thread, use the current thread ResumeTasks(false /*waitUntilDone*/, onCallerThread); } else { // if on a non-threadpool thread, requeue ThreadPool.QueueUserWorkItem(_resumeTasksCallback); } } private void StartTimerIfNeeeded() { if (_timeoutTimer != null) { return; } // calculate the wait time DateTime utcNow = DateTime.UtcNow; if (utcNow >= _timeoutEnd) { return; } double timerPeriod = (_timeoutEnd - utcNow).TotalMilliseconds; if (timerPeriod >= (double)Int32.MaxValue) { // timeout too big to launch timer (> ~25 days, plenty enough for an async page task) return; } // start the timer Debug.Trace("Async", "Starting timeout timer for " + timerPeriod + " ms"); _timeoutTimer = new Timer(new TimerCallback(this.TimeoutTimerCallback), null, (int)timerPeriod, -1); } internal void DisposeTimer() { Timer timer = _timeoutTimer; if (timer != null && Interlocked.CompareExchange(ref _timeoutTimer, null, timer) == timer) { timer.Dispose(); } } private void TimeoutTimerCallback(Object state) { DisposeTimer(); // timeout everything that's left WaitForAllStartedTasks(false /*syncCaller*/, false /*forceTimeout*/); } internal void CompleteAllTasksNow() { WaitForAllStartedTasks(true /*syncCaller*/, true /*forceTimeout*/); } } }
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