115 lines
4.8 KiB
C#
115 lines
4.8 KiB
C#
//------------------------------------------------------------------------------
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// <copyright file="BackgroundWorkScheduler.cs" company="Microsoft">
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// Copyright (c) Microsoft Corporation. All rights reserved.
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// </copyright>
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//------------------------------------------------------------------------------
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namespace System.Web.Hosting {
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using System;
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using System.Threading;
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using System.Threading.Tasks;
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using System.Web.Util;
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internal sealed class BackgroundWorkScheduler : IRegisteredObject {
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private readonly CancellationTokenHelper _cancellationTokenHelper = new CancellationTokenHelper(canceled: false);
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private int _numExecutingWorkItems; // number of executing work items, not scheduled work items; a work item might never be scheduled
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private readonly Action<BackgroundWorkScheduler> _unregisterCallback;
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private readonly Action<AppDomain, Exception> _logCallback;
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private readonly Action _workItemCompleteCallback;
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internal BackgroundWorkScheduler(Action<BackgroundWorkScheduler> unregisterCallback, Action<AppDomain, Exception> logCallback, Action workItemCompleteCallback = null) {
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Debug.Assert(unregisterCallback != null);
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_unregisterCallback = unregisterCallback;
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_logCallback = logCallback;
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_workItemCompleteCallback = workItemCompleteCallback;
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}
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private void FinalShutdown() {
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_unregisterCallback(this);
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}
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// we can use 'async void' here since we're guaranteed to be off the AspNetSynchronizationContext
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private async void RunWorkItemImpl(Func<CancellationToken, Task> workItem) {
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Task returnedTask = null;
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try {
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returnedTask = workItem(_cancellationTokenHelper.Token);
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await returnedTask.ConfigureAwait(continueOnCapturedContext: false);
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}
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catch (Exception ex) {
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// ---- exceptions caused by the returned task being canceled
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if (returnedTask != null && returnedTask.IsCanceled) {
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return;
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}
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// ---- exceptions caused by CancellationToken.ThrowIfCancellationRequested()
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OperationCanceledException operationCanceledException = ex as OperationCanceledException;
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if (operationCanceledException != null && operationCanceledException.CancellationToken == _cancellationTokenHelper.Token) {
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return;
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}
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_logCallback(AppDomain.CurrentDomain, ex); // method shouldn't throw
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}
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finally {
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WorkItemComplete();
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}
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}
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public void ScheduleWorkItem(Func<CancellationToken, Task> workItem) {
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Debug.Assert(workItem != null);
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if (_cancellationTokenHelper.IsCancellationRequested) {
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return; // we're not going to run this work item
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}
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// Unsafe* since we want to get rid of Principal and other constructs specific to the current ExecutionContext
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ThreadPool.UnsafeQueueUserWorkItem(state => {
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lock (this) {
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if (_cancellationTokenHelper.IsCancellationRequested) {
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return; // we're not going to run this work item
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}
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else {
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_numExecutingWorkItems++;
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}
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}
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RunWorkItemImpl((Func<CancellationToken, Task>)state);
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}, workItem);
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}
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public void Stop(bool immediate) {
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// Hold the lock for as little time as possible
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int currentWorkItemCount;
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lock (this) {
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_cancellationTokenHelper.Cancel(); // dispatched onto a new thread
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currentWorkItemCount = _numExecutingWorkItems;
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}
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if (currentWorkItemCount == 0) {
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// There was no scheduled work, so we're done
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FinalShutdown();
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}
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}
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private void WorkItemComplete() {
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// Hold the lock for as little time as possible
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int newWorkItemCount;
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bool isCancellationRequested;
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lock (this) {
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newWorkItemCount = --_numExecutingWorkItems;
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isCancellationRequested = _cancellationTokenHelper.IsCancellationRequested;
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}
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// for debugging & unit tests
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if (_workItemCompleteCallback != null) {
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_workItemCompleteCallback();
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}
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if (newWorkItemCount == 0 && isCancellationRequested) {
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// Cancellation was requested, and we were the last work item to complete, so everybody is finished
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FinalShutdown();
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}
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}
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}
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}
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