The Blog of Ian Mercer.

Task Parallel Library: A scheduler with priority, apartment state and maximum degree of parallelism

Here is an alternative scheduler for the Task Parallel Library. This one lets you set the maximum degree of concurrency, the apartment state and the thread priority for your work queue. To use it simply pass a new instance to the TaskFactory constructor and then schedule tasks on that TaskFactory.


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;
using System.Collections.Concurrent;
using System.Diagnostics;

namespace Utility
{
    ///
    /// TaskScheduler that uses the task parallel library, complete with all the new wonderful task cancellation features
/// This one adds the ability to set ApartmentState, ThreadPriority,
MaximumConcurrency and does some logging /// public class TaskScheduler2
: TaskScheduler, IDisposable { private ApartmentState apartmentState;
private ThreadPriority threadPriority;

private readonly List threads;

private BlockingCollection

tasks;

/// /// An MTA, BelowNormal TaskScheduler with the appropriate number of
threads /// public TaskScheduler2 (int numberOfThreads) :
this(numberOfThreads, ApartmentState.MTA, ThreadPriority.BelowNormal) {
}

public TaskScheduler2(int numberOfThreads, ApartmentState
apartmentState, ThreadPriority threadPriority) { this.apartmentState =
apartmentState; this.threadPriority = threadPriority;

if (numberOfThreads \< 1) throw new
ArgumentOutOfRangeException("numberOfThreads");

tasks = new BlockingCollection

();

threads = Enumerable.Range(0, numberOfThreads).Select(i =\> { var thread
= new Thread(() =\> { foreach (var task in
tasks.GetConsumingEnumerable()) { ExecuteTaskWithTiming(task, "queued");
} }); thread.IsBackground = true; thread.Priority = this.threadPriority;
thread.SetApartmentState(this.apartmentState); return thread;
}).ToList();

threads.ForEach(t =\> t.Start()); }

protected override void QueueTask(Task task) { tasks.Add(task); }

protected override IEnumerable

GetScheduledTasks() { return tasks.ToArray(); }

protected override bool TryExecuteTaskInline(Task task, bool
taskWasPreviouslyQueued) { // this is used to execute the Task on the
thread that is waiting for it - i.e. INLINE // it needs to check the
Apartment state and any other requirements if
(Thread.CurrentThread.GetApartmentState() != this.apartmentState) return
false; // can't execute on wrong Appt state if
(Thread.CurrentThread.Priority != this.threadPriority) return false; //
can't execute on wrong priority of thread either return
ExecuteTaskWithTiming(task, "inline"); }

private bool ExecuteTaskWithTiming(Task task, string contextInfo) {
Stopwatch sw = Stopwatch.StartNew(); Debug.WriteLine("Starting " +
contextInfo + " task"); bool ok = TryExecuteTask(task);
Debug.WriteLine("Ending " + contextInfo + " task, took " +
sw.ElapsedMilliseconds + "ms"); return ok; }

protected override bool TryDequeue(Task task) { return
base.TryDequeue(task); }

public override int MaximumConcurrencyLevel { get { return
threads.Count; } }

public void Dispose() { if (tasks != null) { tasks.CompleteAdding();

foreach (var thread in threads) thread.Join();

tasks.Dispose(); tasks = null; } } } } 

Related Stories

My love/hate relationship with Stackoverflow

Stackoverflow is a terrific source of information but can also be infuriating.

Ian Mercer
Ian Mercer

Xamarin Forms Application For Home Automation

Building a Xamarin Forms application to control my home automation system

Ian Mercer
Ian Mercer

JSON Patch - a C# implementation

Ian Mercer
Ian Mercer

Websites should stop using passwords for login!

A slightly radical idea to eliminate passwords from many of the websites you use just occasionally

Ian Mercer
Ian Mercer

Dynamically building 'Or' Expressions in LINQ

How to create a LINQ expression that logically ORs together a set of predicates

Ian Mercer
Ian Mercer

VariableWithHistory - making persistence invisible, making history visible

A novel approach to adding history to variables in a programming language

Ian Mercer
Ian Mercer

Neo4j Meetup in Seattle - some observations

Some observations from a meetup in Seattle on graph databases and Neo4j

Ian Mercer
Ian Mercer

Updated Release of the Abodit State Machine

A hierarchical state machine for .NET

Ian Mercer
Ian Mercer

My first programme [sic]

At the risk of looking seriously old, here's something found on a paper tape

Ian Mercer
Ian Mercer

Building a better .NET State Machine

A state machine for .NET that I've released on Nuget

Ian Mercer
Ian Mercer

The Internet of Dogs

Connecting our dog into the home automation

Ian Mercer
Ian Mercer

A simple state machine in C#

State machines are useful in many contexts but especially for home automation

Ian Mercer
Ian Mercer

Convert a property getter to a setter

Ian Mercer
Ian Mercer

MongoDB Map-Reduce - Hints and Tips

Ian Mercer
Ian Mercer

Weather Forecasting for Home Automation

Ian Mercer
Ian Mercer

Lengthening short Urls in C#

Ian Mercer
Ian Mercer

Why don't you trust your build system?

Ian Mercer
Ian Mercer

ASP.NET MVC SEO - Solution Part 1

Ian Mercer
Ian Mercer

Elliott 803 - An Early Computer

Ian Mercer
Ian Mercer

Building sitemap.xml for SEO ASP.NET MVC

Ian Mercer
Ian Mercer

Continuous Integration -> Continuous Deployment

What is "quality" in terms of a released software product or website?

Ian Mercer
Ian Mercer

Making a bootable Windows 7 USB Memory Stick

Here's how I made a bootable USB memory stick for Windows 7

Ian Mercer
Ian Mercer

Tip: getting the index in a foreeach statement

A tip on using LINQ's Select expression with an index

Ian Mercer
Ian Mercer

SQL Server - error: 18456, severity: 14, state: 38 - Incorrect Login

A rant about developers using the same message for different errors

Ian Mercer
Ian Mercer

WCF and the SYSTEM account

Namespace reservations and http.sys, my, oh my!

Ian Mercer
Ian Mercer

404 errors on IIS6 with ASP.NET 4 Beta 2

Ian Mercer
Ian Mercer

Mixed mode assembly errors after upgrade to .NET 4 Beta 2

Fixing this error was fairly simple

Ian Mercer
Ian Mercer

The EntityContainer name could not be determined

How to fix the exception "the entitycontainer" name could not be determined

Ian Mercer
Ian Mercer

Shortened URLs should be treated like a Codec ...

Expanding URLs would help users decide whether or not to click a link

Ian Mercer
Ian Mercer

Tagging File Systems

Isn't it time we stopped knowing which drive our file is on?

Ian Mercer
Ian Mercer

A great site for developing and testing regular expressions

Just a link to a site I found useful

Ian Mercer
Ian Mercer

Introducing Jigsaw menus

A novel UI for menus that combines a breadcrumb and a menu in one visual metaphor

Ian Mercer
Ian Mercer

Entity Framework in .NET 4

Ian Mercer
Ian Mercer

Fix for IE's overflow:hidden problem

Ian Mercer
Ian Mercer

A better Tail program for Windows

A comparison of tail programs for Windows

Ian Mercer
Ian Mercer

Measuring website browser performance

Found this great resource on website performance

Ian Mercer
Ian Mercer

Amazon Instance vs Dedicated Server comparison

Some benchmark performance for Amazon vs a dedicated server

Ian Mercer
Ian Mercer

System.Data.EntitySqlException

Hints for dealing with this exception

Ian Mercer
Ian Mercer

Agile Software Development is Like Sailing

You cannot tack too often when sailing or you get nowhere. Agile is a bit like that.

Ian Mercer
Ian Mercer

Exception Handling using Exception.Data

My latest article on CodeProject covers the lesser known Exception.Data property

Ian Mercer
Ian Mercer

Javascript error reporting

Sending client-side errors back to a server for analysis

Ian Mercer
Ian Mercer

AntiVirus Software is the Worst Software!

When your anti-virus software starts stealing your personal data, it's time to remove it!

Ian Mercer
Ian Mercer

ASP.NET Custom Validation

How to solve a problem encountered with custom validation in ASP.NET

Ian Mercer
Ian Mercer

Optimization Advice

Some advice on software optimization

Ian Mercer
Ian Mercer

Linq's missing link

LinqKit came in handy back in 2009

Ian Mercer
Ian Mercer

Google Chart API

Ian Mercer
Ian Mercer

Cache optimized scanning of pairwise combinations of values

Using space-filling curves to optimize caching

Ian Mercer
Ian Mercer

Threading and User Interfaces

A rant about how few software programs get threading right

Ian Mercer
Ian Mercer

Take out the trash!

Why Windows shutdown takes so long

Ian Mercer
Ian Mercer

Dell upgrades - a pricey way to go

Ian Mercer
Ian Mercer

Programming mostly C#

Ian's advice on programming

Ian Mercer
Ian Mercer