Clarification on thread pool max threads

Question

I've read here that :

In v2.0, 3.5, and 4.0, ASP.NET initializes the CLR ThreadPool with 100 threads per processor(core)

That is correct , I checked it (I have 8 core machine , so 8*100 = 800):

But then I saw this and this:

maxWorkerThreads — Configures the maximum number of worker threads to use for the process on a per-CPU basis.The range for this attribute is from 5 through 100. The default is 20.

Question

I don't see how the numbers fits in here :

The first paragraph states that I have max 100 threads per core ( the image prove it , I have 8 cores).

But the second paragraph states that the default maximum worker threads per core is 20. So if I have 8 cores then I must have 8*20 = 160 max threads. not 800.

Can someone please shed light?

Update:

I just found a way to get the key element value via c# code :

So now the number are fit in ,but still - MSDN say the default is 20 , not 100

And then they do mention 100 :

What is going on here?

Solution

I have looked at source code and have found that default value for MaxWorkerThreads is set to 100

private static readonly ConfigurationProperty _propMaxWorkerThreads = new ConfigurationProperty("maxWorkerThreads", typeof (int), (object) 100, (TypeConverter) null, (ConfigurationValidatorBase) new IntegerValidator(1, 2147483646), ConfigurationPropertyOptions.None);

This field is added to properties collection in static constructor

ProcessModelSection._properties.Add(ProcessModelSection._propMaxWorkerThreads);

In property definition they do set default value to 20

[IntegerValidator(MaxValue = 2147483646, MinValue = 1)]
[ConfigurationProperty("maxWorkerThreads", DefaultValue = 20)]
public int MaxWorkerThreads

But this obviously give no effect. Maybe it's some kind of legacy implementation. By the way it behaves this way only if autoConfig is set to false. When it's set to true I have 32K worker threads in my application. Probably this behavior depends on IIS version.

Comments

[hackp0int]

@HenkHolterman Can you explain it further more with a deeper explanations.

[Royi Namir]

please read it again. request != thread. asp.net sets 100 threads per core. this attribute is for async operations

[cjcurrie]

@RoyiNamir, perhaps I misunderstand. .NET 4 in IIS 7 has 5000 max concurrent application pool threads per CPU, as reported on this page of the MSDN

[Royi Namir]

5000 max concurrent requsts ! not threads ! Again , thread != request. this is for async operations where a request doesnt tie a thread. (The difference only matters when the requests are asynchronous (the request either has an asynchronous handler or a module in the pipeline completes asynchronously). read this excat line here blogs.msdn.com/b/tmarq/archive/2007/07/21/…

[Royi Namir]

So the docs are old updated via attribute and not via property ?

[Andrii Litvinov]

Could be, I actually have no idea.

[Royi Namir]

p.s this whole uqestion came from this book chapter which I read i'll be glad if you have a look at the test he did there - which I don't understand : if each core has 100 threads to work , why does in the first 10 seconds - there were only 13 threads used ? why not more ? ( he did there synchronous operation which tie a thread)

[Royi Namir]

(continue)... but still - he says that threadpool create 2 more threads each second. but why create threads if asp.net already have 100 threads READY TO GO !!!! ? can u have alook at it ?

[Andrii Litvinov]

Actually ASP.NET doesn't have 100 threads at start time. ThreadPood creates new threads when requested up to minWorkerThreads value. Then if there are still work to do and threads are not enough it will add new thread each half a second when needed.

[Royi Namir]

no. asp.net does have 100 threads per core at start time. i.stack.imgur.com/RvJQ3.jpg ( this guy build iis core)

[Andrii Litvinov]

Try to check yourself by calling ThreadPool.GetMaxThreads and ThreadPool.GetAvailableThreads at application start time or when request is executed.

[Royi Namir]

My friend , I already have. ive been working on it for the last 5 days. look here and see how initializations threads are diffrent and how asp.net does set 100 threads per core i.stack.imgur.com/vbQhD.jpg

[Andrii Litvinov]

ThreadPool.GetMaxThreads doesn't give you number of threads created in thread pool. It's a number of threads that it is possible to create. Try check you app memory footprint. Each allocated thread takes about 1MB in memory. I don't think you app consumes 1GB at start time.

[Royi Namir]

if so , if i have 200 users who requests data from the server , they will wait a long time till threadpool will have enough threads( assuming prv threads still working)....

[Andrii Litvinov]

Exactly. You can set minWorkerThread to 25 for your 8 cores server if you know for sure that it will use it. But it is not recommended because if the load will fall down thread will still be in use but not that effective. Try read this article too.

[Royi Namir]

Thank you my friend. my mistake was missing the "max" word. I thout they are initially initialized to 100 threads. appraently they initialized to MAX 100 ( per core). however i still wonder how iis (8 core) takes care of many many simultainously requests ( ~2 sec each) while growing its thread pool threads by 2 per second.....

[Andrii Litvinov]

Sure, I send good time digging IIS and understanding how it works. I think for that many requests IIS maintains other queue. AFAIR this was described in those two articles from Thomas Marquardt. (One you've mentioned in you question).