CODEWITHSUNDEEP
c#multithreading.net-2.0threadpool
techknowfreak
techknowfreak

Reputation: 279

Threadpool QueueUserWorkItem without using SetMaxThreads,GetMaxThreads

I'm using Threadpool to do some parallel processing in c# .NET 2.0.

Code :

int MAXThreads=GetConfigValue("MaxThreadLimit"); //This value is read from app.config

ManualResetEvent[] doneEvents=new ManualResetEvent[MAXThreads];
for(int i=0;i<MaxThreads,i++)
{

doneEvents[i]=new ManualResetEvent(false);

//create workload
DoProcess job=new DoProcess(workload,doneEvents[i]);
ThreadPool.QueueUserWorkItem(job.ThreadPoolCallBack,i);

}
WaitHandle.WaitAll(doneEvents);

//proceed

Class DoProcess
{
private WorkLoad load;
private ManualResetEvent doneEvent;
public DoProcess(WorkLoad load,ManualResetEvent doneEvent)
{
this.load=load;
this.doneEvent=doneEvent;
}
public void ThreadPoolCallBack(object index)
{
//Do Processing
doneEvent.Set();
}
}

MAXThreads value is being read from config but I guess this has nothing to do with the actual number of threads generated. Only few ~4-5 threads handle all the workload. I want thread count to be fixed somewhere around 20. How can I achieve this? Am I missing on something?..Does SetMaxThreads address this issue?..The above code will run on quad core cpu.

Upvotes: 1

Views: 1728

Answers (3)

Chris Gessler
Chris Gessler

Reputation: 23113

Assuming this is a C# application, you can use .NET Framework 4's Parallel programming model and limit the threads to 20.

Parallel.For(0, n, new ParallelOptions { MaxDegreeOfParallelism = 20 }, 
  i => 
  { 
    DoWork(i);
  });

However, if this is a web site/app, it's best to stay away from the ThreadPool all together, except for really small jobs, 1-2 threads, because you don't want to starve the ThreadPool. And NEVER set the max or min threads in the code, because it will affect your entire site, and all other sites using the same thread pool.

In this case, I recommend using SmartThreadPool instead.

Upvotes: 0

Hans Passant
Hans Passant

Reputation: 941655

You'd have to set the minimum number of threads instead.

That's not a very good idea in general, running more threads than you have processor cores usually gets less work done since the operating system is spending time swapping them in and out. These context switches are not cheap. The threadpool manager does its best to limit the number of active threads to the number of cores. Only allowing more threads to run when the existing ones don't complete in time. Up to the maximum number of threads. An enormous value by default, 1000 in your case.

Only increase the min threads when those worker threads are not performing enough work because they are blocked on I/O too often. In which case you really ought to consider Thread objects instead of thread pool threads.

Upvotes: 3

Tudor
Tudor

Reputation: 62439

There is also SetMinThreads in the ThreadPool class. Setting both min and max to the same value "should" fix the number of threads, but what actually happens under the hood is anybody's guess.

MSDN:

The thread pool provides new worker threads or I/O completion threads on demand until it reaches the minimum for each category.

So setting the minimum number of threads to 20 should give you no less than 20 threads in the pool.

Upvotes: 0

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