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How to pass data to worker threads

, 30 Oct 2001 CPOL
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Shows how you can pass data to your worker threads

Introduction

There are some things about the .NET threading classes that I have not appreciated much. The first shock I got was when I realized that the System::Threading::Thread class was a sealed class.

public __gc __sealed class Thread

That means we cannot derive from the Thread class. If Thread was not sealed, then things would have been really easy. We derive a class from Thread, say MyThread. Then we add a struct member to MyThread so that we can populate our struct before starting the thread. This would have been a clean way to pass data to our thread.

As if that was not bad enough, my next shock was when I realized that the thread proc delegate would not take any parameters.

public __gc __delegate void ThreadStart();

The API function CreateThread has an LPVOID paramater using which we can pass a struct or class pointer to pass data to our threads. The CRT functions _beginthread and  _beginthreadex have a void* argument which we can use similarly.

Well so how do we get around these drawbacks. I presume that there are some very valid reasons for the Thread class and the ThreadStart delegate having the above mentioned definitions. And if someone knows why they are so, I'd be glad if you can enlighten me.

I might have missed out on something. Two likely candidates are AllocateDataSlot and AllocateNamedDataSlot. I haven't really understood their exact purpose. But I guess I'll have to search deeper into the documentation.

Anyway for now I have found the following solutions. We have our own managed class. And we add a Thread member to our class. And  in our constructor we start our thread using the Thread member. I am not sure whether this is an ideal solution. The following program listing will try and make things clear.

Program Listing

#include "stdafx.h"

#using <mscorlib.dll>

using namespace System;
using namespace System::Threading;

__gc class CalcThread
{
public:
    CalcThread(int num,String *s);
private:
    void ThreadFunc();
    Thread *t;
    int x;
    String *s1;
};

int wmain(void)
{   
    CalcThread *c1,*c2,*c3;
    Console::WriteLine("Starting thread c1");
    c1=new CalcThread(77,"c1");
    Console::WriteLine("Starting thread c2");
    c2=new CalcThread(66,"c2");
    Console::WriteLine("Starting thread c3");
    c3=new CalcThread(99,"c3");
    return 0;
}

CalcThread::CalcThread(int num, String *s)
{
    x=num;
    s1=s;
    t=new Thread(new ThreadStart(this,&CalcThread::ThreadFunc));	
    t->Start();
}

void CalcThread::ThreadFunc()
{
    Console::WriteLine("Thread {0} has initialized",s1);
    for(int i=0;i<5;i++)
    {		
        x^=i;
        Console::WriteLine("Thread {0} Intermediate Result : {1}",
            s1,__box(x));
        Thread::Sleep(500);
    }
    Console::WriteLine("Thread {0} finished with result {1}",
        s1,__box(x));
}

Output

D:\MyProjs\mcppthreads01\Debug>mcppthreads01.exe
Starting thread c1
Starting thread c2
Starting thread c3
Thread c1 has initialized
Thread c1 Intermediate Result : 77
Thread c2 has initialized
Thread c2 Intermediate Result : 66
Thread c3 has initialized
Thread c3 Intermediate Result : 99
Thread c1 Intermediate Result : 76
Thread c2 Intermediate Result : 67
Thread c3 Intermediate Result : 98
Thread c1 Intermediate Result : 78
Thread c2 Intermediate Result : 65
Thread c3 Intermediate Result : 96
Thread c1 Intermediate Result : 77
Thread c2 Intermediate Result : 66
Thread c3 Intermediate Result : 99
Thread c1 Intermediate Result : 73
Thread c2 Intermediate Result : 70
Thread c3 Intermediate Result : 103
Thread c1 finished with result 73
Thread c2 finished with result 70
Thread c3 finished with result 103

D:\MyProjs\mcppthreads01\Debug>

Thank You

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Nish Sivakumar

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
 
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - www.voidnish.com where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff - blog.voidnish.com.
 
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
 
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
 
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

 
AnswerSystem::Threading::Thread class is a sealed class Pinmemberhariseos20-May-12 23:27 
GeneralThread waiting PinsussOleshii20-Jan-04 0:47 
QuestionPassing Data? PinmemberWilliam E. Kempf31-Oct-01 12:21 
AnswerRe: Passing Data? PinmemberNish [BusterBoy]31-Oct-01 13:08 
GeneralDeriving from Thread class PinmemberDaniel Turini30-Oct-01 23:36 
GeneralRe: Deriving from Thread class PinmemberNish [BusterBoy]30-Oct-01 23:50 
GeneralRe: Deriving from Thread class PinmemberDaniel Turini31-Oct-01 0:16 
GeneralRe: Deriving from Thread class PinmemberNish [BusterBoy]31-Oct-01 0:40 
GeneralRe: Deriving from Thread class PinmemberJörgen Sigvardsson30-Oct-01 23:51 
GeneralRe: Deriving from Thread class PinmemberNish [BusterBoy]31-Oct-01 0:42 
GeneralRe: Deriving from Thread class PinmemberJörgen Sigvardsson31-Oct-01 1:10 
GeneralRe: Deriving from Thread class PinmemberNish [BusterBoy]31-Oct-01 6:24 
GeneralRe: Deriving from Thread class Pinmemberreader31-Oct-01 9:05 
What your strong?
GeneralRe: Deriving from Thread class PinmemberNish [BusterBoy]31-Oct-01 13:08 
GeneralThis time... PinmemberNish [BusterBoy]30-Oct-01 20:49 

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