I have written a program in c# for quick sort using multithreading. but the code has a problem. the array is not sorted properly. i think it is because the parent thread terminates soon before the child threads sort the array. i am attaching the code herewith. kindly help me.any help is highly appreciated. thanks in advance.

Beulah

using System; 
using System.Threading; 
using System.Collections; 

namespace QSort 
{ 
/// <summary> 
/// Summary description for Class1. 
/// </summary> 
class Class1 
{ 
/// <summary> 
/// The main entry point for the application. 
/// </summary> 
[STAThread] 
static void Main(string[] args) 
{ 
Class1 class1 = new Class1(); 
} 


//public int[] a = new int[10000000]; 
//added 
private const int MAX=6; 
public int[] a = new int[MAX]; 


public Class1() 
{ int choice=1; 
while (choice<3) 
{ 
Random random = new Random(); 
/*for(Int32 i=0;i<10000000;++i) 
a[i] = random.Next(100000000);*/ 
//added 
a[0]=20; 
a[1]=10; 
a[2]=40; 
a[3]=30; 
a[4]=60; 
a[5]=50; 
//}added 
ArrayList list = new ArrayList(); 
list.Add(0); 
list.Add(a.Length-1); 

DateTime startTime = DateTime.Now; 
Console.Write("1. SigleThreaded Sort\n2.MultithreadSort\nEnter Choice : "); 
choice=Convert.ToInt32(Console.ReadLine()); 
switch(choice) 
{ 
case 1: 
startTime = DateTime.Now; 
QSort(0, a.Length-1); 
break; 

case 2: 
//multithreading startTime = DateTime.Now; 
QSort(list); 
break; 
default: 
break; 
} 
if (choice<3) 
{ 
Console.WriteLine("Time Taken to sort "+a.Length.ToString() +" elements = "+(DateTime.Now.Subtract(startTime)).TotalMilliseconds.ToString()+" MilliSeconds"); 
//added 
for (int index=0; index<MAX; index++) 
Console.WriteLine(a[index]); 
} 

} 
} 



//this works fine 
public void QSort( int left, int right )//singlethreaded 
{ 
int pivot, lhold, rhold; 

lhold = left; 
rhold = right; 
pivot = a[left]; 

while( left < right ) 
{ 
while( (a[right] >= pivot) && (left < right) ) 
{ 
right--; 
} 

if( left != right ) 
{ 
a[left] = a[right]; 
left++; 
} 

while( (a[left] <= pivot) && (left < right) ) 
{ 
left++; 
} 

if( left != right ) 
{ 
a[right] = a[left]; 
right--; 
} 
} 

a[left] = pivot; 
pivot = left; 
left = lhold; 
right = rhold; 

if( left < pivot ) 
{ 
QSort( left, pivot-1 ); 
} 

if( right > pivot ) 
{ 
QSort( pivot+1, right ); 
} 
} 


//i have problem in this method 
public void QSort(object listObject) //Multithreaded 

{ 
Int32 left = (Int32)((ArrayList)listObject)[0]; 
Int32 right = (Int32)((ArrayList)listObject)[1]; 
int pivot, lhold, rhold; 

lhold = left; 
rhold = right; 
pivot = a[left]; 
lock(a) 
{ 
while( left < right ) 
{ 

while( (a[right] >= pivot) && (left < right) ) 
{ 
right--; 
} 

if( left != right ) 
{ 
a[left] = a[right]; 
left++; 
} 

while( (a[left] <= pivot) && (left < right) ) 
{ 
left++; 
} 

if( left != right ) 
{ 
a[right] = a[left]; 
right--; 
} 
} 

a[left] = pivot; 
pivot = left; 
left = lhold; 
right = rhold; 
} 

if( left < pivot ) 
{ 
ArrayList list = new ArrayList(); 
list.Add(left); 
list.Add(pivot-1); 
ThreadPool.QueueUserWorkItem(new WaitCallback(QSort),list); 
} 

if( right > pivot ) 
{ 
ArrayList list = new ArrayList(); 

list.Add(pivot+1); 
list.Add(right); 
ThreadPool.QueueUserWorkItem(new WaitCallback(QSort),list); 
} 
} 
} 
}

Recommended Answers

All 3 Replies

I by no means am an expert in threading but here is what i can gather from this.
you are using 'ThreadPool.QueueUserWorkItem' which queues the item into the current main thread.
What you need to do is create a whole new thread which i did not see.
which is something like:

myThread = new System.Threading.Thread(new 
   System.Threading.ThreadStart(myStartingMethod));
myThread.Start();

that creates a seperate thread from the main with a method to initialze it.
the locks go in functions that are shared by more then one thread, which could be a single function to change data in the array then a seperate function for sorting.

thank u for ur reply. but my code also allots a separte thread from the thread pool. the prob is how to prevent the main thread from terminating b4 the child thread terminates.

Beulah

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