Question

I am starting atmost 5 threads in a program in C# .NET. But sometimes some of those threads just quit or become dead inexplicably even before the completion of execution of the function assigned to it.

It happens randomly . If I try to debug the code by putting breakpoints- It works fine.

And sometimes all the threads execute the assigned functions perfectly.They do not share any resources among them.

            Thread[] td = new Thread[5];             for (count = 4; count >= 0; --count)             {                 ds[count] = dba.getData(ru[count]);                 td[count] = new Thread(delegate() {  runRule[count].performTask(ru[count], ds[count], count); });                 td[count].Name = 'Thread ' + count.ToString();                 td[count].Start();                 Thread.Sleep(50);             } 

If I remove the last line ‘Thread.Sleep(50)’ only the first thread stared runs and rest of them just die.

can someone explain why the threads are becoming dead?

Answer 1

I suspect they’re not becoming dead – I suspect the problem is that you’re not actually running the rules you think you are. When you use a method’s local variables within an anonymous method, the variables themselves are captured. In this case, you’re capturing the count local variable – and then changing it (as the loop counter decreases). By the time a thread created when count=4 starts running, count may be 3 – so it will be calling runRule[3].performTask(ru[3], ds[3], 3). In fact, count could change while the expressions are being evaluated which could cause a lot of fun.

The way to get round this is to have a different ‘local’ variable for each iteration of the loop. It’s easy to do:

Thread[] td = new Thread[5]; for (count = 4; count >= 0; --count) {     int copy = count;     ds[count] = dba.getData(ru[count]);     td[count] = new Thread(delegate() {           runRule[copy].performTask(ru[copy], ds[copy], copy);      });     td[count].Name = 'Thread ' + count.ToString();     td[count].Start();     Thread.Sleep(50); } 

Now the only variables being captured in the delegate are copy and runRule/ru/ds – I’m assuming that the latter three don’t change. A new ‘instance’ of the copy variable is created each time you go round the loop, so changes won’t interfere with each other.

See whether this helps – it’s at least a potential cause for massive confusion, and may well be the problem.