Race condition for thread startup
- by Ozzah
A similar question was asked here, but the answers generally all seem to relate to the lambda notation. I get a similar result without the lambda so I thought I'd ask for some clarification:
Say I have something like this:
for (int i = 0; i < 5; i++)
(new Thread(new ThreadStart(delegate()
{
Console.WriteLine("Thread " + i);
}))).Start();
One would expect the following output:
Thread 0
Thread 1
Thread 2
Thread 3
Thread 4
Now I realise that the threads aren't started in any particular order, so let's just assume that the above lines can come out in any order.
But that is not what happens.
What instead happens:
Thread 3
Thread 4
Thread 4
Thread 4
Thread 4
or something similar, which leads me to believe that rather than passing the value if i, it is passing the reference. (Which is weird, since an int is a value type).
Doing something like this:
for (int i = 0; i < 5; i++)
(new Thread(new ThreadStart(delegate()
{
int j = i;
Console.WriteLine("Thread " + j);
}))).Start();
does not help either, even though we have made a copy of i. I am assuming the reason is that it hasn't made a copy of i in time.
Doing something like this:
for (int i = 0; i < 5; i++)
{
(new Thread(new ThreadStart(delegate()
{
Console.WriteLine("Thread " + i);
}))).Start();
Thread.Sleep(50);
}
seems to fix the problem, however it is extremely undesirable as we're wasting 50ms on each iteration, not to mention the fact that if the computer is heavily loaded then maybe 50ms may not be enough.
Here is a sample with my current, specific problem:
Thread t = new Thread(new ThreadStart(delgate()
{
threadLogic(param1, param2, param3, param4);
}));
t.Start();
param1 = param2 = param3 = param4 = null;
with:
void threadLogic(object param1, object param2, object param3, object param4)
{
// Do some stuff here...
}
I want threadLogic() to run in its own thread, however the above code gives a null reference exception. I assume this is because the values are set to null before the thread has had a chance to start.
Again, putting a Thread.Sleep(100) works, but it is an awful solution from every aspect.
What do you guys recommend for this particular type of race condition?
