Comments by _Nizar (Top 4 by date)

The data are not static.
Now after some investigation I found that when I run the code using the debugger so I give all the tasks time to finish before the next task will begin very thing work fine.
But if I run the code using also the debugger but with out giving the firs task time to finish before the next task the last task runs twice so a conflicting happen and the first task never runs.
I'm ready to give my program for investigation.
I have only this problem ales it is working fine in sequence.

thank you for your support

the tasks are independent from each other

Using lock statement will be benefit if I'm using one object and i access its method from many threads.
But in my case I'm using one object per Task they share nothing, so why the access the same property (class variable).
I want to publish my program here but after i have fixed this problem.