.NET multithreading, volatile and memory model
- by fedor-serdukov
Assume that we have the following code:
class Program
{
static volatile bool flag1;
static volatile bool flag2;
static volatile int val;
static void Main(string[] args)
{
for (int i = 0; i < 10000 * 10000; i++)
{
if (i % 500000 == 0)
{
Console.WriteLine("{0:#,0}",i);
}
flag1 = false;
flag2 = false;
val = 0;
Parallel.Invoke(A1, A2);
if (val == 0)
throw new Exception(string.Format("{0:#,0}: {1}, {2}", i, flag1, flag2));
}
}
static void A1()
{
flag2 = true;
if (flag1)
val = 1;
}
static void A2()
{
flag1 = true;
if (flag2)
val = 2;
}
}
}
It's fault! The main quastion is Why... I suppose that CPU reorder operations with flag1 = true; and if(flag2) statement, but variables flag1 and flag2 marked as volatile fields...
