从主线程获取后台任务的数据

Question

Here I have got a global variable which stores the index of a for loop. It's a long running process so the for each is done inside a Task . Inside that Task the index value is stored into a variable. While the background process runs I have another method which gets the value from the global variable. But it returns incorrect.

int myCount = -1;
Task BackgroundTask;
List<int> Count = new List<int>();

protected void Run_Click(object sender, EventArgs e)
{
    BackgroundTask = new Task(() =>
        {
            for (int i = 0; i < 1000000; i++)
            {
                myCount = myCount + 1;
                Thread.Sleep(1000);
            }
        });
    BackgroundTask.Start();
}

protected void Check_Click(object sender, EventArgs e)
{
    Count.Add(myCount);            
}

Here while accessing the value of the variable myCount always returns -1 when done with Check_Click method. But the thread is still running. Why is it so and how can I get the count value without making the variable static?

Answer 1

It seems to be related to compiler optimizations. try marking your index variable definition with volatile keyword which informs the compiler about the fact that multiple threads will access the variable.

volatile int myCount = -1;
Task BackgroundTask;
//rest of the code