C#任务总和变量

Question

我有以下任务,他们共享sum变量,最后总和应该是9,但我得到3.你能帮我解决一下吗？非常感谢.

int sum = 0;
Task t1 = Task.Factory.StartNew(() =>
{
    sum = sum + Computation();
});
Task t2 = Task.Factory.StartNew(() =>
{
    sum = sum + Computation();
});
Task t3 = Task.Factory.StartNew(() =>
{
    sum = sum + Computation();
});

Task.WaitAll(t1, t2, t3);
Console.WriteLine($"The sum is {sum}");

private static int Computation()
{
    return 3;
}

Answer 1

这是因为你在同一时间从多个线程编写相同的字段.

使用System.Threading中的Interlocked.Add,这将阻止每个线程在同一时刻写入变量.

int sum = 0;
Task t1 = Task.Factory.StartNew(() =>
{
     Interlocked.Add(ref sum,Computation());
});
Task t2 = Task.Factory.StartNew(() =>
{
     Interlocked.Add(ref sum,Computation());
});
Task t3 = Task.Factory.StartNew(() =>
{
     Interlocked.Add(ref sum,Computation());
});

Task.WaitAll(t1, t2, t3);
Console.WriteLine($"The sum is {sum}");