Is C # + = thread safe?

Question

I just came across a program where + = is used for a common variable among threads, so + = is thread safe, i.e. performs addition and assignment atomically?

Answer 1

No, it is not thread safe, as it is equivalent to:

int temp = orig + value; orig = temp; 

Instead, you can use Interlocked.Add :

 Interlocked.Add(ref orig, value); 

Answer 2

Do you want to

 System.Threading.Interlocked.Add() 

Answer 3

 string s += "foo"; 

there is

 string s = s + "foo"; 

s read and then reassigned. If between these two actions the value of s changed by another thread, the result will be different, therefore, it will not be thread safe.

Answer 4

Thanks to everyone for the quick answers. Yes, + = is not thread safe and the following simple program may be run to verify this.

int count = 0;

  Parallel.For(0, 10000, i => { count +=1; // not thread safe }); Console.WriteLine(count); 

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