C# manual lock/unlock

Question

I have a function in C# that can be called multiple times from multiple threads and I want it to be done only once so I thought about this:

class MyClass
{
          


        

Answer 1

You can check the value of done before and after the lock:

    if (!done)
    {
        lock(this)
        {
            if(!done)
            {
                done = true;
                _DoSomething();
            }
        }
    }

This way you won't enter the lock if done is true. The second check inside the lock is to cope with race conditions if two threads enter the first if at the same time.

BTW, you shouldn't lock on this, because it can cause deadlocks. Lock on a private field instead (like private readonly object _syncLock = new object())