I need to implement the class that should perform locking mechanism in our framework. We have several threads and they are numbered 0,1,2,3.... We have a static class called ResourceHandler, that should lock these threads on given objects. The requirement is that n Lock() invokes should be realeased by m Release() invokes, where n = [0..] and m = [0..]. So no matter how many locks was performed on single object, only one Release call is enough to unlock all. Even further if o object is not locked, Release call should perform nothing. Also we need to know what objects are locked on what threads.

I have this implementation:

public class ResourceHandler
{
    private readonly Dictionary<int, List<object>> _locks = new Dictionary<int, List<object>>();

    public static ResourceHandler Instance {/* Singleton */}

    public virtual void Lock(int threadNumber, object obj)
    {
        Monitor.Enter(obj);

        if (!_locks.ContainsKey(threadNumber)) {_locks.Add(new List<object>());}
        _locks[threadNumber].Add(obj);
    }

    public virtual void Release(int threadNumber, object obj)
    {
       // Check whether we have threadN in _lock and skip if not
       var count = _locks[threadNumber].Count(x => x == obj);
       _locks[threadNumber].RemoveAll(x => x == obj);

       for (int i=0; i<count; i++)
       {
           Monitor.Exit(obj);
       }
    }

    // .....
 }

Actually what I am worried here about is thread-safety. I'm actually not sure, is it thread-safe or not, and it's a real pain to fix that. Am I doing the task correctly and how can I ensure that this is thread-safe?