Question

I need to implement simple function that is called from multiple threads. The logic of the function is simple – think of horse races – only the first horse can get golden medal once we have a winner the race is over.

class ConditionalOrderGroup
{
    private volatile bool _locked = false;
    private List<ConditionalOrder> _ConditionalOrderList = null;        

public bool LockGroup(ConditionalOrder initiator)
{
   // this is finishline - we need to let only the first one proceed
    if (_locked)
        return false;
    else
    {
        _locked = true;
    }

    // this is what winner gets
    foreach (ConditionalOrder order in _ConditionalOrderList)
    {

      \\ cancel other orders
    }

    return true;
}
}

I am not happy with

if (_locked)
    return false;
else
{
    _locked = true;
}

What if two orders can pass if check and proceed to else. How to rewrite this code
without using lock statement?

UPDATE
I mean my goal is not use any blocking method like lock statement.

Answer 1

You need a separate, private object and use the built-in locking:

private object padLock = new object();  // 1-to-1 with _ConditionalOrderList

if (Monitor.TryEnter(padLock))
{
   try 
   {
      // cancel other orders

      return true;
   } 
   finally 
   {
       Monitor.Exit(padLock);
   }
}
else
{
   return false;
}