public static class GlobalVariables
{
    private static readonly object lockObject = new object();
    private static int activeTradeCount = 0;

    public static int ActiveTradeCount
    {
        get
        {
            lock (lockObject)
            {
                return activeTradeCount;
            }
        }
        set
        {
            lock (lockObject)
            {
                activeTradeCount = value;
            }
        }
    }
}

// Check to do before entering a trade in each strategy running concurrently
if (GlobalVariables.ActiveTradeCount == 0)
     GlobalVariables.ActiveTradeCount++;
     // add you code to enter a new trade here