c# - What options do i have to make this code thread safe? -

I have this segment of code, a lot of things have been left for brevity but this is the view:

  public class billing {personal list & lt; PrecalculateValue & gt; Value = new list & lt; Presetulit Value & gt; (); Public Intuit Gateway (date time) {var preCalculated = Values.SingleOrDefault (g = & gt; g.date == date). value; // If the values ​​are present then return it (preCalculated! = Null) {PreCalculated back; } // If it does not exist, then store it in the calculation and values ​​= GetValueFor (date); value. Add (New Spratch Value {date = date, value = value}); return value; } Private object GetValueFor (DateTime date) {// some logic here}}  

I have a list & lt; PrecalculateValue & gt; Values ​​ Where I already store all the values ​​calculated for later use, I do this for these main reasons because I do not want to re-run twice for the same customer, Each calculation involves a lot of operations and 500 and 1000 ms, and because of some recursions included in the holes billing class, there is a great chance to reuse that value.

All these work completely until I did a test, where I had two simultaneous calculating clients for two different calculations, and line value. Single (g = & gt; g.date == date). Value returned an exception because it found more than one result in the collection. So I checked the list and stored values ​​of both clients in the same list can I do to avoid this small problem?

OK, firstly, this line:

  return value . Single (G = & gt; GDD == date). value;  

It does that the subsequent lines will never call. Do you anticipate that you have made your code a little smaller?

If you want to synchronize while typing in your values ​​ list, then the easiest way would be to lock it on a normal object everywhere in that code Which you are modifying the list:

  int value = GetValueFor (date); Lock (dedicated lockObject) {value. Add (new subkey value {date = date, value = value}); }  return value;  

But here's something to be noticeable: because it looks like you want a PrecalculateValue per date time , a more appropriate data structure Maybe the dictionary is - Based on your DateTime key, will provide lightning-fast, o (1) lookups against <(code)> list & lt; PrecalculateValue & gt; have to be repeated to find what you are looking for.

With this change, your code might look like this:

  Public class billing {personal dictionary & lt; Date time, anterior value & gt; Value = New Dictionary & lt; Date time, anterior value & gt; (); Private Redoni normal lock object = new object (); Public Int Gate Value (Datetime Date) {Precqualet Value Cache Clauses; // Note: For the right thread protection, you need to lock / write as well as read, to ensure that with a script / reading / corrupted status / lock (normal lock object) {if (Value, telegraph value (date, cached calculation)) back cached communication. value; } Int Value = GetValueFor (date); // Here we have to check whether the key is present again, just another thread added an item because we checked for the last time. // Also make sure to lock any place you are adding to reading or reading the collection. Lock (normal lock object) {if (! Value (insert value (date)) value [date] = new presetlicate value {date = date, value = value}; }          return value; } Private Object GetValueFor (DateTime date) {// some logic here}}  

And one last advice: unless it is not important that your collection does not exceed any particular value , The single method is overkill if you not only get the first value and ignore the potential duplicate, both of the first are safe (as a low chance of an exception) and It's fast (because it is not recurring on the whole collection).