[GitHub] [tinkerpop] jorgebay commented on issue #1077: TINKERPOP-2135 Fix handling of closed idle connections in Gremlin.Net driver

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jorgebay commented on issue #1077: TINKERPOP-2135 Fix handling of closed idle connections in Gremlin.Net driver
URL: https://github.com/apache/tinkerpop/pull/1077#issuecomment-470084590
 
 
   > What's the advantage of such a custom copy-on-write list?
   
   Any read operation is cheap and the iterator is not affected by concurrent modifications (unlike concurrent collections). Effectively what you get is a moment-in-time view of the collection, you don't have to add special conditions to track concurrent changes.
   
   About using a queue, IMO we shouldn't rely on that sort of behaviour here (I think we discussed a similar queue approach for the pool in https://github.com/apache/tinkerpop/pull/903):
   - We should support concurrent writes to the connection, if we queue it and dequeue it, we might end up with an empty pool (at a certain time). We might need complicated logic to guard for that.
   - Using a enqueuing/dequeueing from a concurrent queue is not a cheap operation when multiple threads are accessing to it. We will be introducing unnecessary overhead.
   - We shouldn't iterate through all the connections when borrowing from the pool, we just need to round robin through them, sample pseudo code: 
   
   ```C#
   // obtain something that is fixed for this small period of time
   IList<Connection> immutableCopyOfConnections = ... 
   int counter = Interlocked.Increment(ref _sharedCounter);
   int index = counter % immutableCopyOfConnections.Count;
   return immutableCopyOfConnections[index];
   ```
   
   If we need to compare the one with least in-flight requests, we should minimize the amount of checks, for example check connections at `index` and `index+1`, instead of checking the whole list (`O(2)` vs `O(n)`).
   
   > Do you know whether the default `TaskScheduler` would work here?
   
   No, we will need a custom one like `LimitedConcurrencyLevelTaskScheduler`.

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