Florian Hockmann created TINKERPOP-2135:
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Summary: Gremlin.Net ConnectionPool doesn't handle closed idle
connections properly
Key: TINKERPOP-2135
URL: https://issues.apache.org/jira/browse/TINKERPOP-2135
Project: TinkerPop
Issue Type: Bug
Affects Versions: 3.4.0
Reporter: Florian Hockmann
The {{ConnectionPool}} of Gremlin.Net checks whether a connection is actually
still open before it returns that connection to execute a request ([in
{{SelectLeastUsedConnection}}|https://github.com/apache/tinkerpop/blob/67764ba23d67d9f62048c22e8bbcefb87463584e/gremlin-dotnet/src/Gremlin.Net/Driver/ConnectionPool.cs#L124]):
{code}
if (connection.IsOpen) return true;
DefinitelyDestroyConnection(connection);
{code}
However, the connection stays in the pool as {{DefinitelyDestroyConnection}}
only disposes the connection:
{code}
private void DefinitelyDestroyConnection(Connection connection)
{
connection.Dispose();
Interlocked.Decrement(ref _nrConnections);
}
{code}
This is problematic as it can potentially fill the pool with unusable
connections. Even worse, {{SelectLeastUsedConnection}} will likely return such
an unusable connection since it only checks for the number of in-flight
requests and a disposed connection won't have any in-flight requests. This
should ultimately result in a {{NoConnectionAvailableException}} when the pool
tried {{_poolSize}} times to return such a disposed connection.
Note: This all can only happen when a connection was closed while sitting idle
in the pool which shouldn't usually happen due to the heartbeat. If a
connection problem occurs during the execution of a request, then all
connections will be closed and new ones will be created.
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