Hi, 

During using the MongoDrive, I encounter a deadlock issue which cause the whole application loading data blocked. After doing few research, I figured out the issue was caused by two collections had the same generic parameters, but different dictionary representaion properties. 

Two threads' call stack as follows:

 
A Thread:
-> DictionarySerializerBase<TDictionary, TKey, TValue>.DeserializeValue
-> Lazy<T>.CreateValue
-> Lazy<T>.ExecutionAndPublication
-> Lazy<T>.ViaFactory
-> BsonSerializerRegistry.GetSerializer
-> BsonClassMapSerializationProvider.GetSerializer
-> BsonClassMap.LookupClassMap
-> BsonSerializer.ConfigLock.EnterReadLock (deadlock)

B Thread：
-> BsonSerializerRegistry.CreateSerializer
-> BsonClassMap.LookupClassMap
-> BsonSerializer.ConfigLock.EnterWriteLock
-> BsonClassMap.AutoMap
-> AttributeConventionPack+AttributeConvention.Apply
-> DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>.WithDictionaryRepresentation
-> DictionarySerializerBase.get_ValueSerializer
-> Lazy<T>.CreateValue
-> Lazy<T>.ExecutionAndPublication (deadlock)
 

1. Thread A first used the default seirializer and registered the DictionaryInterfaceImplementerSerializer

** BsonSerializerRegistry.

**

 
2. Tread B then used the non-default seirializer. The thread got the readlock and need to get a instance from the DictionaryInterfaceImplementerSerializer which need to visit ** its *

*

This bug can reproduced by the code below 
 

var testData = new TestData { Items = new Dictionary<string, Item>() { { "1", new Item() } } };
var testData2 = new TestData2 { Items = new Dictionary<string, Item>() { { "2", new Item() } } };

BsonSerializer.SerializerRegistry.GetSerializer<Dictionary<int, Item>>();

_ = Task.Run(() =>
{
    var stream = new MemoryStream();
    using var bsonWriter = new BsonBinaryWriter(stream);
    BsonSerializer.Serialize(bsonWriter, testData);
});

await Task.Delay(TimeSpan.FromMilliseconds(100));

{
    var stream = new MemoryStream();
    using var bsonWriter = new BsonBinaryWriter(stream);
    BsonSerializer.Serialize(bsonWriter, testData2);
}

Console.WriteLine("Hello, World!");

public class Item;

public class TestData
{
    public Dictionary<string, Item> Items { get; set; } = new();
}

public class TestData2
{
    [BsonDictionaryOptions(DictionaryRepresentation.ArrayOfArrays)]
    public Dictionary<string, Item> Items { get; set; } = new();
}

The modification in the driver as the attachment shows can also increase the probibility to reproduce this issue.
 
Best Regards.
Renqiu