NullReferenceException when using AsyncPool

I’m using FasterWrapper as suggested by https://github.com/microsoft/FASTER/issues/780#issuecomment-1383267812 But when running the following code, which checkpoints from multiple threads, I’m receving a NullReferenceException at var status = session.Upsert(key, value);

Can you please explain why?

var faster = new FasterWrapper<long, long>(isRefType: false, useLargeLog: false, useOsReadBuffering: false);
await Task.WhenAll(Enumerable.Range(0, 2).Select(async i =>
{
    faster.Upsert(i, i);
    await faster.Store.TakeHybridLogCheckpointAsync(CheckpointType.FoldOver);
}));

I’ve also noticed in the synchronous variation of methods like Upsert in FasterWrapper, _sessionPool.GetAsync().GetAwaiter().GetResult() is being used instead of the synchronous _sessionPool.Get(), is there reason for that?

[badrishc]

Fixed in https://github.com/microsoft/FASTER/pull/785

[wassim-k]

Reproduction:

• Checkout AsyncStress playground
• Expose public FasterKV<Key, Value> Store => _store; from FasterWrapper<Key, Value>
• Replace Program’s Main method with above code as is.

Exception:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at FASTER.core.ClientSession`6.InternalFasterSession.TryLockEphemeralExclusive(RecordInfo& recordInfo)
   at AsyncStress.FasterWrapper`2.Upsert(Key key, Value value) in C:\Code\AsyncStress\FasterWrapper.cs:line 87
   at AsyncStress.Program.<>c__DisplayClass10_0.<<Main>b__0>d.MoveNext() in C:\Code\AsyncStress\Program.cs:line 70
--- End of stack trace from previous location ---
   at AsyncStress.Program.Main(String[] args) in C:\Code\AsyncStress\Program.cs:line 68
   at AsyncStress.Program.<Main>(String[] args)

The issue happens in v2.2.0 and v2.3.0 but not in v.2.1.0