Are Session and Cache variables thread safe?

MadWithPowerShell · February 19, 2019, 5:52pm

How thread safe are the Session and Cache variables?

If I have one endpoint testing an integer variable every 50 milliseconds to see when a different endpoint changes it, can the get sometimes interfere with the set? I’m seeing some odd, intermittent behavior that fits that explanation.

Instead of a simple integer, should I use a variable type designed for multithreading, such as a ConcurrentDictionary?

Thanks,
Tim Curwick

adam · February 22, 2019, 3:02am

The Session and Cache variables use the Memory Cache C# type for storage.

github.com

ironmansoftware/universal-dashboard/blob/master/src/UniversalDashboard/Execution/SessionDriveProvider.cs#L90


{
    var item = _memoryCache.Get(ConnectionId + name);
    if (item != null)
    {
        base.WriteItemObject(item, name, false);
    }
}


protected override void NewItem(string path, string itemTypeName, object newItemValue)
{
    _memoryCache.Set(ConnectionId + path, newItemValue);
}


protected override void SetItem(string name, object value)
{
    _memoryCache.Set(ConnectionId + name, value);
}


protected override bool ItemExists(string path)
{
    return _memoryCache.TryGetValue(ConnectionId + path, out object val);

This type is thread safe and you should be able to get and set values without the get interfering with the set.

There is a chance that the interaction between the PS provider API and the memory cache itself is causing some weird threading issues but I would have to dig into it to see what is going on there. If you have a simple reproduction step for this it would be very helpful.