Concurrency Issue

Code USed: Startup.cs

       DeviceDetector.SetVersionTruncation(VersionTruncation.VERSION_TRUNCATION_NONE); 

       var userAgent = context.Request.Headers["User-Agent"]; 

        var deviceDetector = new DeviceDetector(userAgent); 

        deviceDetector.Parse(); 

Issue encounter: System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection’s state is no longer correct.

at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)

at System.Collections.Generic.Dictionary`2.ContainsKey(TKey key)

at DeviceDetectorNET.Cache.DictionaryCache.Contains(String id)

at DeviceDetectorNET.Cache.DictionaryCache.Fetch(String id)

at DeviceDetectorNET.Parser.ParserAbstract`2.GetRegexes()

at DeviceDetectorNET.Parser.Client.LibraryParser…ctor()

at DeviceDetectorNET.Parser.Client.ClientType.get_Library()

at DeviceDetectorNET.DeviceDetector.AddClientsParser()

at DeviceDetectorNET.DeviceDetector…ctor(String userAgent)

[cpkuo]

So I went into the source code to match up with the stack trace for this exception and realized I was using a dotnet core version package of DeviceDetector.NET that I don’t believe exists anymore. Nuget package manager was not notifying me of updating. So I removed it and started using the latest package of DeviceDetector.NET which now supports the latest .net standard. So far, I have not run into this issue.

[cpkuo]

Sure, there is still the possibility that DeviceDetector will write to it’s internal cache collection on concurrent requests but this seems to have helped me in a high load environment. I wonder if setting a new instance of DictonaryCache on each request in combination with the custom ConcurrentDictionary cache will completely eliminate the error. I will need to review the source code at some point, in the meantime here is some code.

`private static ConcurrentDictionary<string, DeviceInfo> cache = new ConcurrentDictionary<string, DeviceInfo>(); private static DictionaryCache dicationaryCache = new DictionaryCache();

public DeviceInfo Get(string userAgent)
{
    if (cache.ContainsKey(userAgent))
    {
        return cache[userAgent];
    }

    //Domain class
    var info = new DeviceInfo();

    DeviceDetector.SetVersionTruncation(VersionTruncation.VERSION_TRUNCATION_NONE);
    var dd = new DeviceDetector(userAgent);

    dd.SetCache(dicationaryCache);
    dd.Parse();

    var client = dd.GetClient();

    //Transfer result into domain class DeviceInfo
    //  .......

    cache.TryAdd(userAgent, info);

    return info;
}`