Exception "Destination array is not long enough to copy all the items in the collection. Check array index and length." happens in when running under debugger

[SergeyKanzhelev]

Exception "Destination array is not long enough to copy all the items in the collection. Check array index and length." happens in when running under debugger:

System.ArgumentException occurred
  HResult=-2147024809
  Message=Destination array is not long enough to copy all the items in the collection. Check array index and length.
  Source=mscorlib
  StackTrace:
       at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
       at System.Collections.Generic.Dictionary`2.CopyTo(KeyValuePair`2[] array, Int32 index)
       at System.Collections.Generic.Dictionary`2.System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>.CopyTo(KeyValuePair`2[] array, Int32 index)
       at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
       at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
       at Microsoft.ApplicationInsights.Extensibility.Implementation.Property.SanitizeProperties(IDictionary`2 dictionary)
       at Microsoft.ApplicationInsights.DataContracts.EventTelemetry.Microsoft.ApplicationInsights.Channel.ITelemetry.Sanitize()
       at Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SeializeToStream(IEnumerable`1 telemetryItems, TextWriter streamWriter)
       at Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SerializeAsString(IEnumerable`1 telemetryItems)
       at Microsoft.ApplicationInsights.Extensibility.Implementation.TelemetryDebugWriter.WriteTelemetry(ITelemetry telemetry, String filteredBy)
       at Microsoft.ApplicationInsights.Extensibility.Implementation.TransmissionProcessor.Process(ITelemetry item)
       at Microsoft.ApplicationInsights.WindowsServer.Channel.Implementation.SamplingPercentageEstimatorTelemetryProcessor.Process(ITelemetry item)
       at Microsoft.ApplicationInsights.WindowsServer.TelemetryChannel.SamplingTelemetryProcessor.Process(ITelemetry item)
       at Microsoft.ApplicationInsights.WindowsServer.TelemetryChannel.AdaptiveSamplingTelemetryProcessor.Process(ITelemetry item)
       at Microsoft.ApplicationInsights.TelemetryClient.Track(ITelemetry telemetry)
       at Microsoft.ApplicationInsights.TelemetryClient.TrackEvent(EventTelemetry telemetry)
       at Microsoft.ApplicationInsights.TelemetryClient.TrackEvent(String eventName, IDictionary`2 properties, IDictionary`2 metrics)

The probable root cause is that Debug writer executes in parallel with the channel. Both of them doing sanitization by modifying the same collection in parallel.

[SergeyKanzhelev]

Another exception you can get is:

System.InvalidOperationException occurred
  HResult=-2146233079
  Message=Collection was modified; enumeration operation may not execute.
  Source=mscorlib
  StackTrace:
       at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
  InnerException: 

    mscorlib.dll!System.ThrowHelper.ThrowInvalidOperationException(System.ExceptionResource resource)   Unknown
    mscorlib.dll!System.Collections.Generic.Dictionary<string, string>.Enumerator.MoveNext()    Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.JsonWriter.WriteProperty(string name, System.Collections.Generic.IDictionary<string, string> values)   Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SerializeEventTelemetry(Microsoft.ApplicationInsights.DataContracts.EventTelemetry eventTelemetry, Microsoft.ApplicationInsights.Extensibility.Implementation.JsonWriter writer)    Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SerializeTelemetryItem(Microsoft.ApplicationInsights.Channel.ITelemetry telemetryItem, Microsoft.ApplicationInsights.Extensibility.Implementation.JsonWriter jsonWriter)    Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SeializeToStream(System.Collections.Generic.IEnumerable<Microsoft.ApplicationInsights.Channel.ITelemetry> telemetryItems, System.IO.TextWriter streamWriter)    Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.JsonSerializer.SerializeAsString(System.Collections.Generic.IEnumerable<Microsoft.ApplicationInsights.Channel.ITelemetry> telemetryItems)  Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.TelemetryDebugWriter.WriteTelemetry(Microsoft.ApplicationInsights.Channel.ITelemetry telemetry, string filteredBy) Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.Extensibility.Implementation.TransmissionProcessor.Process(Microsoft.ApplicationInsights.Channel.ITelemetry item)   Unknown
    Microsoft.ApplicationInsights.dll!Microsoft.ApplicationInsights.TelemetryClient.Track(Microsoft.ApplicationInsights.Channel.ITelemetry telemetry)   Unknown
>   ConsoleApplication5.exe!ConsoleApplication5.Program.Main(string[] args) Line 55 C#

Repro code:

    class Program
    {
        static Random random = new Random();

        public static string RandomString(int length)
        {
            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789#-*\"#-*\"#-*\"#-*\"#-*\"#-*\"#-*\"#-*\"#-*\"#-*\"";

            return new string(Enumerable.Repeat(chars, length)
              .Select(s => s[random.Next(s.Length)]).ToArray());
        }


        static void Main(string[] args)
        {
            TelemetryConfiguration.Active.TelemetryChannel.DeveloperMode = true;

            TelemetryClient client = new TelemetryClient();
            client.InstrumentationKey = "9d3ebb4f-7a11-4fb1-91ac-7ca8a17627eb";

            Random r = new Random();

            var counter = 0;

            while (true)
            {
                EventTelemetry telemetry = new EventTelemetry();

                int len = r.Next(50);

                for (int i = 0; i < len; i++)
                {
                    string key = RandomString(10);
                    if (!telemetry.Properties.ContainsKey(key))
                        telemetry.Properties.Add(key, RandomString(50));

                    Debug.WriteLine(key +" " + telemetry.Properties[key]);
                }

                Thread.Sleep(1000);
                client.Track(telemetry);
                //((ITelemetry)telemetry).Sanitize();

                Debug.WriteLine(counter++.ToString() + " len: " + len);
            }

        }
    }

[abaranch]

@SergeyKanzhelev Please merge the fix to master. We want to have it in the next stable version.

[SergeyKanzhelev]

Workaround is to set this flag:

TelemetryDebugWriter.IsTracingDisabled = true;