C#•2y ago

❔ ConfigureAwait(false) (IntelliCode Suggestion)

Can someone help me to understand why IntelliCode is suggesting ConfigureAwait(false) at line 16 await Dns.GetHostEntryAsync(ipAddress);? Would this really result in an advantage?

private async Task<List<DeviceInfo>> GetDevices(XDocument xDocument)
{
    List<DeviceInfo> deviceList = new List<DeviceInfo>();

    var itemElements = xDocument.Descendants("item");
    foreach (var itemElement in itemElements)
    {
        string? deviceName = itemElement.Element("device")?.Value;
        string? host = itemElement.Element("host")?.Value;
        string? objId = itemElement.Element("objid")?.Value;

        if (IPAddress.TryParse(host, out IPAddress? ipAddress) && ipAddress.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
        {
            try
            {
                var hostEntry = await Dns.GetHostEntryAsync(ipAddress);
                host = hostEntry.HostName;
            }
            catch
            {
                _logger.LogError($"There is an error occured while resolving {ipAddress}: {host}");
            }
        }

        // remove all possible domains from FQDNs to get hostnames even if they include dots
        if (_optionsAccessor.PossibleOccuringDomains is not null && !string.IsNullOrEmpty(host))
        {
            deviceName = host;
            _optionsAccessor.PossibleOccuringDomains.ForEach(item =>
            {
                deviceName = deviceName.Replace(item, string.Empty);
            });
        }

        deviceList.Add(new DeviceInfo { HostName = deviceName, FQDN = host, ObjID = objId });
    }
    return deviceList;
}

private async Task<List<DeviceInfo>> GetDevices(XDocument xDocument)
{
    List<DeviceInfo> deviceList = new List<DeviceInfo>();

    var itemElements = xDocument.Descendants("item");
    foreach (var itemElement in itemElements)
    {
        string? deviceName = itemElement.Element("device")?.Value;
        string? host = itemElement.Element("host")?.Value;
        string? objId = itemElement.Element("objid")?.Value;

        if (IPAddress.TryParse(host, out IPAddress? ipAddress) && ipAddress.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
        {
            try
            {
                var hostEntry = await Dns.GetHostEntryAsync(ipAddress);
                host = hostEntry.HostName;
            }
            catch
            {
                _logger.LogError($"There is an error occured while resolving {ipAddress}: {host}");
            }
        }

        // remove all possible domains from FQDNs to get hostnames even if they include dots
        if (_optionsAccessor.PossibleOccuringDomains is not null && !string.IsNullOrEmpty(host))
        {
            deviceName = host;
            _optionsAccessor.PossibleOccuringDomains.ForEach(item =>
            {
                deviceName = deviceName.Replace(item, string.Empty);
            });
        }

        deviceList.Add(new DeviceInfo { HostName = deviceName, FQDN = host, ObjID = objId });
    }
    return deviceList;
}

18 Replies

kocha•2y ago

It would increase performance, but unless you know exactly what it is doing, i would nod recommend it.

Connor•2y ago

It wouldn’t increase performance. It would change the synchronization context that the callback uses.

kocha•2y ago

Yes, but to change the synchronisation context takes a bit of time, so not doing it increases performance If you actually have one, which is only really the case in gui applications

Connor•2y ago

I guess your right

mtreit•2y ago

The suggestion has little to do with performance. It's a best practice to always use ConfigureAwait(false) if you are writing code in a library that does not need to capture the syncrhonization context. It avoids the possibility of deadlocks if some consumer of your code decides to call .Result or .Wait (which is usually a poor practice, but it happens in the real world all the time.)

kocha•2y ago

I would disagree, microsoft themself say that the reason is performance and deadlock related: https://devblogs.microsoft.com/dotnet/configureawait-faq/

Stephen Toub - MSFT

.NET Blog

ConfigureAwait FAQ - .NET Blog

.NET added async/await to the languages and libraries over seven years ago. In that time, it’s caught on like wildfire, not only across the .NET ecosystem, but also being replicated in a myriad of other languages and frameworks. It’s also seen a ton of improvements in .NET,

mtreit•2y ago

I'm familiar with that post and I agree with everything in it. Just that performance is not the primary reason to use ConfigureAwait(false)...

kocha•2y ago

Ok, i see

mtreit•2y ago

I wonder if I have a benchmark for this...

kocha•2y ago

Depends 100% on what the synchronisation context actually does.

mtreit•2y ago

Ah yes, I do

mtreit•2y ago

https://github.com/Treit/MiscBenchmarks/blob/main/ConfigureAwait/README.md

GitHub

MiscBenchmarks/ConfigureAwait/README.md at main · Treit/MiscBenchma...

Contribute to Treit/MiscBenchmarks development by creating an account on GitHub.

kocha•2y ago

This is a console app, it doesnt even have a synchronisation context, or am im I missing something

mtreit•2y ago

It has the default synchronization context (which is the thread pool) It's entirely possible that it's a noop for the default task scheduler I never checked Although the benchmark numbers do seem to show that ConfigureAwait(true) has some small overhead

mtreit•2y ago

mtreit•2y ago

Congratulations @kocha you have lead me down a complete rabbit hole: https://discord.com/channels/143867839282020352/143867839282020352/1133887368131264532

MODiX•2y ago

mtreit

public long ReadAsyncAwaitCustomContextConfigureAwaitFalse()
{
    long result = 0;

    using var sr = new StreamReader(_testFile);

    string line;

    while ((line = AsyncContext.Run(async () => { var res = await sr.ReadLineAsync().ConfigureAwait(false); Console.WriteLine($"{res} -> {SynchronizationContext.Current?.GetType().Name ?? "<null>"}"); return res; })) != null)
    {
        result += int.Parse(line);
    }

    return result;
}

public long ReadAsyncAwaitCustomContextConfigureAwaitFalse()
{
    long result = 0;

    using var sr = new StreamReader(_testFile);

    string line;

    while ((line = AsyncContext.Run(async () => { var res = await sr.ReadLineAsync().ConfigureAwait(false); Console.WriteLine($"{res} -> {SynchronizationContext.Current?.GetType().Name ?? "<null>"}"); return res; })) != null)
    {
        result += int.Parse(line);
    }

    return result;
}

I have a two line file. Literally these bytes:

          Offset Bytes                                           Ascii
                 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          ------ ----------------------------------------------- -----
0000000000000000 30 0D 0A 31 0D 0A                               0��1��

          Offset Bytes                                           Ascii
                 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
          ------ ----------------------------------------------- -----
0000000000000000 30 0D 0A 31 0D 0A                               0��1��

If I feed this file to the above code, what does it print out?

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Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ ConfigureAwait(false) (IntelliCode Suggestion)

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