sergeykonkin/AsyncMonitor

AsyncMonitor

Inspired by and based on Stephen Cleary's AsyncEx library. The difference is this implementation takes an external object as parameter to EnterAsync and Exit methods. This is useful when the lock object is dynamically defined at runtime.

The purpose of reinventing the wheel was a problem of accessing cacheable resources. Quick example:

public class CachingFileReader : IFileReader
{
    private readonly IDictionary<string, byte[]> _cache;
    private readonly IFileReader _fileReader;

    public CachingFileReader(IFileReader fileReader)
    {
        _cache = new ConcurrentDictionary<string,byte[]>();
        _fileReader = fileReader;
    }

    public async Task<byte[]> ReadAsync(string fileName)
    {
        if (_cache.ContainsKey(fileName))
            return _cache[fileName];

        using (await AsyncMonitor.EnterAsync(fileName))
        {
            // double check cache since it can be populated in another thread
            if (_cache.ContainsKey(fileName))
                return _cache[fileName];

            var fileData = await _fileReader.ReadAsync(fileName);
            _cache[fileName] = fileData;
            return fileData;
        }
    }
}

Instalation

No NuGet for now. Feel free to just grab the single AsyncMonitor.cs file.