Do HttpClient and HttpClientHandler have to be disposed between requests?

Question

System.Net.Http.HttpClient and System.Net.Http.HttpClientHandler in .NET Framework 4.5 implement IDisposable (via System.Net.Http.HttpMessageInvoker).

The usin

Answer 1

If you want to dispose of HttpClient, you can if you set it up as a resource pool. And at the end of your application, you dispose your resource pool.

Code:

// Notice that IDisposable is not implemented here!
public interface HttpClientHandle
{
    HttpRequestHeaders DefaultRequestHeaders { get; }
    Uri BaseAddress { get; set; }
    // ...
    // All the other methods from peeking at HttpClient
}

public class HttpClientHander : HttpClient, HttpClientHandle, IDisposable
{
    public static ConditionalWeakTable _httpClientsPool;
    public static HashSet _uris;

    static HttpClientHander()
    {
        _httpClientsPool = new ConditionalWeakTable();
        _uris = new HashSet();
        SetupGlobalPoolFinalizer();
    }

    private DateTime _delayFinalization = DateTime.MinValue;
    private bool _isDisposed = false;

    public static HttpClientHandle GetHttpClientHandle(Uri baseUrl)
    {
        HttpClientHander httpClient = _httpClientsPool.GetOrCreateValue(baseUrl);
        _uris.Add(baseUrl);
        httpClient._delayFinalization = DateTime.MinValue;
        httpClient.BaseAddress = baseUrl;

        return httpClient;
    }

    void IDisposable.Dispose()
    {
        _isDisposed = true;
        GC.SuppressFinalize(this);

        base.Dispose();
    }

    ~HttpClientHander()
    {
        if (_delayFinalization == DateTime.MinValue)
            _delayFinalization = DateTime.UtcNow;
        if (DateTime.UtcNow.Subtract(_delayFinalization) < base.Timeout)
            GC.ReRegisterForFinalize(this);
    }

    private static void SetupGlobalPoolFinalizer()
    {
        AppDomain.CurrentDomain.ProcessExit +=
            (sender, eventArgs) => { FinalizeGlobalPool(); };
    }

    private static void FinalizeGlobalPool()
    {
        foreach (var key in _uris)
        {
            HttpClientHander value = null;
            if (_httpClientsPool.TryGetValue(key, out value))
                try { value.Dispose(); } catch { }
        }

        _uris.Clear();
        _httpClientsPool = null;
    }
}

var handler = HttpClientHander.GetHttpClientHandle(new Uri("base url")).

• HttpClient, as an interface, can't call Dispose().
• Dispose() will be called in a delayed fashion by the Garbage Collector. Or when the program cleans up the object through its destructor.
• Uses Weak References + delayed cleanup logic so it remains in use so long as it is being reused frequently.
• It only allocates a new HttpClient for each base URL passed to it. Reasons explained by Ohad Schneider answer below. Bad behavior when changing base url.
• HttpClientHandle allows for Mocking in tests