HttpClient与HttpClientHandler是否销毁？代码重构等价性及资源释放确认

问题描述 #

我想优化现有代码，目前多个API的HttpClient和HttpClientHandler结构相似，但对资源销毁有疑问。我知道using语句可以自动释放这类资源，想问问能不能把代码重构为抽离SetClientSettings方法的版本，重构后的两种写法是否等价，资源能不能始终被正确销毁？

原有代码 #

public static async Task<IEnumerable<T>> deletePostsAsync<T>(IEnumerable<string> urls) where T : BaseReturnValues
{
    var httpClientHandler = new HttpClientHandler
    {
        Proxy = new WebProxy(proxy, true),
        UseProxy = IsProxySelected
    };

    using (var client = new HttpClient(httpClientHandler))
    {
        client.BaseAddress = new Uri(URI);
        client.DefaultRequestHeaders.Clear();
        client.DefaultRequestHeaders.Add(Head.key, Head.apikey);

        var tasks = urls.Select(async url => await DeleteAsync<T>(client, url).ConfigureAwait(false));
        var result = await Task.WhenAll(tasks).ConfigureAwait(false);

        return result!;
    }
    async Task<U> DeleteAsync<U>(HttpClient client, string url) where U : BaseReturnValues
    {
        var statusCode = -1;
        var json = "_";
        var isSuccess = false;

        try
        {
            using (HttpResponseMessage response = await client.DeleteAsync(url).ConfigureAwait(false))
            {
                statusCode = (Int32)response.StatusCode;
                json = await response.Content.ReadAsStringAsync();
                isSuccess = response.IsSuccessStatusCode;
            }
        }
        catch (Exception ex)
        {
            // 异常处理逻辑
        }

        // 省略其他逻辑，返回对应结果
        return record;
    }
}

重构后代码 #

public static async Task<IEnumerable<T>> deletePostsAsync<T>(IEnumerable<string> urls) where T : BaseReturnValues
{
    using (var client = SetClientSettings())
    {
        var tasks = urls.Select(async url => await DeleteAsync<T>(client, url).ConfigureAwait(false));
        var result = await Task.WhenAll(tasks).ConfigureAwait(false);

        return result!;
    }
    async Task<U> DeleteAsync<U>(HttpClient client, string url) where U : BaseReturnValues
    {
        // 省略原有逻辑，返回对应结果
        return record;
    }
}

public static HttpClient SetClientSettings()
{
    var httpClientHandler = new HttpClientHandler
    {
        Proxy = new WebProxy(proxy, true),
        UseProxy = IsProxySelected
    };
    var client = new HttpClient(httpClientHandler);
    client.BaseAddress = new Uri(URI);
    client.DefaultRequestHeaders.Clear();
    client.DefaultRequestHeaders.Add(Head.key, Head.apikey);

    return client;
}

核心疑问 #

以下两段代码是否完全等价？

代码片段1

var httpClientHandler = new HttpClientHandler
{
    Proxy = new WebProxy(proxy, true),
    UseProxy = IsProxySelected
};

using (var client = new HttpClient(httpClientHandler))
{
    client.BaseAddress = new Uri(URI);
    client.DefaultRequestHeaders.Clear();
    client.DefaultRequestHeaders.Add(Head.key, Head.apikey);

    var tasks = urls.Select(async url => await DeleteAsync<T>(client, url).ConfigureAwait(false));
    var result = await Task.WhenAll(tasks).ConfigureAwait(false);

    return result!;
}

代码片段2

using (var client = SetClientSettings())
{
    var tasks = urls.Select(async url => await DeleteAsync<T>(client, url).ConfigureAwait(false));
    var result = await Task.WhenAll(tasks).ConfigureAwait(false);

    return result!;
}

回答 #

• 两段代码完全等价：SetClientSettings方法只是把HttpClientHandler的创建、HttpClient的实例化和配置逻辑抽离出来，本质上和代码片段1做的事情一模一样。重构只是把重复的配置逻辑封装，没有改变对象的生命周期和资源管理方式。另外注意重构后的SetClientSettings方法返回值你写成了Httpclient，大小写错误，需要修正为HttpClient，否则编译不通过。
• 资源销毁完全正确：当using块结束时，HttpClient会被自动调用Dispose方法。通过new HttpClient(httpClientHandler)创建客户端时，默认情况下HttpClient会接管传入的HttpClientHandler的生命周期，在自身Dispose时也会自动释放HttpClientHandler的资源。所以不管是原代码还是重构后的代码，HttpClient和HttpClientHandler都会被正确销毁，不会出现资源泄漏。
• 这个重构是合理的：把重复的客户端配置逻辑抽成公共方法，能有效减少代码冗余，多个API调用都可以复用这个方法，后续修改配置也只需要改一处，维护性更好。

内容的提问来源于stack exchange，提问作者Frenchy