前言

官方文檔對 HttpClientHandler.MaxConnectionsPerServer 屬性有如下說明：

獲取或設置使用 HttpClient 對象發出請求時允許的最大并發連接數（每個服務器終結點）。請注意，該限制針對每個服務器終結點，例如，值為 256 表示允許 256 個到 http://www.adatum.com/ 的并發連接，以及另外 256 個到 http://www.adventure-works.com/ 的并發連接。

有網友在交流群中詢問，終結點到底指的啥，怎么判斷是同一終結點？

讓我們通過源碼來看看吧！

源碼分析

HttpClientHandler.MaxConnectionsPerServer

HttpClientHandler.MaxConnectionsPerServer 的實現代碼如下：

public?int?MaxConnectionsPerServer
{get?=>?_underlyingHandler.MaxConnectionsPerServer;set?=>?_underlyingHandler.MaxConnectionsPerServer?=?value;
}

實際使用的是_underlyingHandler.MaxConnectionsPerServer。而_underlyingHandler是SocketsHttpHandler類的實例:

using?HttpHandlerType?=?System.Net.Http.SocketsHttpHandler;private?readonly?HttpHandlerType?_underlyingHandler;

SocketsHttpHandler.MaxConnectionsPerServer

SocketsHttpHandler.MaxConnectionsPerServer 的實現代碼如下：

public?int?MaxConnectionsPerServer
{get?=>?_settings._maxConnectionsPerServer;set{..._settings._maxConnectionsPerServer?=?value;}
}

實際使用的是_settings._maxConnectionsPerServer。那么，誰在使用這個設置值呢？

HttpConnectionPool

我們定位到了HttpConnectionPool的構造函數：

public?HttpConnectionPool(HttpConnectionPoolManager?poolManager,?HttpConnectionKind?kind,?string??host,?int?port,?string??sslHostName,?Uri??proxyUri)
{..._maxHttp11Connections?=?Settings._maxConnectionsPerServer;...
}

而HttpConnectionPool的作用就是，提供到同一終結點的連接池。看來我們離真相越來越近了。

///?<summary>Provides?a?pool?of?connections?to?the?same?endpoint.</summary>
internal?sealed?class?HttpConnectionPool?:?IDisposable

HttpConnectionPoolManager

HttpConnectionPool的構造函數只在HttpConnectionPoolManager類中被調用：

public?ValueTask<HttpResponseMessage>?SendAsyncCore(HttpRequestMessage?request,?Uri??proxyUri,?bool?async,?bool?doRequestAuth,?bool?isProxyConnect,?CancellationToken?cancellationToken)
{HttpConnectionKey?key?=?GetConnectionKey(request,?proxyUri,?isProxyConnect);HttpConnectionPool??pool;while?(!_pools.TryGetValue(key,?out?pool)){pool?=?new?HttpConnectionPool(this,?key.Kind,?key.Host,?key.Port,?key.SslHostName,?key.ProxyUri);

可以看到，HttpConnectionPool是從ConcurrentDictionary _pools 中獲取的，而key的值是HttpConnectionKey類型。

HttpConnectionKey

而 HttpConnectionKey 是這樣判斷是否相等的：

public?readonly?HttpConnectionKind?Kind;
public?readonly?string??Host;
public?readonly?int?Port;
public?readonly?string??SslHostName;?????//?null?if?not?SSL
public?readonly?Uri??ProxyUri;
public?readonly?string?Identity;public?bool?Equals(HttpConnectionKey?other)?=>Kind?==?other.Kind?&&Host?==?other.Host?&&Port?==?other.Port?&&ProxyUri?==?other.ProxyUri?&&SslHostName?==?other.SslHostName?&&Identity?==?other.Identity;

結論

由上面的代碼，我們可以得出如下結論：

如果連接類型、服務器地址、服務器端口、代理（如果有）全部相同，則認為是同一終結點

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