public ExpiredHandlerTrackingEntry(ActiveHandlerTrackingEntry other) { Name = other.Name; _livenessTracker = new WeakReference(other.Handler); InnerHandler = other.Handler.InnerHandler; }
在其构造方法内部，handler对象通过弱引用方式关联着，不会影响其被GC释放。
然后新建的ExpiredHandlerTrackingEntry对象被放入专用的队列。
最后开始清理工作，定时器的时间间隔设定为每10秒一次。
internal void CleanupTimer_Tick(object state) { // Stop any pending timers, we'll restart the timer if there's anything left to process after cleanup. // // With the scheme we're using it's possible we could end up with some redundant cleanup operations. // This is expected and fine. // // An alternative would be to take a lock during the whole cleanup process. This isn't ideal because it // would result in threads executing ExpiryTimer_Tick as they would need to block on cleanup to figure out // whether we need to start the timer. StopCleanupTimer(); try { if (!Monitor.TryEnter(_cleanupActiveLock)) { // We don't want to run a concurrent cleanup cycle. This can happen if the cleanup cycle takes // a long time for some reason. Since we're running user code inside Dispose, it's definitely // possible. // // If we end up in that position, just make sure the timer gets started again. It should be cheap // to run a 'no-op' cleanup. StartCleanupTimer(); return; } var initialCount = _expiredHandlers.Count; Log.CleanupCycleStart(_logger, initialCount); var stopwatch = ValueStopwatch.StartNew(); var disposedCount = 0; for (var i = 0; i < initialCount; i++) { // Since we're the only one removing from _expired, TryDequeue must always succeed. _expiredHandlers.TryDequeue(out var entry); Debug.Assert(entry != null, "Entry was null, we should always get an entry back from TryDequeue"); if (entry.CanDispose) { try { entry.InnerHandler.Dispose(); disposedCount++; } catch (Exception ex) { Log.CleanupItemFailed(_logger, entry.Name, ex); } } else { // If the entry is still live, put it back in the queue so we can process it // during the next cleanup cycle. _expiredHandlers.Enqueue(entry); } } Log.CleanupCycleEnd(_logger, stopwatch.GetElapsedTime(), disposedCount, _expiredHandlers.Count); } finally { Monitor.Exit(_cleanupActiveLock); } // We didn't totally empty the cleanup queue, try again later. if (_expiredHandlers.Count > 0) { StartCleanupTimer(); } }
上述方法核心是判断是否handler对象已经被GC，如果是的话，则释放其内部资源，即网络连接。
回到最初创建HttpClient的代码，会发现并没有传入任何name参数值。这是得益于HttpClientFactoryExtensions类的扩展方法。
public static HttpClient CreateClient(this IHttpClientFactory factory) { if (factory == null) { throw new ArgumentNullException(nameof(factory)); } return factory.CreateClient(Options.DefaultName); }
Options.DefaultName的值为string.Empty。
DefaultHttpClientFactory缺少无参数的构造方法，唯一的构造方法需要传入多个参数，这也意味着构建它时需要依赖其它一些类，所以目前只适用于在ASP.NET程序中使用，还无法应用到诸如控制台一类的程序，希望之后官方能够对其继续增强，使得应用范围变得更广。
public DefaultHttpClientFactory( IServiceProvider services, ILoggerFactory loggerFactory, IOptionsMonitor<HttpClientFactoryOptions> optionsMonitor, IEnumerable<IHttpMessageHandlerBuilderFilter> filters)
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