Dial SocketsHttpHandler scavenge time based on idle timeout

Similar to netfx.

Author: stephentoub

src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs

@@ -30,12 +30,7 @@ namespace System.Net.Http
     internal sealed class HttpConnectionPoolManager : IDisposable
     {
         /// <summary>How frequently an operation should be initiated to clean out old pools and connections in those pools.</summary>
-        private const int CleanPoolTimeoutMilliseconds =
-#if DEBUG
-            1_000;
-#else
-            30_000;
-#endif
+        private readonly TimeSpan _cleanPoolTimeout;
         /// <summary>The pools, indexed by endpoint.</summary>
         private readonly ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool> _pools;
         /// <summary>Timer used to initiate cleaning of the pools.</summary>
@@ -63,7 +58,21 @@ public HttpConnectionPoolManager(HttpConnectionSettings settings)
             _settings = settings;
             _maxConnectionsPerServer = settings._maxConnectionsPerServer;
             _pools = new ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>();
+
             // Start out with the timer not running, since we have no pools.
+            // When it does run, run it with a frequency based on the idle timeout.
+            if (settings._pooledConnectionIdleTimeout == Timeout.InfiniteTimeSpan)
+            {
+                const int DefaultScavengeSeconds = 30;
+                _cleanPoolTimeout = TimeSpan.FromSeconds(DefaultScavengeSeconds);
+            }
+            else
+            {
+                const int ScavengesPerIdle = 4;
+                const int MinScavengeSeconds = 1;
+                TimeSpan timerPeriod = settings._pooledConnectionIdleTimeout / ScavengesPerIdle;
+                _cleanPoolTimeout = timerPeriod.TotalSeconds >= MinScavengeSeconds ? timerPeriod : TimeSpan.FromSeconds(MinScavengeSeconds);
+            }
 
             // Figure out proxy stuff.
             if (settings._useProxy)
@@ -194,7 +203,7 @@ public Task<HttpResponseMessage> SendAsyncCore(HttpRequestMessage request, Uri p
                     {
                         if (!_timerIsRunning)
                         {
-                            _cleaningTimer.Change(CleanPoolTimeoutMilliseconds, CleanPoolTimeoutMilliseconds);
+                            _cleaningTimer.Change(_cleanPoolTimeout, _cleanPoolTimeout);
                             _timerIsRunning = true;
                         }
                     }