Make prefix add & remove thread safe.

src/Microsoft.Net.Http.Server/UrlPrefixCollection.cs

@@ -23,7 +23,13 @@ namespace Microsoft.Net.Http.Server
 
         public int Count
         {
-            get { return _prefixes.Count; }
+            get
+            {
+                lock (_prefixes)
+                {
+                    return _prefixes.Count;
+                }
+            }
         }
 
         public bool IsReadOnly
@@ -37,6 +43,8 @@ namespace Microsoft.Net.Http.Server
         }
 
         public void Add(UrlPrefix item)
+        {
+            lock (_prefixes)
             {
                 var id = _nextId++;
                 if (_webListener.IsListening)
@@ -45,13 +53,19 @@ namespace Microsoft.Net.Http.Server
                 }
                 _prefixes.Add(id, item);
             }
+        }
 
         internal UrlPrefix GetPrefix(int id)
+        {
+            lock (_prefixes)
             {
                 return _prefixes[id];
             }
+        }
 
         public void Clear()
+        {
+            lock (_prefixes)
             {
                 if (_webListener.IsListening)
                 {
@@ -59,16 +73,23 @@ namespace Microsoft.Net.Http.Server
                 }
                 _prefixes.Clear();
             }
+        }
 
         public bool Contains(UrlPrefix item)
+        {
+            lock (_prefixes)
             {
                 return _prefixes.Values.Contains(item);
             }
+        }
 
         public void CopyTo(UrlPrefix[] array, int arrayIndex)
+        {
+            lock (_prefixes)
             {
                 _prefixes.Values.CopyTo(array, arrayIndex);
             }
+        }
 
         public bool Remove(string prefix)
         {
@@ -76,6 +97,8 @@ namespace Microsoft.Net.Http.Server
         }
 
         public bool Remove(UrlPrefix item)
+        {
+            lock (_prefixes)
             {
                 int? id = null;
                 foreach (var pair in _prefixes)
@@ -96,11 +119,15 @@ namespace Microsoft.Net.Http.Server
                 }
                 return false;
             }
+        }
 
         public IEnumerator<UrlPrefix> GetEnumerator()
+        {
+            lock (_prefixes)
             {
                 return _prefixes.Values.GetEnumerator();
             }
+        }
 
         IEnumerator IEnumerable.GetEnumerator()
         {
@@ -108,6 +135,8 @@ namespace Microsoft.Net.Http.Server
         }
 
         internal void RegisterAllPrefixes()
+        {
+            lock (_prefixes)
             {
                 // go through the uri list and register for each one of them
                 foreach (var pair in _prefixes)
@@ -116,8 +145,11 @@ namespace Microsoft.Net.Http.Server
                     RegisterPrefix(pair.Value.Whole, pair.Key);
                 }
             }
+        }
 
         internal void UnregisterAllPrefixes()
+        {
+            lock (_prefixes)
             {
                 // go through the uri list and unregister for each one of them
                 foreach (var prefix in _prefixes.Values)
@@ -126,6 +158,7 @@ namespace Microsoft.Net.Http.Server
                     UnregisterPrefix(prefix.Whole);
                 }
             }
+        }
 
         private void RegisterPrefix(string uriPrefix, int contextId)
         {