fixes a locking issue and exception logging

src/Umbraco.Web/WebApi/AngularJsonMediaTypeFormatter.cs

@@ -7,6 +7,7 @@ using System.Net.Http;
 using System.Net.Http.Formatting;
 using System.Text;
 using System.Threading.Tasks;
+using Umbraco.Core.Logging;
 
 namespace Umbraco.Web.WebApi
 {
@@ -32,8 +33,16 @@ namespace Umbraco.Web.WebApi
             
             using (var memStream = new MemoryStream())
             {
-                //Let the base class do all the processing using our custom stream
-                await base.WriteToStreamAsync(type, value, memStream, content, transportContext);
+                try
+                {
+                    //Let the base class do all the processing using our custom stream
+                    await base.WriteToStreamAsync(type, value, memStream, content, transportContext);
+                }
+                catch (Exception ex)
+                {
+                    LogHelper.Error<AngularJsonMediaTypeFormatter>("An error occurred writing to the output stream", ex);
+                    throw;
+                }
 
                 memStream.Flush();
                 memStream.Position = 0;

src/umbraco.cms/businesslogic/macro/MacroEngineFactory.cs

@@ -28,11 +28,13 @@ namespace umbraco.cms.businesslogic.macro
 
 		internal static void EnsureInitialize()
 		{
-			if (_isInitialized)
-				return;
-
-			using (new WriteLock(Lock))
+			using (var lck = new UpgradeableReadLock(Lock))
 			{
+                if (_isInitialized)
+                    return;
+
+                lck.UpgradeToWriteLock();
+
 				AllEngines.Clear();
 
 				AllEngines.AddRange(