Performance diagnostics: Adds static timer and caches handler name

Microsoft.Azure.Cosmos/src/Diagnostics/CosmosDiagnosticScope.cs

@@ -14,37 +14,44 @@ namespace Microsoft.Azure.Cosmos.Diagnostics
     /// </summary>
     internal sealed class CosmosDiagnosticScope : CosmosDiagnosticsInternal, IDisposable
     {
-        private readonly Stopwatch ElapsedTimeStopWatch;
+        private static readonly Stopwatch SingletonTimer = Stopwatch.StartNew();
+        private readonly TimeSpan startTimeSpan = CosmosDiagnosticScope.SingletonTimer.Elapsed;
+        private TimeSpan? elapsedTimeSpan = null;
+
         private bool isDisposed = false;
 
         public CosmosDiagnosticScope(
             string name)
         {
             this.Id = name;
-            this.ElapsedTimeStopWatch = Stopwatch.StartNew();
         }
 
         public string Id { get; }
 
         public bool TryGetElapsedTime(out TimeSpan elapsedTime)
         {
-            if (!this.isDisposed)
+            if (!this.isDisposed || !this.elapsedTimeSpan.HasValue)
             {
                 return false;
             }
 
-            elapsedTime = this.ElapsedTimeStopWatch.Elapsed;
+            elapsedTime = this.elapsedTimeSpan.Value;
             return true;
         }
 
         internal TimeSpan GetElapsedTime()
         {
-            return this.ElapsedTimeStopWatch.Elapsed;
+            if (this.elapsedTimeSpan.HasValue)
+            {
+                return this.elapsedTimeSpan.Value;
+            }
+
+            return CosmosDiagnosticScope.SingletonTimer.Elapsed - this.startTimeSpan;
         }
 
         internal bool IsComplete()
         {
-            return !this.ElapsedTimeStopWatch.IsRunning;
+            return this.elapsedTimeSpan.HasValue;
         }
 
         public void Dispose()
@@ -54,7 +61,7 @@ public void Dispose()
                 return;
             }
 
-            this.ElapsedTimeStopWatch.Stop();
+            this.elapsedTimeSpan = CosmosDiagnosticScope.SingletonTimer.Elapsed - this.startTimeSpan;
             this.isDisposed = true;
         }
 

Microsoft.Azure.Cosmos/src/Diagnostics/RequestHandlerScope.cs

@@ -9,7 +9,10 @@ namespace Microsoft.Azure.Cosmos.Diagnostics
 
     internal sealed class RequestHandlerScope : CosmosDiagnosticsInternal, IDisposable
     {
-        private readonly Stopwatch ElapsedTimeStopWatch;
+        private static readonly Stopwatch SingletonTimer = Stopwatch.StartNew();
+        private readonly TimeSpan startTimeSpan = RequestHandlerScope.SingletonTimer.Elapsed;
+        private TimeSpan? elapsedTimeSpan = null;
+
         private bool isDisposed = false;
 
         public RequestHandlerScope(RequestHandler handler)
@@ -19,31 +22,30 @@ public RequestHandlerScope(RequestHandler handler)
                 throw new ArgumentNullException(nameof(handler));
             }
 
-            this.Id = handler.GetType().FullName;
-            this.ElapsedTimeStopWatch = Stopwatch.StartNew();
+            this.Id = handler.FullHandlerName;
         }
 
         public string Id { get; }
 
         public bool TryGetTotalElapsedTime(out TimeSpan elapsedTime)
         {
-            if (!this.isDisposed)
+            if (!this.isDisposed || !this.elapsedTimeSpan.HasValue)
             {
                 return false;
             }
 
-            elapsedTime = this.ElapsedTimeStopWatch.Elapsed;
+            elapsedTime = this.elapsedTimeSpan.Value;
             return true;
         }
 
         internal TimeSpan GetCurrentElapsedTime()
         {
-            return this.ElapsedTimeStopWatch.Elapsed;
+            return RequestHandlerScope.SingletonTimer.Elapsed - this.startTimeSpan;
         }
 
         internal bool IsComplete()
         {
-            return !this.ElapsedTimeStopWatch.IsRunning;
+            return this.elapsedTimeSpan.HasValue;
         }
 
         public void Dispose()
@@ -53,7 +55,7 @@ public void Dispose()
                 return;
             }
 
-            this.ElapsedTimeStopWatch.Stop();
+            this.elapsedTimeSpan = RequestHandlerScope.SingletonTimer.Elapsed - this.startTimeSpan;
             this.isDisposed = true;
         }
 

Microsoft.Azure.Cosmos/src/Handler/RequestHandler.cs

@@ -16,11 +16,21 @@ namespace Microsoft.Azure.Cosmos
     /// </remarks>
     public abstract class RequestHandler
     {
+        internal readonly string FullHandlerName;
+
         /// <summary>
         /// Defines a next handler to be called in the chain.
         /// </summary>
         public RequestHandler InnerHandler { get; set; }
 
+        /// <summary>
+        /// The default constructor for the RequestHandler
+        /// </summary>
+        public RequestHandler()
+        {
+            this.FullHandlerName = this.GetType().FullName;
+        }
+
         /// <summary>
         /// Processes the current <see cref="RequestMessage"/> in the current handler and sends the current <see cref="RequestMessage"/> to the next handler in the chain.
         /// </summary>

Microsoft.Azure.Cosmos/src/Handler/RouterHandler.cs

@@ -20,37 +20,18 @@ public RouterHandler(
             RequestHandler documentFeedHandler,
             RequestHandler pointOperationHandler)
         {
-            if (documentFeedHandler == null)
-            {
-                throw new ArgumentNullException(nameof(documentFeedHandler));
-            }
-
-            if (pointOperationHandler == null)
-            {
-                throw new ArgumentNullException(nameof(pointOperationHandler));
-            }
-
-            this.documentFeedHandler = documentFeedHandler;
-            this.pointOperationHandler = pointOperationHandler;
+            this.documentFeedHandler = documentFeedHandler ?? throw new ArgumentNullException(nameof(documentFeedHandler));
+            this.pointOperationHandler = pointOperationHandler ?? throw new ArgumentNullException(nameof(pointOperationHandler));
         }
 
-        public override Task<ResponseMessage> SendAsync(
+        public override async Task<ResponseMessage> SendAsync(
             RequestMessage request,
             CancellationToken cancellationToken)
         {
-            RequestHandler targetHandler = null;
-            if (request.IsPartitionKeyRangeHandlerRequired)
-            {
-                targetHandler = this.documentFeedHandler;
-            }
-            else
-            {
-                targetHandler = this.pointOperationHandler;
-            }
-
+            RequestHandler targetHandler = request.IsPartitionKeyRangeHandlerRequired ? this.documentFeedHandler : this.pointOperationHandler;
             using (request.DiagnosticsContext.CreateRequestHandlerScopeScope(targetHandler))
             {
-                return targetHandler.SendAsync(request, cancellationToken);
+                return await targetHandler.SendAsync(request, cancellationToken);
             }
         }
     }

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/Contracts/DotNetSDKAPI.json

@@ -4829,6 +4829,11 @@
           ],
           "MethodInfo": "System.Threading.Tasks.Task`1[Microsoft.Azure.Cosmos.ResponseMessage] SendAsync(Microsoft.Azure.Cosmos.RequestMessage, System.Threading.CancellationToken);IsAbstract:False;IsStatic:False;IsVirtual:True;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
         },
+        "Void .ctor()": {
+          "Type": "Constructor",
+          "Attributes": [],
+          "MethodInfo": "[Void .ctor(), Void .ctor()]"
+        },
         "Void set_InnerHandler(Microsoft.Azure.Cosmos.RequestHandler)[System.Runtime.CompilerServices.CompilerGeneratedAttribute()]": {
           "Type": "Method",
           "Attributes": [