don't try to use AppDomain's Monitoring in Mono since it's not implem…

…ented there

src/BenchmarkDotNet.Core/Diagnosers/MemoryDiagnoser.cs

@@ -7,6 +7,7 @@
 using BenchmarkDotNet.Running;
 using System.Linq;
 using BenchmarkDotNet.Engines;
+using BenchmarkDotNet.Portability;
 
 namespace BenchmarkDotNet.Diagnosers
 {
@@ -55,6 +56,9 @@ public AllocationColumn(Dictionary<Benchmark, GcStats> results)
             public string GetValue(Summary summary, Benchmark benchmark)
             {
 #if !CORE
+                if (RuntimeInformation.IsMono())
+                    return "?";
+
                 if (results.ContainsKey(benchmark))
                 {
                     var result = results[benchmark];

src/BenchmarkDotNet.Core/Engines/Engine.cs

@@ -3,6 +3,7 @@
 using BenchmarkDotNet.Characteristics;
 using BenchmarkDotNet.Horology;
 using BenchmarkDotNet.Jobs;
+using BenchmarkDotNet.Portability;
 using BenchmarkDotNet.Reports;
 using BenchmarkDotNet.Running;
 using JetBrains.Annotations;
@@ -172,6 +173,9 @@ private void EnableMonitoring()
             if(!IsDiagnoserAttached) // it could affect the results, we do this in separate, diagnostics-only run
                 return;
 #if CLASSIC
+            if(RuntimeInformation.IsMono()) // Monitoring is not available in Mono, see http://stackoverflow.com/questions/40234948/how-to-get-the-number-of-allocated-bytes-in-mono
+                return;
+
             AppDomain.MonitoringIsEnabled = true;
 #endif
         }

src/BenchmarkDotNet.Core/Engines/GcStats.cs

@@ -1,4 +1,5 @@
 using System;
+using BenchmarkDotNet.Portability;
 
 namespace BenchmarkDotNet.Engines
 {
@@ -79,7 +80,7 @@ private static long GetAllocatedBytes(bool isDiagnosticsEnabled)
 #if NETCOREAPP11 // when MS releases new version of .NET Runtime to nuget.org
             return GC.GetAllocatedBytesForCurrentThread(); // https://github.com/dotnet/corefx/pull/12489
 #elif CLASSIC
-            if (!isDiagnosticsEnabled)
+            if (!isDiagnosticsEnabled || RuntimeInformation.IsMono()) // Monitoring is not available in Mono, see http://stackoverflow.com/questions/40234948/how-to-get-the-number-of-allocated-bytes-
                 return 0;
 
             // "This instance Int64 property returns the number of bytes that have been allocated by a specific 

src/BenchmarkDotNet.Core/Portability/RuntimeInformation.cs

@@ -19,6 +19,8 @@ namespace BenchmarkDotNet.Portability
 {
     public class RuntimeInformation
     {
+        private static readonly bool isMono = Type.GetType("Mono.Runtime") != null; // it allocates a lot of memory, we need to check it once in order to keep Enging non-allocating!
+
         private const string Debug = "DEBUG";
         private const string Release = "RELEASE";
         internal const string Unknown = "?";
@@ -39,7 +41,7 @@ internal static bool IsWindows()
 #endif
         }
 
-        private static bool IsMono() => Type.GetType("Mono.Runtime") != null;
+        internal static bool IsMono() => isMono;
 
         internal static string GetOsVersion()
         {