Implemented C# GC get heap size/ get used size

src/coreclr/vm/mono/mono_coreclr.cpp

@@ -86,6 +86,8 @@ struct HostStruct
     gboolean (*class_is_valuetype)(MonoClass* klass);
     MonoException* (*exception_from_name_msg)(MonoImage* image, const char* name_space, const char* name, const char* msg);
     MonoReflectionField* (*field_get_object)(MonoDomain* domain, MonoClass* klass, MonoClassField* field);
+    gint64 (*gc_get_heap_size)();
+    gint64 (*gc_get_used_size)();
     intptr_t (*gchandle_get_target_v2)(intptr_t handleIn);
     uintptr_t (*gchandle_new_v2)(MonoObject* obj, gboolean pinned);
     uintptr_t (*gchandle_new_weakref_v2)(MonoObject* obj, gboolean track_resurrection);
@@ -1292,11 +1294,10 @@ extern "C" EXPORT_API int EXPORT_CC mono_gc_collect_a_little ()
     return 0;
 }
 
+// Generated by UnityEmbedHost.Generator - Commit these changes
 extern "C" EXPORT_API gint64 EXPORT_CC mono_gc_get_heap_size()
 {
-    FCALL_CONTRACT;
-    // NOT CORRECT
-    return GCHeapUtilities::GetGCHeap()->GetTotalBytesInUse();
+    return g_HostStruct->gc_get_heap_size();
 }
 
 extern "C" EXPORT_API gint64 EXPORT_CC mono_gc_get_max_time_slice_ns ()
@@ -1305,10 +1306,10 @@ extern "C" EXPORT_API gint64 EXPORT_CC mono_gc_get_max_time_slice_ns ()
     return 0;
 }
 
+// Generated by UnityEmbedHost.Generator - Commit these changes
 extern "C" EXPORT_API gint64 EXPORT_CC mono_gc_get_used_size()
 {
-    FCALL_CONTRACT;
-    return GCHeapUtilities::GetGCHeap()->GetTotalBytesInUse();
+    return g_HostStruct->gc_get_used_size();
 }
 
 extern "C" EXPORT_API gboolean EXPORT_CC mono_gc_is_incremental ()

unity/UnityEmbedHost.Tests/BaseEmbeddingApiTests.cs

@@ -783,6 +783,51 @@ public void UnityMethodIsGenericReturnsProperValue(Type objType, string methodNa
         Assert.That(isGeneric, Is.EqualTo(expectedResult));
     }
 
+    [Test]
+    [Timeout(50000)]
+    public void GcGetHeapSizeReturnsProperValue()
+    {
+        GC.Collect(0,GCCollectionMode.Forced, true);
+        GC.WaitForPendingFinalizers();
+
+        long heapSize = ClrHost.gc_get_heap_size();
+        while (heapSize == 0)
+        {
+            Thread.Sleep(0);
+            heapSize = ClrHost.gc_get_used_size();
+        }
+        Assert.NotZero(heapSize);
+        int dataSize = 1024 * 1024 * 100;
+        int[] data = new int[dataSize];
+        GC.Collect();
+        heapSize = ClrHost.gc_get_heap_size();
+        Assert.Greater(heapSize, dataSize * sizeof(int));
+        GC.KeepAlive(data);
+    }
+
+    [Test]
+    [Timeout(50000)]
+    public void GcGetUsedSizeReturnsProperValue()
+    {
+        GC.Collect(0,GCCollectionMode.Forced, true);
+        GC.WaitForPendingFinalizers();
+
+        long usedSize = ClrHost.gc_get_used_size();
+        while (usedSize == 0)
+        {
+            Thread.Sleep(0);
+            usedSize = ClrHost.gc_get_used_size();
+        }
+
+        Assert.NotZero(usedSize);
+        int dataSize = 1024 * 1024 * 100;
+        int[] data = new int[dataSize];
+        GC.Collect();
+        usedSize = ClrHost.gc_get_used_size();
+        Assert.Greater(usedSize, dataSize * sizeof(int));
+        GC.KeepAlive(data);
+    }
+
     static List<object?> FlattenedArray(Array arr)
     {
         var result = new List<object?>();

unity/unity-embed-host/CoreCLRHost.cs

@@ -616,7 +616,7 @@ public static bool unity_class_is_abstract(
         Type t = klass.TypeFromHandleIntPtr();
         return t.IsAbstract;
     }
-  
+
     private static ConcurrentDictionary<IntPtr, bool> s_isBlittableCache = new ConcurrentDictionary<IntPtr, bool>();
     [return: NativeCallbackType("gboolean")]
     public static bool class_is_blittable(
@@ -671,6 +671,21 @@ public static bool unity_mono_method_is_generic(
         return metBase.IsGenericMethodDefinition;
     }
 
+    [return: NativeCallbackType("gint64")]
+    public static long gc_get_heap_size()
+    {
+        var info = GC.GetGCMemoryInfo();
+        return info.HeapSizeBytes;
+    }
+
+    [return: NativeCallbackType("gint64")]
+    public static long gc_get_used_size()
+    {
+        var info = GC.GetGCMemoryInfo();
+        var heapSz =  info.HeapSizeBytes;
+        return heapSz - info.FragmentedBytes;
+    }
+
     static void Log(string message)
     {
         var bytes = System.Text.Encoding.UTF8.GetBytes(message);