Simplify and unify EnumCalendars interop (dotnet/coreclr#15762)

Windows was not allocating GCHandles, switch Unix to do the same.

Signed-off-by: dotnet-bot-corefx-mirror <dotnet-bot@microsoft.com>

Author: jkotas

src/Common/src/CoreLib/System/Globalization/CalendarData.Unix.cs

@@ -4,9 +4,9 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Runtime.InteropServices;
 using System.Security;
 using System.Text;
+using Internal.Runtime.CompilerServices;
 
 namespace System.Globalization
 {
@@ -109,9 +109,10 @@ private static bool EnumDatePatterns(string localeName, CalendarId calendarId, C
         {
             datePatterns = null;
 
-            CallbackContext callbackContext = new CallbackContext();
+            EnumCalendarsData callbackContext = new EnumCalendarsData();
+            callbackContext.Results = new List<string>();
             callbackContext.DisallowDuplicates = true;
-            bool result = EnumCalendarInfo(localeName, calendarId, dataType, callbackContext);
+            bool result = EnumCalendarInfo(localeName, calendarId, dataType, ref callbackContext);
             if (result)
             {
                 List<string> datePatternsList = callbackContext.Results;
@@ -244,8 +245,9 @@ private static bool EnumMonthNames(string localeName, CalendarId calendarId, Cal
         {
             monthNames = null;
 
-            CallbackContext callbackContext = new CallbackContext();
-            bool result = EnumCalendarInfo(localeName, calendarId, dataType, callbackContext);
+            EnumCalendarsData callbackContext = new EnumCalendarsData();
+            callbackContext.Results = new List<string>();
+            bool result = EnumCalendarInfo(localeName, calendarId, dataType, ref callbackContext);
             if (result)
             {
                 // the month-name arrays are expected to have 13 elements.  If ICU only returns 12, add an
@@ -280,8 +282,9 @@ internal static bool EnumCalendarInfo(string localeName, CalendarId calendarId,
         {
             calendarData = null;
 
-            CallbackContext callbackContext = new CallbackContext();
-            bool result = EnumCalendarInfo(localeName, calendarId, dataType, callbackContext);
+            EnumCalendarsData callbackContext = new EnumCalendarsData();
+            callbackContext.Results = new List<string>();
+            bool result = EnumCalendarInfo(localeName, calendarId, dataType, ref callbackContext);
             if (result)
             {
                 calendarData = callbackContext.Results.ToArray();
@@ -290,24 +293,16 @@ internal static bool EnumCalendarInfo(string localeName, CalendarId calendarId,
             return result;
         }
 
-        private static bool EnumCalendarInfo(string localeName, CalendarId calendarId, CalendarDataType dataType, CallbackContext callbackContext)
+        private static unsafe bool EnumCalendarInfo(string localeName, CalendarId calendarId, CalendarDataType dataType, ref EnumCalendarsData callbackContext)
         {
-            GCHandle context = GCHandle.Alloc(callbackContext);
-            try
-            {
-                return Interop.GlobalizationInterop.EnumCalendarInfo(EnumCalendarInfoCallback, localeName, calendarId, dataType, (IntPtr)context);
-            }
-            finally
-            {
-                context.Free();
-            }
+            return Interop.GlobalizationInterop.EnumCalendarInfo(EnumCalendarInfoCallback, localeName, calendarId, dataType, (IntPtr)Unsafe.AsPointer(ref callbackContext));
         }
 
-        private static void EnumCalendarInfoCallback(string calendarString, IntPtr context)
+        private static unsafe void EnumCalendarInfoCallback(string calendarString, IntPtr context)
         {
             try
             {
-                CallbackContext callbackContext = (CallbackContext)((GCHandle)context).Target;
+                ref EnumCalendarsData callbackContext = ref Unsafe.As<byte, EnumCalendarsData>(ref *(byte*)context);
 
                 if (callbackContext.DisallowDuplicates)
                 {
@@ -331,17 +326,10 @@ private static void EnumCalendarInfoCallback(string calendarString, IntPtr conte
             }
         }
 
-        private class CallbackContext
+        private struct EnumCalendarsData
         {
-            private List<string> _results = new List<string>();
-
-            public CallbackContext()
-            {
-            }
-
-            public List<string> Results { get { return _results; } }
-
-            public bool DisallowDuplicates { get; set; }
+            public List<string> Results;
+            public bool DisallowDuplicates;
         }
     }
 }

src/Common/src/CoreLib/System/Globalization/CalendarData.Windows.cs

@@ -274,7 +274,7 @@ private static unsafe bool CallGetCalendarInfoEx(string localeName, CalendarId c
         }
 
         // Context for EnumCalendarInfoExEx callback.
-        private class EnumData
+        private struct EnumData
         {
             public string userOverride;
             public List<string> strings;
@@ -427,7 +427,7 @@ private static bool GetCalendarMonthInfo(string localeName, CalendarId calendar,
         //
         // struct to help our calendar data enumaration callback
         //
-        private class EnumCalendarsData
+        private struct EnumCalendarsData
         {
             public int userOverride;   // user override value (if found)
             public List<int> calendars;      // list of calendars found so far