Add Mac support for library loading

source/icu.net/NativeMethods/NativeMethods.cs

@@ -57,7 +57,7 @@ static NativeMethods()
 
 		#region Dynamic method loading
 
-		#region Native methods for Linux
+		#region Native methods for Unix
 
 		private const int RTLD_NOW = 2;
 
@@ -81,7 +81,26 @@ private static string dlerror()
 			var ptr = _dlerror();
 			return Marshal.PtrToStringAnsi(ptr);
 		}
+		private const string MAC_LIBDL_NAME = "libdl.dylib";
 
+		[DllImport(MAC_LIBDL_NAME, SetLastError = true)]
+		private static extern IntPtr mac_dlopen(string file, int mode);
+
+		[DllImport(MAC_LIBDL_NAME, SetLastError = true)]
+		private static extern int mac_dlclose(IntPtr handle);
+
+		[DllImport(MAC_LIBDL_NAME, SetLastError = true)]
+		private static extern IntPtr mac_dlsym(IntPtr handle, string name);
+
+		[DllImport(MAC_LIBDL_NAME, EntryPoint = "dlerror")]
+		private static extern IntPtr _mac_dlerror();
+
+		private static string mac_dlerror()
+		{
+			// Don't free the string returned from _dlerror()!
+			var ptr = _mac_dlerror();
+			return Marshal.PtrToStringAnsi(ptr);
+		}
 		#endregion
 
 		#region Native methods for Windows
@@ -120,6 +139,7 @@ private enum LoadLibraryFlags : uint
 		private static IntPtr _IcuI18NLibHandle;
 
 		private static bool IsWindows => Platform.OperatingSystem == OperatingSystemType.Windows;
+		private static bool IsMac = Platform.OperatingSystem == OperatingSystemType.MacOSX;
 
 		private static IntPtr IcuCommonLibHandle
 		{
@@ -295,6 +315,17 @@ private static IntPtr GetIcuLibHandle(string basename, int icuVersion)
 				Trace.WriteLineIf(handle == IntPtr.Zero && lastError != 0,
 					$"Unable to load [{libPath}]. Error: {new Win32Exception(lastError).Message}");
 			}
+			if (IsMac)
+			{
+				var libName = $"lib{basename}.{icuVersion}.dylib";
+				libPath = string.IsNullOrEmpty(_IcuPath) ? libName : Path.Combine(_IcuPath, libName);
+
+				handle = mac_dlopen(libPath, RTLD_NOW);
+				lastError = Marshal.GetLastWin32Error();
+
+				Trace.WriteLineIf(handle == IntPtr.Zero && lastError != 0,
+					$"Unable to load [{libPath}]. Error: {lastError} ({dlerror()})");
+			}
 			else
 			{
 				var libName = $"lib{basename}.so.{icuVersion}";
@@ -306,10 +337,11 @@ private static IntPtr GetIcuLibHandle(string basename, int icuVersion)
 				Trace.WriteLineIf(handle == IntPtr.Zero && lastError != 0,
 					$"Unable to load [{libPath}]. Error: {lastError} ({dlerror()})");
 			}
+
 			if (handle == IntPtr.Zero)
 			{
 				Trace.TraceWarning("{0} of {1} failed with error {2}",
-					IsWindows ? "LoadLibraryEx" : "dlopen",
+					IsWindows ? "LoadLibraryEx" : IsMac ? "mac_dlopen" : "dlopen",
 					libPath, lastError);
 				return GetIcuLibHandle(basename, icuVersion - 1);
 			}
@@ -339,6 +371,13 @@ public static void Cleanup()
 					if (_IcuI18NLibHandle != IntPtr.Zero)
 						FreeLibrary(_IcuI18NLibHandle);
 				}
+				else if (IsMac)
+				{
+					if (_IcuCommonLibHandle != IntPtr.Zero)
+						mac_dlclose(_IcuCommonLibHandle);
+					if (_IcuI18NLibHandle != IntPtr.Zero)
+						mac_dlclose(_IcuI18NLibHandle);
+				}
 				else
 				{
 					if (_IcuCommonLibHandle != IntPtr.Zero)
@@ -389,14 +428,14 @@ private static T GetMethod<T>(IntPtr handle, string methodName, bool missingInMi
 			var versionedMethodName = $"{methodName}_{IcuVersion}";
 			var methodPointer = IsWindows ?
 				GetProcAddress(handle, versionedMethodName) :
-				dlsym(handle, versionedMethodName);
+				IsMac ? mac_dlsym(handle, versionedMethodName) : dlsym(handle, versionedMethodName);
 
 			// Some systems (eg. Tizen) don't use methods with IcuVersion suffix
 			if (methodPointer == IntPtr.Zero)
 			{
 				methodPointer = IsWindows ?
 				GetProcAddress(handle, methodName) :
-				dlsym(handle, methodName);
+				IsMac ? mac_dlsym(handle, methodName) : dlsym(handle, methodName);
 			}
 			if (methodPointer != IntPtr.Zero)
 			{