Fix interrupting blocking file IO on Windows.

Revert part of #1131
as it causes hangs in calls to CancelSynchronousIo

Author: joncham

mono/metadata/w32file-win32.c

@@ -95,19 +95,20 @@ mono_w32file_read (gpointer handle, gpointer buffer, guint32 numbytes, guint32 *
 
 	gboolean interrupted;
 	guint32 last_error;
-	gboolean res;
+	gboolean res = FALSE;
 
-	MonoThreadInfo *info = mono_thread_info_current ();
+	mono_thread_info_install_interrupt (cancel_w32_io, handle, &interrupted);
+	if (interrupted)
+		return res;
 
-	mono_win32_enter_blocking_io_call (info, (HANDLE)handle);
 	MONO_ENTER_GC_SAFE;
 	res = ReadFile ((HANDLE)handle, buffer, numbytes, (PDWORD)bytesread, NULL);
 	/* need to save and restore since clients expect error code set for
 	 * failed IO calls and mono_thread_info_uninstall_interrupt overwrites value */
 	last_error = mono_w32error_get_last ();
 
 	MONO_EXIT_GC_SAFE;
-	mono_win32_leave_blocking_io_call (info, (HANDLE)handle);
+	mono_thread_info_uninstall_interrupt (&interrupted);
 	mono_w32error_set_last (last_error);
 
 
@@ -119,18 +120,19 @@ mono_w32file_write (gpointer handle, gconstpointer buffer, guint32 numbytes, gui
 {
 	gboolean interrupted;
 	guint32 last_error;
-	gboolean res;
+	gboolean res = FALSE;
 
-	MonoThreadInfo *info = mono_thread_info_current ();
+	mono_thread_info_install_interrupt (cancel_w32_io, handle, &interrupted);
+	if (interrupted)
+		return res;
 
-	mono_win32_enter_blocking_io_call (info, (HANDLE)handle);
 	MONO_ENTER_GC_SAFE;
 	res = WriteFile ((HANDLE)handle, buffer, numbytes, (PDWORD)byteswritten, NULL);
 	/* need to save and restore since clients expect error code set for
 	* failed IO calls and mono_thread_info_uninstall_interrupt overwrites value */
 	last_error = mono_w32error_get_last ();
 	MONO_EXIT_GC_SAFE;
-	mono_win32_leave_blocking_io_call (info, (HANDLE)handle);
+	mono_thread_info_uninstall_interrupt (&interrupted);
 	mono_w32error_set_last (last_error);
 
 	return res;

mono/utils/mono-threads-windows.c

@@ -113,7 +113,10 @@ suspend_abort_syscall (PVOID thread_info, HANDLE native_thread_handle, DWORD tid
 	// all outputstanding sync IO for target thread. If its not blocked on a sync IO request, below
 	// call will just fail and nothing will be canceled. If thread is waiting on overlapped IO,
 	// the queued APC will take care of cancel specific outstanding IO requests.
-	CancelSynchronousIo (native_thread_handle);
+
+	// UNITY: Only call CancelSynchronousIo if needed. Can cause hangs if arbitrarily called
+	if (((MonoThreadInfo*)thread_info)->win32_apc_info_io_handle != INVALID_HANDLE_VALUE)
+		CancelSynchronousIo (native_thread_handle);
 #endif
 }