base/win/wrapped_window_proc.h

// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Provides a way to handle exceptions that happen while a WindowProc is
// running. The behavior of exceptions generated inside a WindowProc is OS
// dependent, but it is possible that the OS just ignores the exception and
// continues execution, which leads to unpredictable behavior for Chrome.

#ifndef BASE_WIN_WRAPPED_WINDOW_PROC_H_
#define BASE_WIN_WRAPPED_WINDOW_PROC_H_
#pragma once

#include <windows.h>

#include "base/base_api.h"

namespace base {
namespace win {

// An exception filter for a WindowProc. The return value determines how the
// exception should be handled, following standard SEH rules. However, the
// expected behavior for this function is to not return, instead of returning
// EXCEPTION_EXECUTE_HANDLER or similar, given that in general we are not
// prepared to handle exceptions.
typedef int (__cdecl *WinProcExceptionFilter)(EXCEPTION_POINTERS* info);

// Sets the filter to deal with exceptions inside a WindowProc. Returns the old
// exception filter, if any.
// This function should be called before any window is created.
BASE_API WinProcExceptionFilter SetWinProcExceptionFilter(
    WinProcExceptionFilter filter);

// Calls the registered exception filter.
BASE_API int CallExceptionFilter(EXCEPTION_POINTERS* info);

// Wrapper that supplies a standard exception frame for the provided WindowProc.
// The normal usage is something like this:
//
// LRESULT CALLBACK MyWinProc(HWND hwnd, UINT message,
//                            WPARAM wparam, LPARAM lparam) {
//   // Do Something.
// }
//
// ...
//
//   WNDCLASSEX wc = {0};
//   wc.lpfnWndProc = WrappedWindowProc<MyWinProc>;
//   wc.lpszClassName = class_name;
//   ...
//   RegisterClassEx(&wc);
//
//   CreateWindowW(class_name, window_name, ...
//
template <WNDPROC proc>
LRESULT CALLBACK WrappedWindowProc(HWND hwnd, UINT message,
                                   WPARAM wparam, LPARAM lparam) {
  LRESULT rv = 0;
  __try {
    rv = proc(hwnd, message, wparam, lparam);
  } __except(CallExceptionFilter(GetExceptionInformation())) {
  }
  return rv;
}

}  // namespace win
}  // namespace base

#endif  // BASE_WIN_WRAPPED_WINDOW_PROC_H_