How to respond to WM_SettingChange inside an AutoHotKey script

Question

(This question is similar to Delphi: How to respond to WM_SettingChange/WM_WinIniChange? but for the AutoHotKey language. This is not about sending WM_SETTINGCHANGE from inside AutoHotKey.)

In another Windows process ("sender"), I change the PATH environment variable by modifying the HK_CURRENT_USER registry. Then I send/publish a WM_SETTINGCHANGE message using the SendMessageTimeout API.

My concurrently running AutoHotKey script ("receiver"), which I use as a program launcher, does not seem to be aware of the change. I want to capture this message in order to refresh the script's local copy of the PATH variable. Is it possible?

For example, the "sender" could be the System Properties dialog box, or some another AutoHotKey script:

EnvUpdate

or some other handy third-party Windows binary like nircmd:

nircmd sysrefresh environment

or some Ruby code :

### This is a -*- ruby -*- script
require 'Win32API'

module Windows::EnvByReg
  def self.envupdate()
    result = 0
    wParam_unused = 0
    timeout_ms = 5000
    SendMessageTimeout.call(HWND_BROADCAST, WM_SETTINGCHANGE,
                            wParam_unused, 'Environment',
                            SMTO_ABORTIFHUNG, timeout_ms, result)
  end
  SendMessageTimeout = Win32API.new('user32', 'SendMessageTimeout',
                                    'LLLPLLP', 'L') 
  HWND_BROADCAST = 0xffff
  WM_SETTINGCHANGE = 0x001A
  SMTO_ABORTIFHUNG = 2
end#module

if __FILE__ == $PROGRAM_NAME
   Windows::EnvByReg.envupdate
end

Answer 1

Use the OnMessage function to respond to the message.

Here is a sample script.

;;; This is an AutoHotKey -*- ahk -*- script 
;;;
;;; ABOUT
;;;  Respond to WM_SETTINGCHANGE messages and update this process's PATH
;;;  environment variable.
;;;
;;; USAGE
;;;  Run the script directly (e.g. double-click) or drag and drop onto
;;;  the AutoHotKey application.
;;;
;;; DEBUG
;;;  Optionally define a key binding to debug_show_recv_count, e.g.:
;;;    #space:: debug_show_recv_count()
;;;
;;; AUTHOR
;;;  piyo @ StackOverflow
;;;

;;
;; Register an AHK function as a callback.
;;
OnMessage( (WM_SETTINGCHANGE:=0x1A), "recv_WM_SETTINGCHANGE")

;;
;; Respond to the WM_SETTINGCHANGE message.
;;
recv_WM_SETTINGCHANGE(wParam, lParam, msg, hwnd)
{
  global g_recv_WM_SETTINGCHANGE_count
  g_recv_WM_SETTINGCHANGE_count := g_recv_WM_SETTINGCHANGE_count + 1
  ;;debug;; ToolTip Received a WM_SETTINGCHANGE !
  reset_env_path_from_registry()
}

;;
;; Import the recently changed Path environment variable from the
;; Windows Registry. Import from the System and User environments.
;;
reset_env_path_from_registry()
{
  sys_path := ""
  sys_subkey := "SYSTEM\CurrentControlSet\Control\Session Manager\Environment"
  RegRead, sys_path, HKEY_LOCAL_MACHINE, %sys_subkey%, Path
  cu_path := ""
  cu_subkey := "Environment"
  RegRead, cu_path, HKEY_CURRENT_USER, %cu_subkey%, Path
  new_path := sys_path . ";" . cu_path
  ;;debug;; MsgBox,% new_path
  EnvSet, PATH,% new_path
}

;;;

; Debug var for interactive sanity checking
g_recv_WM_SETTINGCHANGE_count := 0

; Debug function for interactive sanity checking
debug_show_recv_count() {
  global g_recv_WM_SETTINGCHANGE_count
  path := ""
  EnvGet, path, PATH
  msg := "g_recv_WM_SETTINGCHANGE := " . g_recv_WM_SETTINGCHANGE_count
  msg := msg . "!`n" . path
  MsgBox,% msg
}

;;; end