Allow only one installer instance

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Author: Vytautas (talk, contrib)


The best way is to use a kernel mutex. You can call the Win32 API using the System plug-in. See also CreateMutex plug-in.

You can list all mutex objects using process hacker - open process properties, handles tab: Mutant, \BaseNamedObjects\myMutex, 0xd0


You should check the return value against ERROR_ALREADY_EXISTS (183) rather than 0. CreateMutex can set other errors such as ERROR_ACCESS_DENIED which results in a false positive.

The Script

Put this code in the .onInit function:

  System::Call 'kernel32::CreateMutex(i 0, i 0, t "myMutex") ?e'
  Pop $R0
  StrCmp $R0 0 +3
    MessageBox MB_OK "The installer is already running."

'myMutex' should be replaced with a unique value (e.g. "MyCompany.MyApp" or a generate a unique GUID).

The advanced way

This code will bring the already running instance to front, instead of opening a new one. Side Note (Jamyn): Strangely, if the user has first minimized the installer, and then tries to launch another copy, the following code will correctly set the first installer as the active window, but it won't "pop" it back up from being minimized. I am not sure how to do that simply, but that may be useful. Note (Rescator): Try something like System::Call "user32::ShowWindow(i r1, i 9) i." The 9 is the flag #SW_RESTORE see PSDK for more info on ShowWindow()

 System::Call "kernel32::CreateMutex(i 0, i 0, t '$(^Name)') i .r0 ?e"
 Pop $0
 StrCmp $0 0 launch
  StrLen $0 "$(^Name)"
  IntOp $0 $0 + 1
   FindWindow $1 '#32770' '' 0 $1
   IntCmp $1 0 +4
   System::Call "user32::GetWindowText(i r1, t .r2, i r0) i."
   StrCmp $2 "$(^Name)" 0 loop
   System::Call "user32::SetForegroundWindow(i r1) i."

Even more advanced

This uses the "advanced way" method. Unlike the function above, it will restore the window if the installer is minimized.

!define INSTALLERMUTEXNAME "$(^Name)" ; TODO: Should really use a GUID here!
Function .onInit
!define SYSTYPE_PTR i ; NSIS v2.4x
!define /ifndef SYSTYPE_PTR p ; NSIS v3.0+
System::Call 'kernel32::CreateMutex(${SYSTYPE_PTR}0, i1, t"${INSTALLERMUTEXNAME}")?e'
Pop $0
IntCmpU $0 183 0 launch launch ; ERROR_ALREADY_EXISTS
	StrLen $0 "$(^SetupCaption)"
	IntOp $0 $0 + 1 ; GetWindowText count includes \0
	StrCpy $1 "" ; Start FindWindow with NULL
		FindWindow $1 "#32770" "" "" $1
		StrCmp 0 $1 notfound
		System::Call 'user32::GetWindowText(${SYSTYPE_PTR}r1, t.r2, ir0)'
		StrCmp $2 "$(^SetupCaption)" 0 loop
		SendMessage $1 0x112 0xF120 0 /TIMEOUT=2000 ; WM_SYSCOMMAND:SC_RESTORE to restore the window if it is minimized
		System::Call "user32::SetForegroundWindow(${SYSTYPE_PTR}r1)"

See also

Check whether your application is running

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