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While looking into communication between processes, I wrote the routine SetMutex()
which is quite simple but very effective, and I thought it is worth sharing ...
The routine can be used to signal the execution of a command, routine or process
which then may be monitored by any other process.
The demo program lets you create and monitor lots of named Mutexes.
At start it launches a second instances but additional ones can be loaded at any time.
Keep in mind that a Mutex can only be destroyed in the program where it was created
- by CloseHandle() or by terminating the program.
In this demo the BackSpace key closes only the last handle that was created locally.
The demo has been compiled under PB/CC 5.01. I would assume that it works with PB/Win,
if the #CONSOLE OFF is left out.
Gert Voland.
Attached are .bas and .exe.
which is quite simple but very effective, and I thought it is worth sharing ...
The routine can be used to signal the execution of a command, routine or process
which then may be monitored by any other process.
The demo program lets you create and monitor lots of named Mutexes.
At start it launches a second instances but additional ones can be loaded at any time.
Keep in mind that a Mutex can only be destroyed in the program where it was created
- by CloseHandle() or by terminating the program.
In this demo the BackSpace key closes only the last handle that was created locally.
The demo has been compiled under PB/CC 5.01. I would assume that it works with PB/Win,
if the #CONSOLE OFF is left out.
Gert Voland.
Code:
' SetMutex.bas
' Compiler: PBCC 5.01
' OS: Windows XP
' Author: Gert Voland
' Date: 20. Apr. 2009
#COMPILE EXE "SetMutex_Test.exe"
#DIM ALL
#CONSOLE OFF
#INCLUDE "Win32Api.inc"
$ProgName = "SetMutex_Test.exe"
'---------------------------------------------------------------
FUNCTION PBMAIN () AS LONG
LOCAL x$, y$, lasty$, txt$
LOCAL ret, last AS LONG
LOCAL hGW, hDC AS DWORD
LOCAL hFont AS LONG
LOCAL i, ist AS LONG
LOCAL pID AS DWORD
' Use it here for flagging this test program
IF SetMutex($ProgName, 0) = 0 THEN ' Check
' It does not exist yet -> create it
SetMutex($ProgName, 1) ' Create
txt$ = "First instance of " + $ProgName
pID = SHELL($ProgName, 1) ' Start two more instances of this program
ELSE
' It is already loaded
txt$ = "Another instance of " + $ProgName ' Note: This does not get updated when the first instance terminates
END IF
IF pID > 0 THEN
GRAPHIC WINDOW txt$, 10, 10, 280, 500 TO hGW
ELSE
GRAPHIC WINDOW txt$, 310, 10, 280, 500 TO hGW
END IF
GRAPHIC ATTACH hGW, 0, REDRAW
FONT NEW "Courier New", 9 TO hFont
GRAPHIC SET FONT hFont
' Use it here to create, check and destroy more Mutexes
DO
GRAPHIC GET DC TO hDC
IF hDC = 0 THEN EXIT LOOP ' In case GW has been closed externally
SLEEP 0 ' Allow some CPU to other processes
GRAPHIC CLEAR ' Always start at top
GRAPHIC PRINT " Press the following keys for testing:
GRAPHIC PRINT
GRAPHIC PRINT " Create: A - Z Destroy: BS Quit: Esc"
GRAPHIC INSTAT TO ist
IF ISTRUE ist THEN
GRAPHIC INKEY$ TO x$
x$ = UCASE$(x$)
ELSE
x$ = ""
END IF
SELECT CASE x$
CASE "A" TO "Z"
y$ = "Mutex_" + x$
ret = SetMutex(y$, 1) ' Create Mutex
IF ret > 0 THEN
last = ret ' Mutex did not exist yet - it is the last one being created
lasty$ = y$ ' Remember the last one
END IF
CASE $BS ' Only close the handle created last!
IF last > 0 THEN
CloseHandle(last)
last = 0 ' Forget the last one
lasty$ = ""
END IF
CASE $ESC
EXIT LOOP
END SELECT
GRAPHIC PRINT
FOR i = ASC("A") TO ASC("Z")
y$ = "Mutex_" + CHR$(i)
ret = SetMutex(y$) ' Check Mutex
GRAPHIC PRINT " "; y$; " ";
SELECT CASE ret
CASE 0
GRAPHIC PRINT "---"
CASE -1
IF y$ = lasty$ THEN
GRAPHIC PRINT "last handle created :"; USING$(" ####", last)
ELSE
GRAPHIC PRINT "exists"
END IF
END SELECT
NEXT i
GRAPHIC REDRAW
LOOP
GRAPHIC WINDOW END
END FUNCTION
'---------------------------------------------------------------
FUNCTION SetMutex(BYVAL szMutexName AS ASCIIZ * 64, OPT BYVAL createMx AS LONG) AS LONG
' #INCLUDE "Win32API.inc" ' needed
'
' Purpose: Test if a command/routine/program has been activated by means of a named Mutex.
'
' Usage:
' (1) The first call of SetMutex("MutexName", 1) creates a Mutex and returns the create-handle.
' It may be kept for possibly using CloseHandle() later.
'
' (2) When a Mutex is checked (in whichever program) by SetMutex("MutexName", 0) an OpenMutex is executed.
' The open-handle gets closed again. Thus, the creating program is the only one to keep the Mutex handle.
' Almost any type of activity can be monitored this way, e.g. if a program is loaded,
' or if part of a program is active (or done), etc.
'
' (3) Optionally one can destroy the Mutex using CloseHandle(create-handle) in the program where it was created.
' Still, when the creating program terminates, the Mutex object gets destroyed in any case.
'
' (4) Limitation: A non-creating program cannot find out which program created the Mutex.
' For that, more inter-process communication is needed.
'
' Input: szMutexName : Name of the Mutex to be created or checked (here limited to 63 characters)
' createMx (optional) : 1 => Create the Mutex, 0 => Check the Mutex
'
' Output: FUNCTION = 0 : Mutex does not exist
' = > 0 : = Handle hMutex after creating Mutex
' = -1 : Mutex exists
LOCAL hMutex AS LONG ' Create-handle of Mutex
IF createMx = 0 THEN
' Check existence. Do not create a new handle, though.
hMutex = OpenMutex(BYVAL %MUTEX_ALL_ACCESS, BYVAL 0, szMutexName)
IF hMutex = 0 THEN
' No need to close a handle; there is none.
FUNCTION = 0 ' Mutex does not exist
ELSE
' Close the open-handle
CloseHandle(hMutex)
FUNCTION = -1 ' Mutex exists
END IF
ELSE
' Create a Mutex
hMutex = CreateMutex(BYVAL 0, BYVAL 1, szMutexName)
IF GetLastError = %ERROR_ALREADY_EXISTS THEN
' Close this handle in order to keep only the first create-handle
CloseHandle hMutex
FUNCTION = -1 ' Mutex exists
ELSE
' Do not close the create-handle. The calling program is the only one to "keep" the handle
FUNCTION = hMutex ' Return the Mutex create-handle
END IF
END IF
END FUNCTION ' SetMutex
'---------------------------------------------------------------
Attached are .bas and .exe.