How can I prevent to run same batch file twice to allow only one instance?

Question

I need to detect if a batch file is already running or not.

In the batch I simply loop and repeatedly do some tasks. Sometimes the loop cannot complete. I run the batch file at a scheduled time. When it runs, it should check if a previous instance exists and is healthy. If it doesn't exist it should start a new instance. If the instance that exist is not healthy/outdated, the new instance should kill/cancel the older process.

A few theories:

1. How can I detect a previous instance in a batch file? Can I give an ID like thing?
2. I can use a pulse mechanism to say the batch is healty; ie, a global variable, a newly created dummy file, a timestamp in a dummy file, etc.
3. Can I detect a kind of "timeout", if the last pulse is expired then allow a new instance...

Yes, I all want them in a batch file - instead of a Windows app - I think it's not so hard for one who is a batch-file addict and takes this question as challenge!

Answer 1

This is rather difficult from a batch file standpoint, mainly because there is no guaranteed method for a batchfile to detect instances across processes.

IMO, I think you are using the wrong tool. While, yes, it is a challenge, the more important concern is "Does it work?"

I run batch file in a scheduled time.

This tells me you should be using a scheduling program, like Task Scheduler. Task Scheduler will guarantee there is only one instance of your file, even if it is running on another user.

For example, if you run the task every 30 minutes, you configure the task to run for a duration of 30 minutes. Then you set the "if task is already running" setting to "do not create a new instance." Or you have to option of "kill the old one", "Run another instance", or "Start a new task as soon as the old one is done".

For Vista and up: http://technet.microsoft.com/en-us/library/cc748993.aspx#BKMK_cmd
For Xp and up: http://technet.microsoft.com/en-us/library/bb490996.aspx

The challenging method is to create states.

1. Your batch file enters execution
2. Your batch file loops
3. Your batch file ends

You can create an arbitrary file in %allusersprofile%, like >>Startmybatchfile.txt echo 1 for each state, then check if it exists. It will also help with trouble shooting. But don't delete the file at the end. Just change it to End State. That way it's deterministic if your batch file has truly finished and no longer running.

I would not use a global variable as it requires admin privileges to run.

You could also use the %temp% variable as but that changes from user to user. I guess that isn't a concern if you are a single login user machine.

Answer 2

I just finished the batch file which one ensures both monitoring itself -the batch file- and the job file -facerecog.exe- are running smoothly. I've used hello.exe as a test probe tool, you may replace your own; ie. ping.exe, etc. When it starts without any parameter it fires another instance and quit, so you can run it as a scheduled task in specific intervals. I hope it helps someone who don't want to use advanced tools.

    @goto code

    :comments
    @REM RunMagick for FaceRecog
    @REM Runs FaceRecog forever
    @REM Author Emin Akbulut eminakbulut@gmail.com
    @REM 29/11/2011
    @REM This code is freeware


    :code
    @C:
    @CD C:\NET\FaceRecog

    :settings
    set jobexe=FaceRecog.exe
    set remotehost=192.168.35.211
    set remoteport=1333
    @REM Timeout for response of the batch, in seconds
    set /a timeout=120
    set batchtitle=Monitoring FaceRecog...


    :requirements
    @if NOT exist "stopwatch.exe" (
    @echo. stopwatch.exe is missing!
    @ping localhost > nul
    start http://www.jfitz.com/dos/stopwatch10.zip
    goto end
    ) 




    :menu
    @if "%1" == "/monitor" goto monitor
    @if "%1" == "/stop" goto request-stop
    @if "%1" == "/force-stop" goto stop


    :batch-instance-check 
    tasklist /v /fi "IMAGENAME eq cmd.exe" | find /I /c "%batchtitle%"
    @if "%ERRORLEVEL%" == "0" goto batch-instance-found
    goto start

    :batch-instance-found
    @REM Check the previous instance is healthy/responsive or not
    stopwatch stop < pulse.log > elapsed.log
    set /a elapsed=999
    for /F %%a in ('type elapsed.log') do set /a elapsed=%%a
    if %elapsed% gtr %timeout% (
    taskkill /F /FI "WINDOWTITLE eq %batchtitle%*"
    goto start
    ) else (
    @echo Already running...
    @ping localhost > nul
    goto end
    )

    del elapsed.log



    @goto monitor



    :run-job
    @REM Test FaceRecog process
    tasklist | Find "FaceRecog.exe"
    @If Not ErrorLevel 1 Goto monitor

    taskkill /f /im:conime.exe
    @PING 1.1.1.1 -n 1 -w 1000 >NUL
    start FaceRecog.exe
    @REM Take a breathe
    @PING 1.1.1.1 -n 1 -w 1000 >NUL
    @goto run-job

    :start
    @REM Fire another instance with /monitor command and exit
    start "%batchtitle%" /low /I %0 /monitor
    goto end

    :stop
    @REM Stop the job
    taskkill /F /IM:%jobexe%
    @REM Stop the batch
    taskkill /F /FI "WINDOWSTITLE eq %batchtitle%*"
    del stop.log > nul
    title Done
    goto end

    :request-stop
    @REM Ask programs to quit
    @REM %jobexe% /quit
    @REM Take a breathe
    @ping localhost > nul
    stopwatch start > stop.log
    goto end

    :monitor
    stopwatch start > pulse.log
    @REM Test /stop requested
    @if exist stop.log goto stop
    @REM Test FaceRecog process
    tasklist | Find "%jobexe%"
    @If Not ErrorLevel 0 Goto run-job

    :shorttest
    @Echo Shorttest...
    hello.exe %remotehost% %remoteport% | Find "Version" 
    @If Not ErrorLevel 1 Goto job-ok

    :crashcheck
    @REM No response, crashed?
    tasklist | Find "WerFault.exe"
    @If ErrorLevel 1 Goto longcheck
    taskkill /F /IM:WerFault.exe
    @goto shorttest

    :longcheck
    @Echo Longtest...
    @REM Last check, maybe FaceRecog was busy
    hello.exe %remotehost% %remoteport% | Find "Version" 
    @If Not ErrorLevel 1 Goto job-ok

    :nonresponsive
    @REM Kill non-responsive FaceRecog process and wait for a while to auto-revive
    taskkill /F /IM:%jobexe%



    :job-ok
    @echo OK
    @REM 10 seconds to wait then loop again
    @PING 1.1.1.1 -n 1 -w 10000 >NUL
    @goto monitor


    :end

Thanks stijn for his great comment. Thanks surfasb for his warning about Scheduled Task that already running.