How can I prevent a scheduled task from running if the same task is already running?

Question

I have written a php script to check if there are any new files in a folder and, if any new files exist, upload them to a server. These files can be quite large. I want to run this script frequently-let's say every 5 min-as a scheduled task so that the files get moved to the server as soon as possible. However, once the script is already attempting to upload a file, I do not want it to be run again, as I am afraid the second instance will overwrite the file that is already being uploaded to the server.

How can I run the script as a scheduled task unless the script is already running?

Solution 1

Assuming you're just setting the task to "Repeat" in the XP "Scheduled Tasks" system, no further action on your part is needed. Scheduled Tasks won't "Repeat" a task if it's already running.

If you want to override that default, you can check the box "If the task is still running, stop it at this time" to cause the task scheduler to kill the last instance before starting a new one (though it sounds like you probably don't want that).

Solution 2

The way I have done this is to run the task from a batch file that starts once a day shortly after midnight and runs until next midnight. The advantag of this is that because it's a single script you cannot get a second instance running. I suppose a disadvantage might be that you can predict exactly how often the script runs because it would wait a set time after each run. Anyhow if you're interested my script looks like:

rem *** Get the day number. When the day number changes that signals
rem *** the script to exit.

for /f "tokens=1" %%i in ('date /t') do set THEDATE=%%i
set THEDAY=%THEDATE:~0,2%

rem *** Open the log file

echo Starting Whatever >%LOGFILE%
date /t >>%LOGFILE%
echo . >>%LOGFILE%

rem *** Start the monitoring loop

:start

rem *** Run your script

rem Run the script here

rem *** Pause for 300 seconds

sleep 300

rem *** Check the day number. If it is still the same loop back to the
rem *** start of the monitoring loop.

for /f "tokens=1" %%i in ('date /t') do set THEDATE=%%i
if %THEDATE:~0,2% == %THEDAY% goto start

JR

Solution 3

In the windows task scheduler there is a checkbox (or options) for what to do if the task is already running when the task starts again. You can set it not to start or run in parallel

Comments

[Spence]

Where is that setting in the XP task scheduler? I'm not finding any way to get the XP scheduler to execute the same task multiple times in parallel.

[Kevin Kuphal]

Vista. I noticed the windows-xp tag after I entered my answer.