Running multiple instances of a Batch file in windows simultaneously? - windows

Question

I have a windows batch file that is invoked by windows scheduler. When I try to have multiple windows scheduler tasks trying to run the batch file simultaneously, the batch file is locked by the first process and the all the other instances fail.
Is there is way in Windows to run multiple instances of batch file simultaneously?
My script is a simple one all it does is:
set java_classpath
java javaClass

Answer 1

There is nothing inherent to batch file mechanics that limits the number of processes that can simultaneously run the same script. The actual batch script is not locked when it is run. In fact, it is possible to modify a batch script while it is running, though that is usually a very bad idea.
But a batch script could take any number of actions that would prevent simultaneous runs. The most obvious is if the script attempts to redirect output to a specific file (constant path and name). The output redirection establishes an exclusive lock that will prevent any other process from obtaining the same lock.
Another possibility is your script could be calling an external command or program that establishes an exclusive lock in some way.
Either way, there should be nothing to prevent multiple processes from launching the same script simultaneously. But if the script establishes an exclusive lock, then one (or more) of the instances may either crash or exit prematurely, or seem to hang, depending on how the failed lock aquisition is handled.
There really isn't any way to be more specific unless you post your actual script. But if it is a long script, then you should attempt to isolate where the problem is occurring before posting.

Answer 2

Windows 8 task scheduler has the following option (on the last, "Settings" tab):
If the task is already running, then the following rule applies:
Do not start a new instance (default)
Run a new instance in parallel
...
Probably you should change this setting. And also, I would suggest you look into http://serverfault.com and post there.

Answer 3

Did you try calling your batchfile by using %systemroot%\cmd.exe /K C:\path\batchfile.bat? With /K each time a new instance of cmd is opened, guess it is the shell not the file making you weird.

Answer 4

to people coming here from google simply looking for a way to run multiple instances of a .bat file simultaneously, a simple way would be this script:
set N=3
for /L %%i in (1,1,%N%) do (
start yourscript.bat
)