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Hi,

I know that vba isn't really written to allow this, but it's the only
tool I've got available.

My monte carlo model takes four hours to run on a single machine. I
thought it would be a good idea to split the processing over several
machines.

I've set the model up so the number of simulations is split up, and
each machine takes a set of these and runs with them (each machine
takes a 'job'). So far so good.

To allocate which machine takes which job I've written the job names
in an excel file. The machines poll on this file until it is
available. Once they get it and open it they take a job (and set a
flag to say they've taken it), close the file and run with the job.

I use the following code for the polling (isFileOpen is a function I
fonud on the MS support site - similar to John Walkenbachs
fileIsOpen()) :

***

While (IsFileOpen(wbname))
' wait a short (random) time (up to ten seconds)
waitTime = Rnd() * 10
Debug.Print Now()
Application.Wait (Now + TimeValue("0:00:" & waitTime & ""))
DoEvents
Wend

' ok open the file, take a job etc....
workbook(wbname).open ......
***

Now, I'm really concerned about concurrency issues - since three
machines could theoretically all hit the isFileOpen at the same time
and attempt to open it (or set the same flags). This would cause any
number of difficult to solve problems.

Anyone got any ideas? is there a quicker (i.e. atomic) way to check
and open a file? can anyone think of someway of using locks on the
file? Any advice from someone who's tried similar?

Many thanks,

Chris