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[REBOL] Re: Double trouble

From: sanghabum:aol at: 23-Jun-2001 17:21

> S> Can anyone suggest a Rebol method (i.e. as far as possible > S> OS-independent) way of my application detecting if there is > S> already an instance of it running on the machine? > > Just an idea: > > ; at the start of the script > if error? try [make-dir %temp-dir] [ > alert "Please close other instance first" > halt > ] > > ; rest of the script > > ; just before quitting... > delete %temp-dir > > (If Windows's TCP stack wasn't completely broken, you could have > simply opened a listen port instead...)
Hi Gabriele, Thanks for the response. You've given me a pretty good indication that I haven't overlooked an inbuilt Rebol mechanism,--- and you've replicated my original thinking (which was forget about TCP stack; try getting a write lock on a file). I thought "write lock on file" rather than "does directory exist?" as that lets me distinguish three cases: --File doesn't exist: I'm the only instance. --File does exist and I can't write to it: I'm a second instance and must close. --File does exists and I can write to it: I'm the only instance, but an earlier one fell over; so maybe I've got some cleaning up to do. However, I can't find any way of getting Rebol to place a write-lock on a file--I can happily write to the same file from two Rebol instances without getting the error response I need, e.g.: Instance 1: MyPort: open/write/direct make file! %doubleTroubleTest insert myport "blah blah" Instance 2: MyPort: open/write/direct make file! %doubleTroubleTest insert myport "blah blah" Obviously, I can write a locking mechanism based on shared areas of a common file. I can even (I think) make it air tight in race conditions. But I only want to do that if there's no magic setting in a Port (or elsewhere) that gives me a write-lock. I've had a probe around and not found anything. Does anyone know better? --Thanks, --Colin.