Hi Michal,
Did I understand correctly, that RENAME is not an atomic operation for
network drives?
Regards
Ladislav
> Hi,
>
> the problem was discussed here some time before. You need some atomic
> operation, which cannot be successfully done by two processes at the
> same time. One such operation is in most OSes (including Windows NT)
> local file rename. Any operation on network drives (NetBios or NFS) is
> not atomic, so you cannot rely on it when synchronizing multiple PCs -
> file locking suggested by Brett Handley is reliable only with a local
> file, not a file on a network disk.
>
> I think that you should use TCP port on the server as suggested by
> Brett Handley. There are also several distributed mutual exclusion
> algorithms that don't require a central server, look at this paper for
> more information:
> http://www.cse.iitk.ac.in/~deepak/cs632/mutual-exclusion.ps
>
> HTH,
>
> --
> Michal Kracik
>
> "CRS - Psy Sel/SPO, COUSSEMENT Christophe, CPN" wrote:
> >
> > Hi REBOLians:
> >
> > I'm confronted with a little but important problem...
> >
> > I'm using a block structure for storing data on a server.
> > 40 PC's -soon 80- could potentialy dump their data on the same time into
one
> > single data file on the server.
> > Because we using Win NT -which I do not trust for reability-, I use a
system
> > of token to insure concurrent access to the file:
> >
> > <snip>
> >
> > forever [
> > either all [(count<= 20) token?] [
> > count: count + 1
> > ;--- attempt to reserve token
> > if error? err: try [write token-file now (true)][
> > disarm err
> > return false
> > ]
> > wait 5 ;--- take delay to be sure token is written
> > ;--- try write operations
> > answers: load local-file
> > either error? err: try [save remote-file append
load
> > remote-file answers (true)][
> > ;--- release token
> > delete token-file
> > disarm err
> > return false
> > ][
> > ;--- release token
> > delete token-file
> > delete local-file
> > return true
> > ]
> >
> > ][
> > return false
> > ]
> > ]
> >
> > token?: func [][
> > return not exists? rejoin [global-answer-path global-token]
> > ]
> >
> > </snip>
> >
> > The token is just a text file in this case, and gives the PC the right
to
> > "talk" to the server.
> > The proc checks for the existence of a token on the server, for a
maximum of
> > 20 times. If there's no token on the server, it writes its own one, dump
the
> > data and release the token.
> > Empirically, I had to set a delay of 5 sec to ensure the token is
written,
> > because of the slow network connection.
> >
> > Well, my question is not about straight REBOL, but more a matter of
> > methodology :
> >
> > The procedure works, but, as you can imagine, it is not very efficient
for
> > so many PC working and dumping together.
> > How can I achieve a better performence regarding concurrent access in
REBOL
> > on WinNT, which can garanty me no data will be lost ?
> >
> > Best regard,
> >
> > chr==
> >
> > --
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> > subject, without the quotes.
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