[REBOL] Re: Double trouble
From: lmecir:mbox:vol:cz at: 27-Jun-2001 17:48
Hi Pekr,
> lock: context [
>
> sem-port-spec: func [path file-name][to-file join to-string path head
change
> find copy file-name "." ".SEM"]
>
> locked: copy []
>
> get-lock: func [path file-name][
> semaphore: sem-port-spec path file-name
It looks to me, that 'semaphore will "leak" to the global context, although
you didn't intend that
> ; file doesn't exist, or does exist, but semaphore can be closed
(dead one)
> either not exists? semaphore [
> ; store pair of file-name, opened port
> append locked semaphore
> append locked open/new/direct semaphore
looks like the lock isn't exclusive, there is a possibility for two
concurrent
scripts to obtain the semaphore
> true
> ][
> ; semaphore does exist - is locked or dead one? (possible app
crash)
> either remove-sem-file semaphore [
> ; store pair of file-name, opened port
> append locked semaphore
> append locked open/new/direct semaphore
> true
> ][false] ; can't get lock, sorry ...
> ]
> ]
>
> close-lock: func [path file-name][
> semaphore: sem-port-spec path file-name
> if found? find locked semaphore [
> close select locked semaphore
> remove remove find locked semaphore
> ]
>
> either remove-sem-file semaphore [true][false]
> ]
>
> remove-sem-file: func [semaphore][either not error? try [delete
> semaphore][true][false]]
>
> ]
>
> example:
>
> lock/get-lock target-path "file-name.txt" ; will
create
> file-name.sem on 'target-path
> if not lock/get-lock [print "unable to lock file"] ; should
print
> "unable to lock file" message ...
> probe lock/locked ;
will show
> you
> lock/close-lock target-path "file-name.txt" ; will
unlock file
> ... so, the problem is, that unix will allow you to delete file even if
you would
> own regular lock. A little bit lame imo.
>
> -pekr-
>
I have got an exclusive file-based multiplatform locking mechanism, but it
is a part of a larger script and I should rewrite it as stand-alone before
it can be presented here...
