Beefy Boxes and Bandwidth Generously Provided by pair Networks
go ahead... be a heretic
 
PerlMonks  

Re^2: Will these functions for use with Storable properly lock my file?

by nysus (Parson)
on Aug 04, 2021 at 01:43 UTC ( #11135600=note: print w/replies, xml ) Need Help??


in reply to Re: Will these functions for use with Storable properly lock my file?
in thread Will these functions for use with Storable properly lock my file?

_retrieve() leaks the bareword file handle LOCK, the lock file is kept locked until some other code explicitly closes that handle. _store() closes a bareword file handle never opened there.

Yes, I realize this is a litle precarious. It relies on my code always calling _retrieve() followed by _store(() at some point. It also counts on the lock getting removed when the process. Wasn't sure how else I could get around this.

If you have two instances running in parallel, and one chooses to write (calling _store()) without prior read, while the other chooses to read (calling _retrieve()), the writer will simply damage the data on disk while the reader assumes to be safe because it holds a lock. The writer doesn't even get an error, because close lacks error checks. Instant loss of data. (And trust me in that regard, Murphy will make sure that your data is damaged at the most inconvienient moment in time, causing the maximum damage.)

Yes. Bu tin my case, the processes are always upating the existing data in the file.

I tried Storable's lock functions first. They didn't work in my case (though it entirely possible I wasn't using them right. It seemed to me that something like this was happening:

1) Process A open data file to read, puts lock on it then removes lock + when done 2) Process B reads data file, puts lock on it, remove it when done. 3) Process C does the same. Now we have three different process with same data. Fine. But: 1) Process A finishes and writes to file. 2) Process D reads file. 3) Process B finishes and writes data file, overwriting A's work. 4) Process E reads file (saved by Process B). Now Process D and E have totally different starting points.

But again, maybe I was using the lock functions wrong. Not sure.

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate Priest Vicar";
$nysus = $PM . ' ' . $MCF;
Click here if you love Perl Monks

  • Comment on Re^2: Will these functions for use with Storable properly lock my file?
  • Download Code

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://11135600]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others imbibing at the Monastery: (4)
As of 2021-10-24 13:09 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My first memorable Perl project was:







    Results (89 votes). Check out past polls.

    Notices?