On Wednesday April 25 2007 6:14 am, Varjü Tamás wrote: > Hello everyone! > > I have written a perl script which opens a file for reading and writing. > I tested what happens if the script is run in multiple instances by the > webserver. I put a sleep command between seeking writing position in > the file and actual writing. I filled the web form in two different > tabs of my browser and sent it. > > My impression was that the following happens: > - first instance opens the file, > - first instance seeks the writing position, > - first instance goes sleeping, > - second instance opens the same file, > - second instance seeks the writing position (different from the above > one), > - second instance goes sleeping, > - first instance wakes up, > - first instance writes the file, > - first instance closes the file, > - second instance wakes up, > - second instance writes the file, > - second instance closes the file. > > After that procedure both changes has appeared in the file. > > Does it mean, that on this system the multiple instance writing of a > file is handled well and I do not have to worry about locking the file > as long as the different instances write different positions in the > file? Even the system administrator had the tip, that only the last > change will appear. > > If I want to be sure that multiple instance writing will work, is append > a better choice? I have read that on the archive of this list. > > Thanks
you should use flock to lock the file , so one process can work on it at a time , if you don't eventually a race way condition will occur and you will see a lock up happen , or if your luck one process will overwrite the other and you will just loose data.. either way it's just smart programming to lock a file your working on especially if it's happening under CGI conditions. Greg -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
