UBB.Developers Forums Community Development Programming PHP and Server-side Scripting locking a file

hi

id love to know a basic command to lock a file while the script is writing to it... nothing fancy.... and some explanation on that perhaps O_o? tks alot.

Are you going to be operating on Windows or on Unix?

If your on unix or windows nt/2000 use flock.

use Fcntl ':flock';
#lock
flock(FILE,LOCK_EX);

#unlock
flock(FILE,LOCK_UN);

No need to unlock. Perl will automatically release the lock on the file when the close command is encountered (or when the program ends)

--mark

ok, don't unlock.

thanks alot.

just a detail, is the locking done before or after the file is open?

After.

And one limitation of flock: If you open a file with mode '>' or '+>', the file gets clobbered immediately (before the lock is acquired), which can be a problem if someone else is reading from the file.

what if i create a separete file and then rename/ovewrite it over the old one? will it wait untill the last user stops reading it?

I don't understand your question.

File locking is a complex issue. If you can explain exactly how this file is being used, I'll try to suggest a locking strategy.

im making a script thatll open forums.cgi, read it, make changes and then save it..

In that case, you should use the same locking mechanism that the UBB uses.

If you really mean 'forums.cgi', rather than 'var_forums.cgi', that means you using UBB version 5x, which doesn't use flock, so you wouldn't want to use flock either. (flock is an 'advisory' lock - it only works if everybody who accesses the same file uses it.)

In UBB 5x, locking is done using the subs Lock and Unlock in ubb_library.pl. You can search for &Lock("lock.file") to see how it's used.

ok dave, thanks.

how the sub is getting the file name to lock?

local ($lockname) = shift;

?
what is shift?

shift shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down.

just call

&Lock("lock.file");

and then

&Unlock("unlock.file");

when your done.

thanks mastermind. thats a rather scaring code hehe

sorry about my bad english, will the shift delete the first 'variable' from the array (0)?

it shortens the array by one, therefor moving everything down.

*studying* ok, tks! *studying o'reillys bible....*

@array = "hello","there";
&mysub(@array);

.
.
.
.

sub mysub {
$this = shift;
$that = shift;
}


in the sub:
$this = "there";
$that = "hello";


Experts Q: Aren't arrays passed by copy, rather than by reference? you have to callsub(*array); and access @_ to alter the original array, right?

last one then. tks.
(first one from the stack, understood..)

[ February 24, 2001: Message edited by: CopyCat ]

&Unlock("unlock.file");

should be

&Unlock("lock.file");