PHP instances writing to the same file?

[abrtlt@yahoo.com]

I read in Programming PHP (O'Reilly) that flock() "cannot prevent two
PHP scripts running in the same web server process from accessing a
file at the same time".
In my case a single PHP script appends text strings to an existing text
file. Several clients may trigger the same script on the same web page
and thus more than one PHP instance might try to open and append text
to the same file at the same time. I would assume that using flock()
_does_ in fact prevent simultaneous access in this case. Am I correct?
Thanks!

Andrew

[Henrik Hansen]

Re: PHP instances writing to the same file?

abrtlt@yahoo.co m writes:
[color=blue]
> I read in Programming PHP (O'Reilly) that flock() "cannot prevent two
> PHP scripts running in the same web server process from accessing a
> file at the same time".
> In my case a single PHP script appends text strings to an existing text
> file. Several clients may trigger the same script on the same web page
> and thus more than one PHP instance might try to open and append text
> to the same file at the same time. I would assume that using flock()
> _does_ in fact prevent simultaneous access in this case. Am I correct?[/color]

You are correct

There are different types of locks though but LOCK_EX should de what
you want..

--
Henrik Hansen

[Chung Leong]

Re: PHP instances writing to the same file?

abrtlt@yahoo.co m wrote:[color=blue]
> I read in Programming PHP (O'Reilly) that flock() "cannot prevent two
> PHP scripts running in the same web server process from accessing a
> file at the same time".
> In my case a single PHP script appends text strings to an existing text
> file. Several clients may trigger the same script on the same web page
> and thus more than one PHP instance might try to open and append text
> to the same file at the same time. I would assume that using flock()
> _does_ in fact prevent simultaneous access in this case. Am I correct?
> Thanks!
>
> Andrew[/color]

What is meant I think is that flock() does not work on multithreaded
environments like Windows, where all multiple PHP instances run inside
the same process.

[jon.tjemsland@gmail.com]

Re: PHP instances writing to the same file?

What OS is the server that this script is running on? Flock will work
to lock a file if you are running your script on a server with an OS
that is compatible with flock. Both NFS and FAT file systems are
incompatible.

Here is a flock sample from (http://us3.php.net/flock):

$fp = fopen("/tmp/lock.txt", "w+");
if (flock($fp, LOCK_EX)) { // do an exclusive lock
fwrite($fp, "Write something here\n");
flock($fp, LOCK_UN); // release the lock
} else {
echo "Couldn't lock the file !";
}
fclose($fp);


Regards

Jon Tjemsland


abrtlt@yahoo.co m wrote:[color=blue]
> I read in Programming PHP (O'Reilly) that flock() "cannot prevent two
> PHP scripts running in the same web server process from accessing a
> file at the same time".
> In my case a single PHP script appends text strings to an existing text
> file. Several clients may trigger the same script on the same web page
> and thus more than one PHP instance might try to open and append text
> to the same file at the same time. I would assume that using flock()
> _does_ in fact prevent simultaneous access in this case. Am I correct?
> Thanks!
>
> Andrew[/color]

[abrtlt@yahoo.com]

Re: PHP instances writing to the same file?

Thanks. It's a server running on Linux.

Andrew


jon.tjemsland@g mail.com ha scritto:
[color=blue]
> What OS is the server that this script is running on? Flock will work
> to lock a file if you are running your script on a server with an OS
> that is compatible with flock. Both NFS and FAT file systems are
> incompatible.
>
> Here is a flock sample from (http://us3.php.net/flock):
>
> $fp = fopen("/tmp/lock.txt", "w+");
> if (flock($fp, LOCK_EX)) { // do an exclusive lock
> fwrite($fp, "Write something here\n");
> flock($fp, LOCK_UN); // release the lock
> } else {
> echo "Couldn't lock the file !";
> }
> fclose($fp);
>
>
> Regards
>
> Jon Tjemsland
>
>
> abrtlt@yahoo.co m wrote:[color=green]
> > I read in Programming PHP (O'Reilly) that flock() "cannot prevent two
> > PHP scripts running in the same web server process from accessing a
> > file at the same time".
> > In my case a single PHP script appends text strings to an existing text
> > file. Several clients may trigger the same script on the same web page
> > and thus more than one PHP instance might try to open and append text
> > to the same file at the same time. I would assume that using flock()
> > _does_ in fact prevent simultaneous access in this case. Am I correct?
> > Thanks!
> >
> > Andrew[/color][/color]