Blocking with fopen when file is already open for writing

[Efi Merdler]

Hi,
I created a very simple application that reads and writes to a file, I
was wondering if fopen when opening a file for write access blocks
this file, i.e. when another user runs this script the script will
halt until the first user closes its file handle.

If not how can I change php behavior to block such access?

Thank you,
Efi

[Gordon Burditt]

Re: Blocking with fopen when file is already open for writing

>I created a very simple application that reads and writes to a file, I

>was wondering if fopen when opening a file for write access blocks
>this file, i.e. when another user runs this script the script will
>halt until the first user closes its file handle.

You can pretty much count on PHP *not* automatically doing this for
you. For one thing, there are safe ways of two processes both
having the same file open for write and *not* clobbering each other
(e.g. each writes only to its own pre-existing record) that PHP
shouldn't prohibit it.

>If not how can I change php behavior to block such access?

All users of the file can use flock().

[Colin McKinnon]

Re: Blocking with fopen when file is already open for writing

Efi Merdler wrote:

Hi,
I created a very simple application that reads and writes to a file, I
was wondering if fopen when opening a file for write access blocks
this file, i.e. when another user runs this script the script will
halt until the first user closes its file handle.
>

What happenned when you tested it?

Here's a hint:
<?php
print "ready to start\n";
flush();
$fh=fopen('/tmp/test','w');
if (is_resource($f h)) {
print "opened...\ n";
flush();
sleep(30);
print "Exiting\n" ;
fclose($fh);
} else {
print "failed to open\n";
}
?>

(if you run two instances of this script, the second will do one of three
things - you've only considered two possibilities so far)

If not how can I change php behavior to block such access?
>

flock()

C.

[Efi Merdler]

Re: Blocking with fopen when file is already open for writing


Colin McKinnon wrote:

Efi Merdler wrote:
>

Hi,
I created a very simple application that reads and writes to a file, I
was wondering if fopen when opening a file for write access blocks
this file, i.e. when another user runs this script the script will
halt until the first user closes its file handle.

>
What happenned when you tested it?
>
Here's a hint:
<?php
print "ready to start\n";
flush();
$fh=fopen('/tmp/test','w');
if (is_resource($f h)) {
print "opened...\ n";
flush();
sleep(30);
print "Exiting\n" ;
fclose($fh);
} else {
print "failed to open\n";
}
?>
>
(if you run two instances of this script, the second will do one of three
things - you've only considered two possibilities so far)
>

If not how can I change php behavior to block such access?

>
flock()
>
C.

Thanks,
I'll probably use a semaphore in order achieve this block behavior.

Efi

[Drazen Gemic]

Re: Blocking with fopen when file is already open for writing

On Mar 4, 12:21 am, Colin McKinnon
<colin.thisisno tmysurn...@ntlw orld.deletemeun lessURaBot.comw rote:

I think that Windows will lock file exclusively, by default. UNIX and
similar systems will
not, by default.

DG

[NC]

Re: Blocking with fopen when file is already open for writing

On Mar 3, 5:06 am, "Efi Merdler" <foo...@gmail.c omwrote:

>
I created a very simple application that reads and writes to a file, I
was wondering if fopen when opening a file for write access blocks
this file, i.e. when another user runs this script the script will
halt until the first user closes its file handle.

Nothing of the sort. You need to expressly lock the file using
flock(),
which, alas, will not help you on Windows due to Windows' thread
model.

Cheers,
NC

[NC]

Re: Blocking with fopen when file is already open for writing

On Mar 4, 6:15 am, "Drazen Gemic" <trench...@yaho o.comwrote:

>
I think that Windows will lock file exclusively, by default.

Maybe, but since all instances of the script will run under the same
process ID (although they may have different thread IDs), it's not
going to help; the file will remain writeable to all instances of the
script.

Cheers,
NC

[Efi Merdler]

Re: Blocking with fopen when file is already open for writing


Colin McKinnon wrote:

Efi Merdler wrote:
>

Hi,
I created a very simple application that reads and writes to a file, I
was wondering if fopen when opening a file for write access blocks
this file, i.e. when another user runs this script the script will
halt until the first user closes its file handle.

>
What happenned when you tested it?
>
Here's a hint:
<?php
print "ready to start\n";
flush();
$fh=fopen('/tmp/test','w');
if (is_resource($f h)) {
print "opened...\ n";
flush();
sleep(30);
print "Exiting\n" ;
fclose($fh);
} else {
print "failed to open\n";
}
?>
>
(if you run two instances of this script, the second will do one of three
things - you've only considered two possibilities so far)
>

If not how can I change php behavior to block such access?

>
flock()
>
C.

Hi,
Thanks for the hint.
I tried to use a semaphore, however my php was not compiled with the
right flag, so I'm left with flock, I tested its behavior using your
scripts, it works as expected.

Efi