Edit report at https://bugs.php.net/bug.php?id=63709&edit=1
ID: 63709
Comment by: mi+php at aldan dot algebra dot com
Reported by: eric dot saintetienne at gmail dot com
Summary: flock() doesn't trigger mandatory locks on linux
Status: Analyzed
Type: Bug
Package: Filesystem function related
Operating System: Linux
PHP Version: 5.3.19
Block user comment: N
Private report: N
New Comment:
Eric, I'm confused. Are you saying, the problem I am illustrating with my test
case is different? Should I file a separate bug-report?
Previous Comments:
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[2013-04-04 08:32:28] eric dot saintetienne at gmail dot com
I appreciate your code and efforts but please stay focus on the topic:
MANDATORY
locks only. The issue is that PHP doesn't provide a standard way of triggering
a
mandatory lock.
MANDATORY locks are specific to Linux and occurs on a volume that is mounted
with the "-o mand" mount flag.
ADVISORY locks exist on any system via flock() or lockf() calls and are not the
subject of this thread.
Now I'm speaking to PHP developpers: how do you plan to fill in the gap?
Thanks
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[2013-04-04 01:49:17] mi+php at aldan dot algebra dot com
This is my test case:
<?php
function warn($message) {
global $argv;
fputs(STDERR, "$argv[0]: $message\n");
}
function add_dir($dir) {
$lname = $dir . '/distd.pid';
$lock = fopen($lname, 'c+');
if (!$lock) {
warn("$lname: can not open");
return FALSE;
}
if (!flock($lock, LOCK_EX|LOCK_NB)) {
warn("$lname: can not lock");
return FALSE;
}
warn(getmypid() . " ". date('H:i:s') . " $lname successfully locked");
return (fputs($lock, getmypid() . "\n". gethostname() . "\n") != FALSE);
}
date_default_timezone_set('America/New_York');
add_dir('/tmp');
sleep(3);
warn(getmypid() . " ". date('H:i:s') . " exiting in peace");
?>
Running TWO of the above in parallel:
% ( php t.php < /dev/null & php t.php < /dev/null ) >& l
I see BOTH of them claim to have "successfully" gotten the lock:
% cat l
[1] 26815
t.php: 26815 21:48:34 /tmp/distd.pid successfully locked
t.php: 26814 21:48:34 /tmp/distd.pid successfully locked
t.php: 26815 21:48:37 exiting in peace
t.php: 26814 21:48:37 exiting in peace
------------------------------------------------------------------------
[2013-04-02 07:58:42] eric dot saintetienne at gmail dot com
I hope we're still speaking of MANDATORY locks (the ones provided by "mount -o
mand") and not standard file locks? Other locks (advisory) behave as expected.
So what's the solution you chose to allow locking a file with a MANDATORY lock
using PHP?
------------------------------------------------------------------------
[2013-04-01 23:01:23] mi+php at aldan dot algebra dot com
I am puzzled, what can the current behavior be possibly used for?
If the lock is not really locking (and it does not -- neither on Linux nor on
FreeBSD), then why bother with it at all? And if nobody bothers, then why not
fix it properly?
BTW, at least, on BSD the different locking mechanisms create compatible locks:
The flock(), fcntl(2), and lockf(3) locks are compatible.
Processes using different locking interfaces can cooperate
over the same file safely. However, only one of such interfaces
should be used within the same process. If a file is locked by
a process through flock(), any record within the file will be
seen as locked from the viewpoint of another process using
fcntl(2) or lockf(3), and vice versa.
------------------------------------------------------------------------
[2012-12-07 09:43:12] eric dot saintetienne at gmail dot com
You're right, Python is smart and the trick is simple: fnctl module functions
are coded such that they detect the type of the object they're given as
argument. If it's an integer they assume it is a file descriptor otherwise they
call its fileno() method to retrieve the file descriptor integer.
So it's a matter of adding your own fileno() method to the PHP standard file
object and making the dio_* routines calling it, when not provided with an
integer.
Does that makes sense to you?
It's a suggestion, at the end of the day it's your decision of how to handle
this issue, even though it seems to, I'm actually not pushing to get direct io
integrated at any cost (I don't have any stake) but I just feel it's the way to
go.
------------------------------------------------------------------------
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