From: chris_se at gmx dot net
Operating system: Any POSIX-compatible OS
PHP version: 5.2.4
PHP Bug Type: Streams related
Bug description: file_put_contents' LOCK_EX flag is useless with advisory
locking
Description:
------------
The LOCK_EX flag of file_put_contents suggests that the function will use
an advisory lock to ensure transaction safety. This is NOT the case (except
when combined with FILE_APPEND). It actually DOES request an exclusive lock
on the file but only does so AFTER opening it in the 'wb' mode which will
truncate the file on opening BEFORE the actual lock can be acquired.
The correct behaviour would be to open the file for writing without
truncating it, in C for example using
int fileno = open (file, O_WRONLY | O_CREAT, 0666);
(WITHOUT adding O_TRUNC!), THEN acquiring the lock using flock() and THEN
truncating the file to 0 bytes length.
I don't know if there's a simple possibility to integrate it with the
current streams API (since there's no fopen mode that will map to either
O_WRONLY | O_CREAT or O_RWDR | O_CREAT) but if it's not possible to fix it,
you should at least remove the option, since it suggests something it can't
provide with advisory locking.
This is not a problem on Windows since Windows locks are always mandatory.
Reproduce code:
---------------
First script (start in in a first window using any P):
<?php
file_put_contents ('file.txt', 'Hello World!');
$f = fopen ('file.txt', 'r') or die ("Could not open file!\n");
flock ($f, LOCK_SH) or die ("Could not acaquire lock!\n");
echo "Sleeping for 20 seconds (please use file_put_contents script in the
mean time!)\n";
sleep (20);
$x .= fread ($f, 1024);
fclose ($f);
echo "Contents was: '" . $x . "'\n";
?>
Second script (start it in a second window in the same directory while the
first one is sleeping):
<?php
file_put_contents ('file.txt', 'ByeBye Joe!', LOCK_EX);
?>
Expected result:
----------------
The first script should output:
Sleeping for 20 seconds (please use file_put_contents script in the mean
time!)
Contents was: 'Hello World!'
Actual result:
--------------
The first script outputs:
Sleeping for 20 seconds (please use file_put_contents script in the mean
time!)
Contents was: ''
--
Edit bug report at http://bugs.php.net/?id=43182&edit=1
--
Try a CVS snapshot (PHP 4.4):
http://bugs.php.net/fix.php?id=43182&r=trysnapshot44
Try a CVS snapshot (PHP 5.2):
http://bugs.php.net/fix.php?id=43182&r=trysnapshot52
Try a CVS snapshot (PHP 5.3):
http://bugs.php.net/fix.php?id=43182&r=trysnapshot53
Try a CVS snapshot (PHP 6.0):
http://bugs.php.net/fix.php?id=43182&r=trysnapshot60
Fixed in CVS: http://bugs.php.net/fix.php?id=43182&r=fixedcvs
Fixed in release:
http://bugs.php.net/fix.php?id=43182&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=43182&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=43182&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=43182&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=43182&r=support
Expected behavior: http://bugs.php.net/fix.php?id=43182&r=notwrong
Not enough info:
http://bugs.php.net/fix.php?id=43182&r=notenoughinfo
Submitted twice:
http://bugs.php.net/fix.php?id=43182&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=43182&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=43182&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=43182&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=43182&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=43182&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=43182&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=43182&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=43182&r=mysqlcfg
