Edit report at http://bugs.php.net/bug.php?id=47227&edit=1
ID: 47227
Updated by: tony2...@php.net
Reported by: murphyk at yahoo-inc dot com
Summary: children forked with pcntl_fork release flock()s
created by parent
Status: Bogus
Type: Bug
Package: PCNTL related
Operating System: RHEL 4.4
PHP Version: 5.2.8
New Comment:
Just to make it clear - this issue has been fixed in revision 292632.
See this diff in trunk:
http://svn.php.net/viewvc/php/php-src/trunk/main/streams/plain_wrapper.c?r1=290578&r2=292632
Previous Comments:
------------------------------------------------------------------------
[2009-01-29 21:34:51] bfra...@php.net
So the problem is the new beefed up streams in 5.x that keeps the lock
state for a stream, where it didn't in 4.x.
5.x will unlock it when it cleans up the stream resource if it is
locked, look for php_stdiop_close in main/streams/plain_wrapper.c.
4.x would not unlock it and just clean up the handle by closing it,
which would leave it locked until the parent closed it or unlocked it.
While this is a bug, I don't think there is any real fix for it that can
happen
------------------------------------------------------------------------
[2009-01-28 15:13:05] murphyk at yahoo-inc dot com
I have RTFM, thanks.
>From the man 2 flock:
"Locks created by flock() are associated with a file, or, more
precisely, an open file table entry. This means that duplicate file
descriptors (created by, for example, fork(2) or dup(2)) refer to the
same lock, and this lock may be modified or released using any of
these descriptors. Furthermore, the lock is released either by an
explicit LOCK_UN operation on any of these duplicate descriptors, or
when all such descriptors have been closed."
"by an explicit LOCK_UN" - my child process did NOT call flock() in my
user code.
"or when all such descriptors have been closed" - my parent process
still has an open copy of the the filehandle.
To be clear, the "expected result" output is what happens in php4 - the
child closes the filehandle, but doesn't unlock the flock().
php5 appears to be explicitly unlocking all held flocks() during
shutdown. If this is intentional, fine, but it's not documented, and
it's a change in behavior between php4 and php5 which breaks previously
running code.
------------------------------------------------------------------------
[2009-01-28 08:44:50] j...@php.net
RTFM:
man 2 flock
man 2 fork
The behaviour is exactly how it should be and is.
------------------------------------------------------------------------
[2009-01-27 22:07:47] murphyk at yahoo-inc dot com
Description:
------------
The behavior of flock()ed files across forks appears to have changed
between php 4.4.8 and php 5.2.8.
Previously, children would inherit filehandles from their parent, and
would close() their copies of the filehandles on exit, but this would
not clear flock()s on the files locked in the parent.
Now, it appears that if any child exits(), this will clear flock()s on
any filehandles inherited from the parent.
Reproduce code:
---------------
<?php
$fp = fopen("/tmp/lock.txt", "w+");
if (flock($fp, LOCK_EX + LOCK_NB )) {
print "Got lock.\n";
} else {
print "Couldn't lock the file.\n";
exit();
}
$pid = pcntl_fork();
if ($pid) {
pcntl_waitpid($pid,$status);
}
else {
exit();
}
sleep(100);
?>
Expected result:
----------------
$ php flock.php &
[1] 22054
$ Got lock.
$ php flock.php
Couldn't lock the file.
Actual result:
--------------
$php flock.php &
[1] 31085
$Got lock.
$php flock.php
Got lock.
------------------------------------------------------------------------
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Edit this bug report at http://bugs.php.net/bug.php?id=47227&edit=1
