Edit report at https://bugs.php.net/bug.php?id=50688&edit=1
ID: 50688
Comment by: eric_haney at yahoo dot com
Reported by: jcampbell at remindermedia dot com
Summary: Using exceptions inside usort() callback function
causes a warning
Status: Assigned
Type: Bug
Package: Arrays related
Operating System: Fedora Core 12
PHP Version: 5.*, 6
Assigned To: stas
Block user comment: N
Private report: N
New Comment:
It took me a while to figure out that some code called from usort was throwing,
catching, and (gracefully) handling an Exception. Then I found this post.
Quite frustrating.
I turned off warnings with ini_set before calling usort, then turned them on
again after. This is an effective workaround for now, but I'd love to clean
that nastiness out of my code.
It is also my opinion that usort should be allowed to change the elements in
the array. EG: an instance variable of an object may be lazy-loaded as a
result of a method call from within a usort callback. Should a warning really
be issued in that case?
Previous Comments:
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[2011-10-10 21:44:56] poehler at interworx dot com
This bug is still present as of PHP 5.3.8, we ran into it today and spent most
of a day trying to figure out what was causing the error message "Array was
modified by the user comparison function", when CLEARLY, NOTHING was changing
the array at all!
The exception was not thrown/caught directly in the usort function but rather
in a constructor of a class that was called about 3 or 4 functions deep from
the usort, making it very difficult to track down.
After finally figuring out the exception was somehow related, we searched
google and found this bug report. I'm sure we can agree that the minor act of
catching an exception should not result in usort throwing a warning message.
This bug is a huge timewaster :(
------------------------------------------------------------------------
[2010-10-07 23:34:54] philipwhiuk at hotmail dot com
I notice this is still affecting PHP 5.3.3 (Windows/Apache install).
Is this likely to be fixed soon - is it a question of developer time and
priority
or is it too difficult to fix?
It's quite irritating - I realise that the obvious solution is to avoid
throwing
the exception (ha-ha) but it's a useful function and exceptions are...
inevitable.
------------------------------------------------------------------------
[2010-05-31 17:24:05] ajrattink at correct dot net
I printed a debug line from my usort callback. It called debug_backtrace() to
print the line and sourcefile in the debuglog. And therefor triggered the
error. Even more, it did not sort.
Maybe the phpmanual should state that usort() callbacks are not allowed to
write loglines. I also think that usort() callbacks that DO change the array
are perfectly legal, as long as they don't change the sort.
Maybe your sorter code needs stackoverflow protection or whatever, but calling
certain code 'invalid', because it causes your code to SEGV is a stupid way to
solve a bug.
------------------------------------------------------------------------
[2010-04-01 02:12:52] s...@php.net
The reason seems to be that when making exception backtrace,
debug_backtrace_get_args() uses SEPARATE_ZVAL_TO_MAKE_IS_REF() on arguments,
which makes it look as if the argument was indeed modified (which usort is
designed to protect against, since cmp callback is not supposed to modify the
arguments)
------------------------------------------------------------------------
[2010-03-05 17:41:30] bernie at dcbl dot ca
affects gentoo builds after > 5.2.10 (5.2.11, 5.2.11-r1, and 5.2.12)
------------------------------------------------------------------------
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