taxonomy bug with microtime

[_jameslee]

in the ~/wp_includes/taxonomy->get_terms() function
the $last_changed if it was not set, it gets set to what ever the microtime() is at that moment. previous versions of this file it was time(), unless you call microtime with the bool of true, you will get a space in between the "msec sec". now this is fine and dandy, but if you are running memcached as your caching device, the space in the cache key causes all sort of weird things to happen.

here's my diff for this file.

Index: taxonomy.php
===================================================================
--- taxonomy.php	(revision 26930)
+++ taxonomy.php	(working copy)
@@ -1313,7 +1313,7 @@
 	$key = md5( serialize( compact(array_keys($defaults)) ) . serialize( $taxonomies ) . $filter_key );
 	$last_changed = wp_cache_get( 'last_changed', 'terms' );
 	if ( ! $last_changed ) {
-		$last_changed = microtime();
+		$last_changed = microtime(true);
 		wp_cache_set( 'last_changed', $last_changed, 'terms' );
 	}
 	$cache_key = "get_terms:$key:$last_changed";

Can someone please also update the docblock as well? it has had changes since version 2.3

[nacin]

Hi _jameslee, this looks good, thanks! We use microtime() in a few other spots and should validate all of those are good as well.

[_jameslee]

class-phpass.php:52:		$this->random_state = microtime() . uniqid(rand(), TRUE); // removed getmypid() for compatibility reasons
class-phpass.php:68:				    md5(microtime() . $this->random_state);
class-snoopy.php:1215:				$this->_mime_boundary = "Snoopy".md5(uniqid(microtime()));
comment.php:283:			$last_changed = microtime();
comment.php:1563:	wp_cache_set( 'last_changed', microtime(), 'comment' );
comment.php:2363:	wp_cache_set( 'last_changed', microtime(), 'comment' );
general-template.php:988:		$last_changed = microtime();
pluggable.php:1612:		$rnd_value = md5( uniqid(microtime() . mt_rand(), true ) . $seed );
post.php:3752:		$last_changed = microtime();
post.php:4766:	wp_cache_set( 'last_changed', microtime(), 'posts' );
taxonomy.php:1316:		$last_changed = microtime();
taxonomy.php:2805:	wp_cache_set( 'last_changed', microtime(), 'terms' );

here is the list of all microtime usage in the wp-includes directory that do not have the bool value set.

[drozdz]

I've changed this only in parts, where it's used as cache key.

I'm pretty sure there is no point in changing this also in places, where microtime is called only to generate md5, unique ids and random values.

[nacin]

In 27115:

Use a float for last_changed microtime cache values.

microtime() by default returns a string with a space, which isn't allowed for keys in some cache backends.

props _jameslee, drozdz.
fixes #27000. see #23448.

[westi]

Nice find @_jameslee - I'm curious which memcache object cache back end you are using because this one ​http://wordpress.org/plugins/memcached/ has stripped whitespace from key names since 2006 thereby hiding these bugs from us :)

[_jameslee]

we have a very old version of object-cache.php version 0.42 basically an old WPMU version. we will upgrading this very soon. Thanks!

[SergeyBiryukov]

[27115] introduced a race condition in taxonomy unit tests, see ticket:14485:95.

[nacin]

In 27300:

Revert [27115] and let cache backends handle the stripping of spaces in cache keys as necessary.

microtime() returns greater precision than microtime(true).

see #27000, #23448, #26903, #14485.