In my last post I had described how to circumvent some issues when compiling Wordpess 3.2.1 with Hiphop-Php. Unfortunately it came up that the compiled binary suffered from a memleak which took me quite some time to find and fix.
As it turned out hphp has a regular expression cache which caches every regular expression indefinitely such that clearing the cache is only possible if you shutdown the application. In principle this is not a problem for an application which has only a limited set of static regular expression patterns (which should be the case for most of the applications). But once the regex pattern becomes a runtime option the cache fails. This seems to be due to the fact that hphp compares cacheentries according to their regex-pattern hash and there is no guarantee that two equal dynamically allocated regex-pattern strings have the same hash. In the specific case of WordPress you have the runtime option to specify the date format which is mangled into a regex pattern somewhere inside the mysql2date function.
The obvious workaround is to limit the number of cacheentries. The specific commit can be found in my hiphop-php branch, which as the title says makes the PCRECache a least recently used cache. I strongly recommend those running a hphp-compiled WordPress to apply that patch. Feedback is as always welcome