Re: browscap and nesting level too deep (bug #25916)

We have thread-safe hashes in php5; browscap should probably use one of those there. If you want to roll your own protection, take a look at tsrm_mutex_lock() and tsrm_mutex_unlock() and how they are used in ext/yaz. --Wez. ----- Original Message ----- From: "Uwe Schindler" <uwe@thetaphi.de> To: <jay@php.net>; <internals@lists.php.net> Sent: Wednesday, December 03, 2003 5:06 PM Subject: [PHP-DEV] browscap and nesting level too deep (bug #25916) > Today I got the error from bug #25916 several times on our webserver. > Looking through the code I found out the following: > * It depends NOT on the fact if there is a parameter to get_browser() or not > * It happens sometimes when server is very heavy loaded, the homepage of > the domain uses the get_browser() function and is the most visited page. > > So it must be a multithreading issue (NSAPI is a multithreading webserver). > And I have an idea: > Line 257 uses: > zend_hash_apply_with_arguments(&browser_hash, (apply_func_args_t) > browser_reg_compare, 2, lookup_browser_name, &found_browser_entry); > > This is the only function in this context in zend_hash.c which uses the > Recursion protection with > #define > HASH_PROTECT_RECURSION(ht) > \ > if ((ht)->bApplyProtection) > { > \ > if ((ht)->nApplyCount++ >= 3) > { > \ > zend_error(E_ERROR, "Nesting level too deep - > recursive dependency?"); \ > } > \ > } > > The browser hashtable is a global variable in browscap.c and can be used by > more than one call to get_browser() even at the same time. So if one > zend_hash_apply_with_arguments() locks the hashtable and a second and third > thread tries to do that you will get the error, because (ht)->nApplyCount++ > raises and raises... > > This evening I will try to put a mutex at the beginning of get_browser to > prevent more threads running at the same time there. But as I see this, > this zend_hash_apply function is used very often could there be other > effects if a global variable is a hashtable? > > Only one question: Is there a special PHP way to use mutexes? I am not > familar in Zend programming (I do only SAPI...)