Hello Uwe,
Wednesday, December 3, 2003, 6:06:13 PM, you wrote:
> 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...)
Why not simply use external iteration? You don't add or modify the browser
list right?
--
Best regards,
Marcus mailto:helly@php.net
