zend_alter_ini_entry threadsave if used in SAPI modules?

I am writing on an extension of the NSAPI SAPI module (see bug #8879) so that you can specify some overrides for php.ini entries at execution of a script from the webserver (like you can do it in apache). I want to set the variables with zend_alter_ini_entry(..., PHP_INI_SYSTEM, PHP_INI_STAGE_RUNTIME); but this call have no reference to TSRM. Can I use it or is it not thread save? e.g. if two requests to the webserver on two virtual servers run at the same time and each thread overwrites the doc_root property in php.ini can they coexist. Are PHP_INI_STAGE_RUNTIME settings only valid for one thread? Looking at aolserver SAPI, the ini feature is commented out there because of thread safety... Uwe