equivalent of perl's ithread

As of perl 5.6, perl has a concept of interpreter thread (called ithread). Basically, any variable that you want to be shared across threads, you have to explicitly shared it. This apply not only to regular variables, but also apply to super global variables such as $_, making it easy to write threadsafe modules in perl. Does PHP has an equivalent concept? If I am developing php pages that are to be run under apache2 threaded worker mpm, can I use $_SERVER variable ? Thanks Khai