My impression is yes that it is and that this is why mod_php shops run it (usually for non-thread safe apps).
On my ubuntu box, if I run
sudo ps axo pid,ppid,rss,vsz,nlwp,cmd
I get this:
32305 1 9820 183732 1 /usr/sbin/apache2 -k start 32318 32305 7172 183732 1 /usr/sbin/apache2 -k start
the nlwp would suggest apache is running as a single-threaded app or am I missing something?
Also - does this mean that all apache modules will be run in these apache processes as single threaded? Does the single threading nature of the parent process basically force these modules into acting as single threaded?