そういえばこんな話もあったような．むしろ1プロセスだけにしてしまった方がいい!?

　　* FreeBSD, threads, and worker MPM. All seems to work fine
　　　if you only have one worker process with many threads. Add
　　　a second worker process and the accept lock seems to be
　　　lost. This might be an APR issue with how it deals with
　　　the child_init hook (i.e. the fcntl lock needs to be resynced).
　　　More examination and analysis is required.
　　　　Status: Works with FreeBSD 5.3. Does not work in previous versions.
　　　　　　　　This has also been reported on Cygwin.