APR file io, when compiled with APR_HAS_THREADS (the default unless it is specifically disabled or on a non-thread platform), is acquiring mutex locks on every buffered file read or write. That is lunacy. Whether or not locking is necessary must be decided by the caller, not by the library. The normal behavior is for buffers to be thread-specific, and thus never need mutexing.
BTW, the same can be said for pools -- right now it is locking all pool operations, even though the only ones that need locking are those shared by multiple threads (the global pools). Bogus. This stuff came up while Justin and Aaron were performance testing mod_mbox -- right now you can double the requests per second simply by recompiling with --disable-threads. ....Roy
