Major Win32 multithreading overheal. The changes are:

 - Replaced assert()'s with aplog_errors() in various places, so that
   we don't loose error checking in the release build. Also asserts()
   do an ungraceful exit - try to be kinder to the user.

 - Added some debug macros to send messages to the screen or error log
   (these are just for convenience - if you don't like them they can
   be removed) (APD1() thru APD5()).

 - Add model-independent functions to initiate a restart or shutdown.
   Currently this is initiated in functions which know they are being
   called as a signal handler. This is now abstracted to a separate
   functions, which can be called from a signal handler, or on Win32
   from the service controller callback. (start_shutdown(),
   start_restart())

 - Added lots of comments to the MT part of the code probably containing
   lots of tyops, er, typos.

 - In child_sub_main() (the "worker" thread code) used ptrans for
   the temporary pool, instead of pchild - now consistent with
   Unix child_main() [Incidently I'm not sure why ptrans is a global,
   since it (should) only be used within child_main()?]

 - made the parent thread (worker_main()) exit without going into the
   main parent loop if it is being signalled to die. Create the child
   pool (pchild) here (since this pool has a lifetime of a process,
   not a "child" (thread)). Cleanup this pool on exit, and run
   child_exit_modules().

 - worker_main() now will not exit until all the connections in its
   listen() queue are dealt with (previous it would "count_down" a
   few requests, then die, which would loose the connections in
   this process'es listen() queue). This now makes graceful restarts not
   loose connections. Once worker_main() has been told to exit it
   frees the mutex to allow another worker_main() to get into a listen()
   [however it seems Win32 directs incoming requests to the first process
   annoyingly]. To give the old worker_main() a chance to exit,
   only sleep for 1 second in the select. Also catch problems if the
   select() returns immediately with an error (previously this would
   cause a busy loop forever).

 - In the parent process (master_main()) abstract the creation/removal
   of processes (create_process(), cleanup_process()). Only bother to
   create one child process at once (more are unnecessary). Use an event
   to simulate a signal (with variables used to determine what action
   should be taken). Block forever waiting for a child to die or for
   the "signal" event (previously it would loop every 2 seconds). Handle
   shutdowns and restarts (both graceful). Allow multiple graceful
   restarts. Log error conditions like when child processes have to
   be forcibly terminated.

 - Update os/win32/service.c so that a "net stop apache" sends a
   graceful shutdown "signal" (using start_shutdown()). By changing
   this to call start_restart() you can also test graceful restarts.

 - Some unused code to do ungraceful shutdown/restart. Currently
   mutually exclusive with graceful restarts. Not compiled in by
   default. See the comments about UNGRACEFUL_RESTARTS in the patch.

On the downside, this patch

 - Makes the MT code more Win32 specific (this is necessary since
   it is useful to do WaitForMultipleObject() type things, for instance,
   and we don't have an abstraction for that). Also the Win32 stuff should
   use completion ports, and again we don't have an abstraction. However
   this does give us a good idea of stuff that does need abstracting.

 - I haven't checked for resource leaks, proper pool maintenence, or
   proper sequences of module init/child init/child exit API calls.

 - Makes http_main.c even bigger. I was going to split it out in
   core, multi-process and MT parts at the outset but that would
   have made comparing the patch pretty difficult. However I think it
   is a good idea to move the code in the #ifdef MULTITHREAD/#endif
   part to a separate http_main_mt.c (or maybe a http_main_win32 since
   it is quite specific at the moment).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@79827 13f79535-47bb-0310-9956-ffa450edef68