Re: Merge of nickrob-async-20060513 to mainline?

[Nick Roberts <nickrob at snap dot net dot nz>]

 > > Instead of GDB waiting for the enferior to stop directly, it creates a
 > > signal thread to do that.  This means that the main thread can continue to
 > > process the event loop.  When the inferior does stop, the signal thread
 > > writes to a file which GDB detects through handle_file_event in the event
 > > loop. It then calls inferior_event_handler.
 > 
 > OK, this is easily mimicable without threads, at least on GNU/Linux.

I'm starting to do this now.  I still use a pipe to write to a file descriptor
but instead of a separate thread I use a while loop in gdb_wait_for_event.
I've only done it for select because that's all I know but I guess a similar
thing could be done for poll.  It seems to work reasonably well for single
threaded inferiors but get's stuck again with multi-threaded ones.  The
multi-threaded code in linux-nat.c just seems so convoluted (maybe threads
are more easily handled with a Mach kernel).

Below is a (pseudo) diff fragment that should (hopefully) give the general
idea.  Do you mean something along these lines?  If yes, I'll try to get it
to work more generally.

-- 
Nick                                           http://www.inet.net.nz/~nickrob


*** linux-nat.c	18 Sep 2006 16:44:40 +1200	1.50

+ static int gdb_fetch_event (int* ptr_status)
+ {
+   struct timeval tv;
+   fd_set fds;
+   int msg[2], ret;
+ 
+   FD_ZERO (&fds);
+   FD_SET (gdb_status[0], &fds);
+   tv.tv_sec = 0;
+   tv.tv_usec = 0;
+ 
+   msg[0] = 0;
+   ret = select (FD_SETSIZE, &fds, NULL, NULL, NULL);
+   if (ret)
+     {
+       read (gdb_status[0], msg, 2*sizeof (int));
+       *ptr_status = msg[1];
+     }
+   
+   return msg[0];
+ }
+ 
  static ptid_t
  linux_nat_wait (ptid_t ptid, struct target_waitstatus *ourstatus)
  {
***************
*** 1956,1962 **** (linux_nat_wait)
      {
        pid_t lwpid;
  
!       lwpid = my_waitpid (pid, &status, options);
        if (lwpid > 0)
  	{
  	  gdb_assert (pid == -1 || lwpid == pid);
--- 2094,2106 ----
      {
        pid_t lwpid;
  
!       if (target_can_async_p () && gdb_post_startup)
! 	{
! 	  gdb_file_event = 0;
! 	  lwpid = gdb_fetch_event (&status);
! 	}
!       else
! 	lwpid = my_waitpid (pid, &status, options);
        if (lwpid > 0)
  	{
  	  gdb_assert (pid == -1 || lwpid == pid);


*** event-loop.c (gdb_wait_for_event) 11 Feb 2006 11:01:43 +1300	1.29

        gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0];
        gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1];
        gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2];
!       num_found = gdb_select (gdb_notifier.num_fds,
! 			      &gdb_notifier.ready_masks[0],
! 			      &gdb_notifier.ready_masks[1],
! 			      &gdb_notifier.ready_masks[2],
! 			      gdb_notifier.timeout_valid
! 			      ? &gdb_notifier.select_timeout : NULL);
  
        /* Clear the masks after an error from select. */
        if (num_found == -1)
--- 765,806 ----
        gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0];
        gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1];
        gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2];
! 
!       if (event_loop_p)
! 	{
! 	  struct timeval tv;
! 
! 	  while (num_found == 0)
! 	    {
! 	      msg[0] = waitpid (-1, ptr_status, WNOHANG);
!       
! 	      if (msg[0] > 0)
! 		{
! 		  msg[1] = *ptr_status;
! 		  write (gdb_status[1], msg, 2*sizeof (int));
! 		  gdb_file_event = 1;
! 		}
! 
! 	      tv.tv_sec = 0;
! 	      tv.tv_usec = 1000;
! 
! 	      gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0];
! 	      gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1];
! 	      gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2];
! 
! 	      num_found = gdb_select (gdb_notifier.num_fds,
! 				      &gdb_notifier.ready_masks[0],
! 				      &gdb_notifier.ready_masks[1],
! 				      &gdb_notifier.ready_masks[2],
! 				      &tv);
! 	    }
! 	} else
! 	num_found = gdb_select (gdb_notifier.num_fds,
! 				&gdb_notifier.ready_masks[0],
! 				&gdb_notifier.ready_masks[1],
! 				&gdb_notifier.ready_masks[2],
! 				gdb_notifier.timeout_valid
! 				? &gdb_notifier.select_timeout : NULL);