Re: More info on sporadic OS/X crash

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On 27 Apr 2004 17:24:36 +0200, Piet van Oostrum <piet@cs.uu.nl> said:

> However now I have occasional hangs in select(), always when using
> gnus.  It could be a server that is not responding, but I am not
> sure. 

I encountered the following situation (though I'm not sure whether it
is related to the above one):

   1. select (actually, sys_select in mac.c) is called from
      wait_reading_process_input.
   2. Interrupt by SIGALRM occurs while ReceiveNextEvent in sys_select
      is being processed.
   3. ReceiveNextEvent is called from XTread_socket again.
   4. Emacs hangs.

So at least ReceiveNextEvent in sys_select must be enclosed with
BLOCK_INPUT/UNBLOCK_INPUT.

Below is the sys_select function currently I'm using.  Besides the
above issue, I also modified the calculation of the remaining time for
timeout and added a special handling for the common case where there
are no subprocesses to be monitored.

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp

#include "blockinput.h"
int
sys_select (n, rfds, wfds, efds, timeout)
  int n;
  SELECT_TYPE *rfds;
  SELECT_TYPE *wfds;
  SELECT_TYPE *efds;
  struct timeval *timeout;
{
  OSErr err;
  EMACS_TIME end_time, now, remaining_time;

  if (inhibit_window_system || noninteractive
      || rfds == NULL || !FD_ISSET (0, rfds))
    return select(n, rfds, wfds, efds, timeout);

  if (wfds == NULL && efds == NULL)
    {
      int i;

      for (i = 1; i < n; i++)
	if (FD_ISSET (i, rfds))
	  break;
      if (i == n)
	{
	  EventTimeout timeout_sec =
	    (timeout
	     ? (EMACS_SECS (*timeout) + EMACS_USECS (*timeout) / 1000000.0)
	     : kEventDurationForever);

	  BLOCK_INPUT;
	  err = ReceiveNextEvent (0, NULL, timeout_sec, false, NULL);
	  UNBLOCK_INPUT;
	  if (err == noErr)
	    {
	      FD_ZERO (rfds);
	      FD_SET (0, rfds);
	      return 1;
	    }
	  else
	    return 0;
	}
    }

  if (timeout)
    {
      remaining_time = *timeout;
      EMACS_GET_TIME (now);
      EMACS_ADD_TIME (end_time, now, remaining_time);
    }

  FD_CLR (0, rfds);
  do
    {
      EMACS_TIME select_timeout;
      SELECT_TYPE orfds = *rfds;
      int r;

      EMACS_SET_SECS_USECS (select_timeout, 0, 20000);

      if (timeout && EMACS_TIME_LT (remaining_time, select_timeout))
	select_timeout = remaining_time;

      r = select (n, &orfds, wfds, efds, &select_timeout);
      BLOCK_INPUT;
      err = ReceiveNextEvent (0, NULL, kEventDurationNoWait, false, NULL);
      UNBLOCK_INPUT;
      if (r > 0)
	{
	  *rfds = orfds;
	  if (err == noErr)
	    {
	      FD_SET (0, rfds);
	      r++;
	    }
	  return r;
	}
      else if (err == noErr)
	{
	  FD_ZERO (rfds);
	  FD_SET (0, rfds);
	  return 1;
	}

      if (timeout)
	{
	  EMACS_GET_TIME (now);
	  EMACS_SUB_TIME (remaining_time, end_time, now);
	}
    }
  while (!timeout || EMACS_TIME_LT (now, end_time));

  return 0;
}