newlib-cygwin/winsup/cygwin/select.cc

/* select.cc

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

/* The following line means that the BSD socket definitions for
   fd_set, FD_ISSET etc. are used in this file.  */

#define  __INSIDE_CYGWIN_NET__

#include "winsup.h"
#include <stdlib.h>
#include <sys/param.h>
#include "ntdll.h"

#define USE_SYS_TYPES_FD_SET
#include <winsock2.h>
#include <netdb.h>
#include "cygerrno.h"
#include "security.h"
#include "path.h"
#include "fhandler.h"
#include "select.h"
#include "dtable.h"
#include "cygheap.h"
#include "pinfo.h"
#include "sigproc.h"
#include "cygtls.h"

/*
 * All these defines below should be in sys/types.h
 * but because of the includes above, they may not have
 * been included. We create special UNIX_xxxx versions here.
 */

#ifndef NBBY
#define NBBY 8    /* number of bits in a byte */
#endif /* NBBY */

/*
 * Select uses bit masks of file descriptors in longs.
 * These macros manipulate such bit fields (the filesystem macros use chars).
 * FD_SETSIZE may be defined by the user, but the default here
 * should be >= NOFILE (param.h).
 */

#define UNIX_NFDBITS (sizeof (fd_mask) * NBBY)       /* bits per mask */
#ifndef unix_howmany
#define unix_howmany(x,y) (((x)+((y)-1))/(y))
#endif

#define unix_fd_set fd_set

#define NULL_fd_set ((fd_set *) NULL)
#define sizeof_fd_set(n) \
  ((size_t) (NULL_fd_set->fds_bits + unix_howmany ((n), UNIX_NFDBITS)))
#define UNIX_FD_SET(n, p) \
  ((p)->fds_bits[(n)/UNIX_NFDBITS] |= (1L << ((n) % UNIX_NFDBITS)))
#define UNIX_FD_CLR(n, p) \
  ((p)->fds_bits[(n)/UNIX_NFDBITS] &= ~(1L << ((n) % UNIX_NFDBITS)))
#define UNIX_FD_ISSET(n, p) \
  ((p)->fds_bits[(n)/UNIX_NFDBITS] & (1L << ((n) % UNIX_NFDBITS)))
#define UNIX_FD_ZERO(p, n) \
  memset ((caddr_t) (p), 0, sizeof_fd_set ((n)))

#define allocfd_set(n) ({\
  size_t __sfds = sizeof_fd_set (n) + 8; \
  void *__res = alloca (__sfds); \
  memset (__res, 0, __sfds); \
  (fd_set *) __res; \
})

#define set_handle_or_return_if_not_open(h, s) \
  h = (s)->fh->get_handle (); \
  if (cygheap->fdtab.not_open ((s)->fd)) \
    { \
      (s)->thread_errno =  EBADF; \
      return -1; \
    }

static int select (int, fd_set *, fd_set *, fd_set *, LONGLONG);

/* The main select code.  */
extern "C" int
pselect (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
	const struct timespec *to, const sigset_t *set)
{
  sigset_t oldset = _my_tls.sigmask;

  __try
    {
      if (set)
	set_signal_mask (_my_tls.sigmask, *set);

      select_printf ("pselect (%d, %p, %p, %p, %p, %p)", maxfds, readfds, writefds, exceptfds, to, set);

      pthread_testcancel ();
      int res;
      if (maxfds < 0)
	{
	  set_errno (EINVAL);
	  res = -1;
	}
      else
	{
	  /* Convert to microseconds or -1 if to == NULL */
	  LONGLONG us = to ? to->tv_sec * USPERSEC
			     + (to->tv_nsec + (NSPERSEC/USPERSEC) - 1)
			       / (NSPERSEC/USPERSEC)
			   : -1LL;

	  if (to)
	    select_printf ("to->tv_sec %ld, to->tv_nsec %ld, us %D", to->tv_sec, to->tv_nsec, us);
	  else
	    select_printf ("to NULL, us %D", us);

	  res = select (maxfds, readfds ?: allocfd_set (maxfds),
			writefds ?: allocfd_set (maxfds),
			exceptfds ?: allocfd_set (maxfds), us);
	}
      syscall_printf ("%R = select (%d, %p, %p, %p, %p)", res, maxfds, readfds,
		      writefds, exceptfds, to);

      if (set)
	set_signal_mask (_my_tls.sigmask, oldset);
      return res;
    }
  __except (EFAULT) {}
  __endtry
  return -1;
}

/* select () is just a wrapper on pselect (). */
extern "C" int
cygwin_select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
	       struct timeval *to)
{
  struct timespec ts;
  if (to)
    {
      ts.tv_sec = to->tv_sec;
      ts.tv_nsec = to->tv_usec * 1000;
    }
  return pselect (maxfds, readfds, writefds, exceptfds,
		  to ? &ts : NULL, NULL);
}

/* This function is arbitrarily split out from cygwin_select to avoid odd
   gcc issues with the use of allocfd_set and improper constructor handling
   for the sel variable.  */
static int
select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
	LONGLONG us)
{
  select_stuff::wait_states wait_state = select_stuff::select_set_zero;
  int ret = 0;

  /* Record the current time for later use. */
  LONGLONG start_time = get_clock (CLOCK_REALTIME)->usecs ();

  select_stuff sel;
  sel.return_on_signal = 0;

  /* Allocate fd_set structures to store incoming fd sets. */
  fd_set *readfds_in = allocfd_set (maxfds);
  fd_set *writefds_in = allocfd_set (maxfds);
  fd_set *exceptfds_in = allocfd_set (maxfds);
  memcpy (readfds_in, readfds, sizeof_fd_set (maxfds));
  memcpy (writefds_in, writefds, sizeof_fd_set (maxfds));
  memcpy (exceptfds_in, exceptfds, sizeof_fd_set (maxfds));

  do
    {
      /* Build the select record per fd linked list and set state as
	 needed. */
      for (int i = 0; i < maxfds; i++)
	if (!sel.test_and_set (i, readfds_in, writefds_in, exceptfds_in))
	  {
	    select_printf ("aborting due to test_and_set error");
	    return -1;	/* Invalid fd, maybe? */
	  }
      select_printf ("sel.always_ready %d", sel.always_ready);

      if (sel.always_ready || us == 0)
	/* Catch any active fds via sel.poll () below */
	wait_state = select_stuff::select_ok;
      else
	/* wait for an fd to become active or time out */
	wait_state = sel.wait (readfds, writefds, exceptfds, us);

      select_printf ("sel.wait returns %d", wait_state);

      if (wait_state == select_stuff::select_ok)
	{
	  UNIX_FD_ZERO (readfds, maxfds);
	  UNIX_FD_ZERO (writefds, maxfds);
	  UNIX_FD_ZERO (exceptfds, maxfds);
	  /* Set bit mask from sel records.  This also sets ret to the
	     right value >= 0, matching the number of bits set in the
	     fds records.  if ret is 0, continue to loop. */
	  ret = sel.poll (readfds, writefds, exceptfds);
	  if (ret < 0)
	    wait_state = select_stuff::select_signalled;
	  else if (!ret)
	    wait_state = select_stuff::select_set_zero;
	}
      /* Always clean up everything here.  If we're looping then build it
	 all up again.  */
      sel.cleanup ();
      sel.destroy ();
      /* Check and recalculate timeout. */
      if (us != -1LL && wait_state == select_stuff::select_set_zero)
	{
	  select_printf ("recalculating us");
	  LONGLONG now = get_clock (CLOCK_REALTIME)->usecs ();
	  if (now >= (start_time + us))
	    {
	      select_printf ("timed out after verification");
	      /* Set descriptor bits to zero per POSIX. */
	      UNIX_FD_ZERO (readfds, maxfds);
	      UNIX_FD_ZERO (writefds, maxfds);
	      UNIX_FD_ZERO (exceptfds, maxfds);
	      wait_state = select_stuff::select_ok;
	      ret = 0;
	    }
	  else
	    {
	      us -= (now - start_time);
	      start_time = now;
	      select_printf ("us now %D", us);
	    }
	}
    }
  while (wait_state == select_stuff::select_set_zero);

  if (wait_state < select_stuff::select_ok)
    ret = -1;
  return ret;
}

/* Call cleanup functions for all inspected fds.  Gets rid of any
   executing threads. */
void
select_stuff::cleanup ()
{
  select_record *s = &start;

  select_printf ("calling cleanup routines");
  while ((s = s->next))
    if (s->cleanup)
      {
	s->cleanup (s, this);
	s->cleanup = NULL;
      }
}

/* Destroy all storage associated with select stuff. */
inline void
select_stuff::destroy ()
{
  select_record *s;
  select_record *snext = start.next;

  select_printf ("deleting select records");
  while ((s = snext))
    {
      snext = s->next;
      delete s;
    }
  start.next = NULL;
}

select_stuff::~select_stuff ()
{
  cleanup ();
  destroy ();
}

#ifdef DEBUGGING
void
select_record::dump_select_record ()
{
  select_printf ("fd %d, h %p, fh %p, thread_errno %d, windows_handle %p",
		 fd, h, fh, thread_errno, windows_handle);
  select_printf ("read_ready %d, write_ready %d, except_ready %d",
		 read_ready, write_ready, except_ready);
  select_printf ("read_selected %d, write_selected %d, except_selected %d, except_on_write %d",
		 read_selected, write_selected, except_selected, except_on_write);

  select_printf ("startup %p, peek %p, verify %p cleanup %p, next %p",
		 startup, peek, verify, cleanup, next);
}
#endif /*DEBUGGING*/

/* Add a record to the select chain */
bool
select_stuff::test_and_set (int i, fd_set *readfds, fd_set *writefds,
			    fd_set *exceptfds)
{
  if (!UNIX_FD_ISSET (i, readfds) && !UNIX_FD_ISSET (i, writefds)
      && ! UNIX_FD_ISSET (i, exceptfds))
    return true;

  select_record *s = new select_record;
  if (!s)
    return false;

  s->next = start.next;
  start.next = s;

  if (UNIX_FD_ISSET (i, readfds) && !cygheap->fdtab.select_read (i, this))
    goto err;
  if (UNIX_FD_ISSET (i, writefds) && !cygheap->fdtab.select_write (i, this))
    goto err;
  if (UNIX_FD_ISSET (i, exceptfds) && !cygheap->fdtab.select_except (i, this))
    goto err; /* error */

  if (s->read_ready || s->write_ready || s->except_ready)
    always_ready = true;

  if (s->windows_handle)
    windows_used = true;

#ifdef DEBUGGING
  s->dump_select_record ();
#endif
  return true;

err:
  start.next = s->next;
  delete s;
  return false;
}

/* The heart of select.  Waits for an fd to do something interesting. */
select_stuff::wait_states
select_stuff::wait (fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
		    LONGLONG us)
{
  HANDLE w4[MAXIMUM_WAIT_OBJECTS];
  select_record *s = &start;
  DWORD m = 0, timer_idx = 0, cancel_idx = 0;

  /* Always wait for signals. */
  wait_signal_arrived here (w4[m++]);

  /* Set a timeout, or not, for WMFO. */
  DWORD wmfo_timeout = us ? INFINITE : 0;

  /* Optionally wait for pthread cancellation. */
  if ((w4[m] = pthread::get_cancel_event ()) != NULL)
    cancel_idx = m++;

  /* Loop through the select chain, starting up anything appropriate and
     counting the number of active fds. */
  DWORD startfds = m;
  while ((s = s->next))
    {
      /* Make sure to leave space for the timer, if we have a finite timeout. */
      if (m >= MAXIMUM_WAIT_OBJECTS - (us > 0LL ? 1 : 0))
	{
	  set_sig_errno (EINVAL);
	  return select_error;
	}
      if (!s->startup (s, this))
	{
	  s->set_select_errno ();
	  return select_error;
	}
      if (s->h != NULL)
	{
	  for (DWORD i = startfds; i < m; i++)
	    if (w4[i] == s->h)
	      goto next_while;
	  w4[m++] = s->h;
	}
next_while:;
    }

  /* Optionally create and set a waitable timer if a finite timeout has
     been requested.  Recycle cw_timer in the cygtls area so we only have
     to create the timer once per thread.  Since WFMO checks the handles
     in order, we append the timer as last object, otherwise it's preferred
     over actual events on the descriptors. */
  HANDLE &wait_timer = _my_tls.locals.cw_timer;
  if (us > 0LL)
    {
      NTSTATUS status;
      if (!wait_timer)
	{
	  status = NtCreateTimer (&wait_timer, TIMER_ALL_ACCESS, NULL,
				  NotificationTimer);
	  if (!NT_SUCCESS (status))
	    {
	      select_printf ("%y = NtCreateTimer ()\n", status);
	      return select_error;
	    }
	}
      LARGE_INTEGER ms_clock_ticks = { .QuadPart = -us * 10 };
      status = NtSetTimer (wait_timer, &ms_clock_ticks, NULL, NULL, FALSE,
			   0, NULL);
      if (!NT_SUCCESS (status))
	{
	  select_printf ("%y = NtSetTimer (%D)\n",
			 status, ms_clock_ticks.QuadPart);
	  return select_error;
	}
      w4[m] = wait_timer;
      timer_idx = m++;
    }

  debug_printf ("m %d, us %U, wmfo_timeout %d", m, us, wmfo_timeout);

  DWORD wait_ret;
  if (!windows_used)
    wait_ret = WaitForMultipleObjects (m, w4, FALSE, wmfo_timeout);
  else
    /* Using MWMO_INPUTAVAILABLE is the officially supported solution for
       the problem that the call to PeekMessage disarms the queue state
       so that a subsequent MWFMO hangs, even if there are still messages
       in the queue. */
    wait_ret = MsgWaitForMultipleObjectsEx (m, w4, wmfo_timeout,
					    QS_ALLINPUT | QS_ALLPOSTMESSAGE,
					    MWMO_INPUTAVAILABLE);
  select_printf ("wait_ret %d, m = %d.  verifying", wait_ret, m);

  if (timer_idx)
    {
      BOOLEAN current_state;
      NtCancelTimer (wait_timer, &current_state);
    }

  wait_states res;
  switch (wait_ret)
    {
    case WAIT_OBJECT_0:
      select_printf ("signal received");
      /* Need to get rid of everything when a signal occurs since we can't
	 be assured that a signal handler won't jump out of select entirely. */
      cleanup ();
      destroy ();
      /* select() is always interrupted by a signal so set EINTR,
	 unconditionally, ignoring any SA_RESTART detection by
	 call_signal_handler().  */
      _my_tls.call_signal_handler ();
      set_sig_errno (EINTR);
      res = select_signalled;	/* Cause loop exit in cygwin_select */
      break;
    case WAIT_FAILED:
      system_printf ("WaitForMultipleObjects failed, %E");
      s = &start;
      s->set_select_errno ();
      res = select_error;
      break;
    case WAIT_TIMEOUT:
was_timeout:
      select_printf ("timed out");
      res = select_set_zero;
      break;
    case WAIT_OBJECT_0 + 1:
      /* Cancel event? */
      if (wait_ret == cancel_idx)
	{
	  cleanup ();
	  destroy ();
	  pthread::static_cancel_self ();
	  /*NOTREACHED*/
	}
      fallthrough;
    default:
      /* Timer event? */
      if (wait_ret == timer_idx)
	goto was_timeout;

      s = &start;
      res = select_set_zero;
      /* Some types of objects (e.g., consoles) wake up on "inappropriate"
	 events like mouse movements.  The verify function will detect these
	 situations.  If it returns false, then this wakeup was a false alarm
	 and we should go back to waiting. */
      int ret = 0;
      while ((s = s->next))
	if (s->saw_error ())
	  {
	    set_errno (s->saw_error ());
	    res = select_error;		/* Somebody detected an error */
	    goto out;
	  }
	else if ((((wait_ret >= m && s->windows_handle)
	           || s->h == w4[wait_ret]))
		 && (ret = s->verify (s, readfds, writefds, exceptfds)) > 0)
	  res = select_ok;
	else if (ret < 0)
	  {
	    res = select_signalled;
	    goto out;
	  }

      select_printf ("res after verify %d", res);
      break;
    }
out:
  select_printf ("returning %d", res);
  return res;
}

static int
set_bits (select_record *me, fd_set *readfds, fd_set *writefds,
	  fd_set *exceptfds)
{
  int ready = 0;
  fhandler_socket_wsock *sock;
  select_printf ("me %p, testing fd %d (%s)", me, me->fd, me->fh->get_name ());
  if (me->read_selected && me->read_ready)
    {
      UNIX_FD_SET (me->fd, readfds);
      ready++;
    }
  if (me->write_selected && me->write_ready)
    {
      UNIX_FD_SET (me->fd, writefds);
      if (me->except_on_write && (sock = me->fh->is_wsock_socket ()))
	{
	  /* Set readfds entry in case of a failed connect. */
	  if (!me->read_ready && me->read_selected
	      && sock->connect_state () == connect_failed)
	    {
	      UNIX_FD_SET (me->fd, readfds);
	      ready++;
	    }
	}
      ready++;
    }
  if (me->except_selected && me->except_ready)
    {
      UNIX_FD_SET (me->fd, exceptfds);
      ready++;
    }
  select_printf ("ready %d", ready);
  return ready;
}

/* Poll every fd in the select chain.  Set appropriate fd in mask. */
int
select_stuff::poll (fd_set *readfds, fd_set *writefds, fd_set *exceptfds)
{
  int n = 0;
  select_record *s = &start;
  while ((s = s->next))
    {
      int ret = s->peek ? s->peek (s, true) : 1;
      if (ret < 0)
	return -1;
      n += (ret > 0) ?  set_bits (s, readfds, writefds, exceptfds) : 0;
    }
  return n;
}

static int
verify_true (select_record *, fd_set *, fd_set *, fd_set *)
{
  return 1;
}

static int
verify_ok (select_record *me, fd_set *readfds, fd_set *writefds,
	   fd_set *exceptfds)
{
  return set_bits (me, readfds, writefds, exceptfds);
}

static int
no_startup (select_record *, select_stuff *)
{
  return 1;
}

static int
no_verify (select_record *, fd_set *, fd_set *, fd_set *)
{
  return 0;
}

static int
pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
{
  if (fh->get_device () == FH_PIPER)
    {
      DWORD nbytes_in_pipe;
      if (!writing && PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
	return nbytes_in_pipe > 0;
      return -1;
    }

  IO_STATUS_BLOCK iosb = {{0}, 0};
  FILE_PIPE_LOCAL_INFORMATION fpli = {0};
  NTSTATUS status;

  status = NtQueryInformationFile (h, &iosb, &fpli, sizeof (fpli),
				   FilePipeLocalInformation);
  if (!NT_SUCCESS (status))
    {
      /* If NtQueryInformationFile fails, optimistically assume the
	 pipe is writable.  This could happen if we somehow
	 inherit a pipe that doesn't permit FILE_READ_ATTRIBUTES
	 access on the write end.  */
      select_printf ("fd %d, %s, NtQueryInformationFile failed, status %y",
		     fd, fh->get_name (), status);
      return writing ? 1 : -1;
    }
  if (writing)
    {
      /* If there is anything available in the pipe buffer then signal
        that.  This means that a pipe could still block since you could
        be trying to write more to the pipe than is available in the
        buffer but that is the hazard of select().

        Note that WriteQuotaAvailable is unreliable.

        Usually WriteQuotaAvailable on the write side reflects the space
        available in the inbound buffer on the read side.  However, if a
        pipe read is currently pending, WriteQuotaAvailable on the write side
        is decremented by the number of bytes the read side is requesting.
        So it's possible (even likely) that WriteQuotaAvailable is 0, even
        if the inbound buffer on the read side is not full.  This can lead to
        a deadlock situation: The reader is waiting for data, but select
        on the writer side assumes that no space is available in the read
        side inbound buffer.

        Consequentially, the only reliable information is available on the
        read side, so fetch info from the read side via the pipe-specific
        query handle.  Use fpli.WriteQuotaAvailable as storage for the actual
        interesting value, which is the InboundQuote on the write side,
        decremented by the number of bytes of data in that buffer. */
      /* Note: Do not use NtQueryInformationFile() for query_hdl because
	 NtQueryInformationFile() seems to interfere with reading pipes
	 in non-cygwin apps. Instead, use PeekNamedPipe() here. */
      if (fh->get_device () == FH_PIPEW && fpli.WriteQuotaAvailable == 0)
	{
	  HANDLE query_hdl = ((fhandler_pipe *) fh)->get_query_handle ();
	  if (!query_hdl)
	    query_hdl = ((fhandler_pipe *) fh)->temporary_query_hdl ();
	  if (!query_hdl)
	    return 1; /* We cannot know actual write pipe space. */
	  DWORD nbytes_in_pipe;
	  BOOL res =
	    PeekNamedPipe (query_hdl, NULL, 0, NULL, &nbytes_in_pipe, NULL);
	  if (!((fhandler_pipe *) fh)->get_query_handle ())
	    CloseHandle (query_hdl); /* Close temporary query_hdl */
	  if (!res)
	    return 1;
	  fpli.WriteQuotaAvailable = fpli.InboundQuota - nbytes_in_pipe;
	}
      if (fpli.WriteQuotaAvailable > 0)
	{
	  paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd,
			   fh->get_name (), fpli.InboundQuota,
			   fpli.WriteQuotaAvailable);
	  return 1;
	}
      /* TODO: Buffer really full or non-Cygwin reader? */
    }
  else if (fpli.ReadDataAvailable)
    {
      paranoid_printf ("fd %d, %s, read avail %u", fd, fh->get_name (),
		       fpli.ReadDataAvailable);
      return 1;
    }
  if (fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE)
    return -1;
  return 0;
}

static int
peek_pipe (select_record *s, bool from_select)
{
  HANDLE h;
  set_handle_or_return_if_not_open (h, s);

  int gotone = 0;
  fhandler_base *fh = (fhandler_base *) s->fh;

  DWORD dev = fh->get_device ();
  if (s->read_selected && dev != FH_PIPEW)
    {
      if (s->read_ready)
	{
	  select_printf ("%s, already ready for read", fh->get_name ());
	  gotone = 1;
	  goto out;
	}

      switch (fh->get_major ())
	{
	case DEV_PTYM_MAJOR:
	  {
	    fhandler_pty_master *fhm = (fhandler_pty_master *) fh;
	    fhm->flush_to_slave ();
	  }
	  break;
	default:
	  if (fh->get_readahead_valid ())
	    {
	      select_printf ("readahead");
	      gotone = s->read_ready = true;
	      goto out;
	    }
	}

      if (fh->bg_check (SIGTTIN, true) <= bg_eof)
	{
	  gotone = s->read_ready = true;
	  goto out;
	}
      int n = pipe_data_available (s->fd, fh, h, false);
      /* On PTY masters, check if input from the echo pipe is available. */
      if (n == 0 && fh->get_echo_handle ())
	n = pipe_data_available (s->fd, fh, fh->get_echo_handle (), false);

      if (n < 0)
	{
	  select_printf ("read: %s, n %d", fh->get_name (), n);
	  if (s->except_selected)
	    gotone += s->except_ready = true;
	  if (s->read_selected)
	    gotone += s->read_ready = true;
	}
      else if (n > 0)
	{
	  select_printf ("read: %s, ready for read: avail %d", fh->get_name (), n);
	  gotone += s->read_ready = true;
	}
      if (!gotone && s->fh->hit_eof ())
	{
	  select_printf ("read: %s, saw EOF", fh->get_name ());
	  if (s->except_selected)
	    gotone += s->except_ready = true;
	  if (s->read_selected)
	    gotone += s->read_ready = true;
	}
    }

out:
  if (fh->get_major () == DEV_PTYM_MAJOR)
    {
      fhandler_pty_master *fhm = (fhandler_pty_master *) fh;
      fhm->set_mask_flusho (s->read_ready);
    }
  h = fh->get_output_handle ();
  if (s->write_selected && dev != FH_PIPER)
    {
      if (dev == FH_PIPEW && ((fhandler_pipe *) fh)->reader_closed ())
	{
	  gotone += s->write_ready = true;
	  if (s->except_selected)
	    gotone += s->except_ready = true;
	  return gotone;
	}
      int n = pipe_data_available (s->fd, fh, h, true);
      select_printf ("write: %s, n %d", fh->get_name (), n);
      gotone += s->write_ready = n;
      if (n < 0 && s->except_selected)
	gotone += s->except_ready = true;
    }
  return gotone;
}

static int start_thread_pipe (select_record *me, select_stuff *stuff);

static DWORD
thread_pipe (void *arg)
{
  select_pipe_info *pi = (select_pipe_info *) arg;
  DWORD sleep_time = 0;
  bool looping = true;

  while (looping)
    {
      for (select_record *s = pi->start; (s = s->next); )
	if (s->startup == start_thread_pipe)
	  {
	    if (peek_pipe (s, true))
	      looping = false;
	    if (pi->stop_thread)
	      {
		select_printf ("stopping");
		looping = false;
		break;
	      }
	  }
      if (!looping)
	break;
      cygwait (pi->bye, sleep_time >> 3);
      if (sleep_time < 80)
	++sleep_time;
      if (pi->stop_thread)
	break;
    }
  return 0;
}

static int
start_thread_pipe (select_record *me, select_stuff *stuff)
{
  select_pipe_info *pi = stuff->device_specific_pipe;
  if (pi->start)
    me->h = *((select_pipe_info *) stuff->device_specific_pipe)->thread;
  else
    {
      pi->start = &stuff->start;
      pi->stop_thread = false;
      pi->bye = me->fh->get_select_sem ();
      if (pi->bye)
	DuplicateHandle (GetCurrentProcess (), pi->bye,
			 GetCurrentProcess (), &pi->bye,
			 0, 0, DUPLICATE_SAME_ACCESS);
      else
	pi->bye = CreateSemaphore (&sec_none_nih, 0, INT32_MAX, NULL);
      pi->thread = new cygthread (thread_pipe, pi, "pipesel");
      me->h = *pi->thread;
      if (!me->h)
	return 0;
    }
  return 1;
}

static void
pipe_cleanup (select_record *, select_stuff *stuff)
{
  select_pipe_info *pi = (select_pipe_info *) stuff->device_specific_pipe;
  if (!pi)
    return;
  if (pi->thread)
    {
      pi->stop_thread = true;
      ReleaseSemaphore (pi->bye, get_obj_handle_count (pi->bye), NULL);
      pi->thread->detach ();
      CloseHandle (pi->bye);
    }
  delete pi;
  stuff->device_specific_pipe = NULL;
}

select_record *
fhandler_pipe::select_read (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;

  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->read_selected = true;
  s->read_ready = false;
  return s;
}

select_record *
fhandler_pipe::select_write (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->write_selected = true;
  s->write_ready = false;
  return s;
}

select_record *
fhandler_pipe::select_except (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

static int
peek_fifo (select_record *s, bool from_select)
{
  if (cygheap->fdtab.not_open (s->fd))
    {
      s->thread_errno = EBADF;
      return -1;
    }

  int gotone = 0;
  fhandler_fifo *fh = (fhandler_fifo *) s->fh;

  if (s->read_selected)
    {
      if (s->read_ready)
	{
	  select_printf ("%s, already ready for read", fh->get_name ());
	  gotone = 1;
	  goto out;
	}

      if (fh->get_readahead_valid ())
	{
	  select_printf ("readahead");
	  gotone = s->read_ready = true;
	  goto out;
	}

      fh->reading_lock ();
      if (fh->take_ownership (1) < 0)
	{
	  fh->reading_unlock ();
	  goto out;
	}
      fh->fifo_client_lock ();
      int nconnected = 0;
      for (int i = 0; i < fh->get_nhandlers (); i++)
	{
	  fifo_client_handler &fc = fh->get_fc_handler (i);
	  fifo_client_connect_state prev_state = fc.query_and_set_state ();
	  if (fc.get_state () >= fc_connected)
	    {
	      nconnected++;
	      if (prev_state == fc_listening)
		/* The connection was not recorded by the fifo_reader_thread. */
		fh->record_connection (fc, false);
	      if (fc.get_state () == fc_input_avail)
		{
		  select_printf ("read: %s, ready for read", fh->get_name ());
		  fh->fifo_client_unlock ();
		  fh->reading_unlock ();
		  gotone += s->read_ready = true;
		  goto out;
		}
	    }
	}
      fh->fifo_client_unlock ();
      /* According to POSIX and the Linux man page, we're supposed to
	 report read ready if the FIFO is at EOF, i.e., if the pipe is
	 empty and there are no writers.  But there seems to be an
	 undocumented exception, observed on Linux and other platforms
	 (https://cygwin.com/pipermail/cygwin/2022-September/252223.html):
	 If no writer has ever been opened, then we do not report read
	 ready.  This can happen if a reader is opened with O_NONBLOCK
	 before any writers have opened.  To be consistent with other
	 platforms, we use a special EOF test that returns false if
	 there's never been a writer opened. */
      if (!nconnected && fh->select_hit_eof ())
	{
	  select_printf ("read: %s, saw EOF", fh->get_name ());
	  gotone += s->read_ready = true;
	  if (s->except_selected)
	    gotone += s->except_ready = true;
	}
      fh->reading_unlock ();
    }
out:
  if (s->write_selected)
    {
      int n = pipe_data_available (s->fd, fh, fh->get_handle (), true);
      select_printf ("write: %s, n %d", fh->get_name (), n);
      gotone += s->write_ready = n;
      if (n < 0 && s->except_selected)
	gotone += s->except_ready = true;
    }
  return gotone;
}

static int start_thread_fifo (select_record *me, select_stuff *stuff);

static DWORD
thread_fifo (void *arg)
{
  select_fifo_info *pi = (select_fifo_info *) arg;
  DWORD sleep_time = 0;
  bool looping = true;

  while (looping)
    {
      for (select_record *s = pi->start; (s = s->next); )
	if (s->startup == start_thread_fifo)
	  {
	    if (peek_fifo (s, true))
	      looping = false;
	    if (pi->stop_thread)
	      {
		select_printf ("stopping");
		looping = false;
		break;
	      }
	  }
      if (!looping)
	break;
      cygwait (pi->bye, sleep_time >> 3);
      if (sleep_time < 80)
	++sleep_time;
      if (pi->stop_thread)
	break;
    }
  return 0;
}

static int
start_thread_fifo (select_record *me, select_stuff *stuff)
{
  select_fifo_info *pi = stuff->device_specific_fifo;
  if (pi->start)
    me->h = *((select_fifo_info *) stuff->device_specific_fifo)->thread;
  else
    {
      pi->start = &stuff->start;
      pi->stop_thread = false;
      pi->bye = me->fh->get_select_sem ();
      if (pi->bye)
	DuplicateHandle (GetCurrentProcess (), pi->bye,
			 GetCurrentProcess (), &pi->bye,
			 0, 0, DUPLICATE_SAME_ACCESS);
      else
	pi->bye = CreateSemaphore (&sec_none_nih, 0, INT32_MAX, NULL);
      pi->thread = new cygthread (thread_fifo, pi, "fifosel");
      me->h = *pi->thread;
      if (!me->h)
	return 0;
    }
  return 1;
}

static void
fifo_cleanup (select_record *, select_stuff *stuff)
{
  select_fifo_info *pi = (select_fifo_info *) stuff->device_specific_fifo;
  if (!pi)
    return;
  if (pi->thread)
    {
      pi->stop_thread = true;
      ReleaseSemaphore (pi->bye, get_obj_handle_count (pi->bye), NULL);
      pi->thread->detach ();
      CloseHandle (pi->bye);
    }
  delete pi;
  stuff->device_specific_fifo = NULL;
}

select_record *
fhandler_fifo::select_read (select_stuff *ss)
{
  if (!ss->device_specific_fifo
      && (ss->device_specific_fifo = new select_fifo_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_fifo;
  s->peek = peek_fifo;
  s->verify = verify_ok;
  s->cleanup = fifo_cleanup;
  s->read_selected = true;
  s->read_ready = false;
  return s;
}

select_record *
fhandler_fifo::select_write (select_stuff *ss)
{
  if (!ss->device_specific_fifo
      && (ss->device_specific_fifo = new select_fifo_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_fifo;
  s->peek = peek_fifo;
  s->verify = verify_ok;
  s->cleanup = fifo_cleanup;
  s->write_selected = true;
  s->write_ready = false;
  return s;
}

select_record *
fhandler_fifo::select_except (select_stuff *ss)
{
  if (!ss->device_specific_fifo
      && (ss->device_specific_fifo = new select_fifo_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_fifo;
  s->peek = peek_fifo;
  s->verify = verify_ok;
  s->cleanup = fifo_cleanup;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

static int
peek_console (select_record *me, bool)
{
  fhandler_console *fh = (fhandler_console *) me->fh;

  if (!me->read_selected)
    return me->write_ready;

  if (fh->get_cons_readahead_valid ())
    return me->read_ready = true;

  if (fh->input_ready)
    return me->read_ready = true;

  if (me->read_ready)
    {
      select_printf ("already ready");
      return 1;
    }

  INPUT_RECORD irec;
  DWORD events_read;
  HANDLE h;
  set_handle_or_return_if_not_open (h, me);

  fh->acquire_input_mutex (mutex_timeout);
  while (!fh->input_ready && !fh->get_cons_readahead_valid ())
    {
      if (fh->bg_check (SIGTTIN, true) <= bg_eof)
	{
	  fh->release_input_mutex ();
	  return me->read_ready = true;
	}
      else
	{
	  acquire_attach_mutex (mutex_timeout);
	  DWORD resume_pid = fh->attach_console (fh->get_owner ());
	  BOOL r = PeekConsoleInputW (h, &irec, 1, &events_read);
	  fh->detach_console (resume_pid, fh->get_owner ());
	  release_attach_mutex ();
	  if (!r || !events_read)
	    break;
	}
      if (fhandler_console::input_winch == fh->process_input_message ()
	  && global_sigs[SIGWINCH].sa_handler != SIG_IGN
	  && global_sigs[SIGWINCH].sa_handler != SIG_DFL)
	{
	  set_sig_errno (EINTR);
	  fh->release_input_mutex ();
	  return -1;
	}
    }
  fh->release_input_mutex ();
  if (fh->input_ready || fh->get_cons_readahead_valid ())
    return me->read_ready = true;

  return me->write_ready;
}

static int
verify_console (select_record *me, fd_set *rfds, fd_set *wfds,
	      fd_set *efds)
{
  return peek_console (me, true);
}

static int console_startup (select_record *me, select_stuff *stuff);

static DWORD
thread_console (void *arg)
{
  select_console_info *ci = (select_console_info *) arg;
  DWORD sleep_time = 0;
  bool looping = true;

  while (looping)
    {
      for (select_record *s = ci->start; (s = s->next); )
	if (s->startup == console_startup)
	  {
	    if (peek_console (s, true))
	      looping = false;
	    if (ci->stop_thread)
	      {
		select_printf ("stopping");
		looping = false;
		break;
	      }
	  }
      if (!looping)
	break;
      cygwait (ci->bye, sleep_time >> 3);
      if (sleep_time < 80)
	++sleep_time;
      if (ci->stop_thread)
	break;
    }
  return 0;
}

static int
console_startup (select_record *me, select_stuff *stuff)
{
  select_console_info *ci = stuff->device_specific_console;
  if (ci->start)
    me->h = *(stuff->device_specific_console)->thread;
  else
    {
      ci->start = &stuff->start;
      ci->stop_thread = false;
      ci->bye = CreateEvent (&sec_none_nih, TRUE, FALSE, NULL);
      ci->thread = new cygthread (thread_console, ci, "conssel");
      me->h = *ci->thread;
      if (!me->h)
	return 0;
    }
  return 1;
}

static void
console_cleanup (select_record *me, select_stuff *stuff)
{
  select_console_info *ci = stuff->device_specific_console;
  if (!ci)
    return;
  if (ci->thread)
    {
      ci->stop_thread = true;
      SetEvent (ci->bye);
      ci->thread->detach ();
      CloseHandle (ci->bye);
    }
  delete ci;
  stuff->device_specific_console = NULL;
}

select_record *
fhandler_console::select_read (select_stuff *ss)
{
  if (!ss->device_specific_console
      && (ss->device_specific_console = new select_console_info) == NULL)
    return NULL;

  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = console_startup;
      s->verify = verify_console;
      set_cursor_maybe ();
    }

  s->peek = peek_console;
  s->read_selected = true;
  s->read_ready = input_ready || get_cons_readahead_valid ();
  s->cleanup = console_cleanup;
  return s;
}

select_record *
fhandler_console::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
      set_cursor_maybe ();
    }

  s->peek = peek_console;
  s->write_selected = true;
  s->write_ready = true;
  return s;
}

select_record *
fhandler_console::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
      set_cursor_maybe ();
    }

  s->peek = peek_console;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

select_record *
fhandler_pty_common::select_read (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;

  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->read_selected = true;
  s->read_ready = false;
  return s;
}

select_record *
fhandler_pty_common::select_write (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->write_selected = true;
  s->write_ready = false;
  return s;
}

select_record *
fhandler_pty_common::select_except (select_stuff *ss)
{
  if (!ss->device_specific_pipe
      && (ss->device_specific_pipe = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = start_thread_pipe;
  s->peek = peek_pipe;
  s->verify = verify_ok;
  s->cleanup = pipe_cleanup;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

static int
verify_tty_slave (select_record *me, fd_set *readfds, fd_set *writefds,
	   fd_set *exceptfds)
{
  fhandler_pty_slave *ptys = (fhandler_pty_slave *) me->fh;
  if (me->read_selected && IsEventSignalled (ptys->input_available_event))
    me->read_ready = true;
  return set_bits (me, readfds, writefds, exceptfds);
}

static int
peek_pty_slave (select_record *s, bool from_select)
{
  int gotone = 0;
  fhandler_base *fh = (fhandler_base *) s->fh;
  fhandler_pty_slave *ptys = (fhandler_pty_slave *) fh;

  if (s->read_selected)
    {
      if (s->read_ready)
	{
	  select_printf ("%s, already ready for read", fh->get_name ());
	  gotone = 1;
	  goto out;
	}

      if (fh->bg_check (SIGTTIN, true) <= bg_eof)
	{
	  gotone = s->read_ready = true;
	  goto out;
	}

      if (IsEventSignalled (ptys->input_available_event))
	{
	  gotone = s->read_ready = true;
	  goto out;
	}

      if (!gotone && s->fh->hit_eof ())
	{
	  select_printf ("read: %s, saw EOF", fh->get_name ());
	  if (s->except_selected)
	    gotone += s->except_ready = true;
	  if (s->read_selected)
	    gotone += s->read_ready = true;
	}
    }

out:
  HANDLE h = ptys->get_output_handle ();
  if (s->write_selected)
    {
      int n = pipe_data_available (s->fd, fh, h, true);
      select_printf ("write: %s, n %d", fh->get_name (), n);
      gotone += s->write_ready = n;
      if (n < 0 && s->except_selected)
	gotone += s->except_ready = true;
    }
  return gotone;
}

static int pty_slave_startup (select_record *me, select_stuff *stuff);

static DWORD
thread_pty_slave (void *arg)
{
  select_pipe_info *pi = (select_pipe_info *) arg;
  DWORD sleep_time = 0;
  bool looping = true;

  while (looping)
    {
      for (select_record *s = pi->start; (s = s->next); )
	if (s->startup == pty_slave_startup)
	  {
	    if (peek_pty_slave (s, true))
	      looping = false;
	    if (pi->stop_thread)
	      {
		select_printf ("stopping");
		looping = false;
		break;
	      }
	  }
      if (!looping)
	break;
      cygwait (pi->bye, sleep_time >> 3);
      if (sleep_time < 80)
	++sleep_time;
      if (pi->stop_thread)
	break;
    }
  return 0;
}

static int
pty_slave_startup (select_record *me, select_stuff *stuff)
{
  fhandler_base *fh = (fhandler_base *) me->fh;
  fhandler_pty_slave *ptys = (fhandler_pty_slave *) fh;
  if (me->read_selected)
    ptys->mask_switch_to_nat_pipe (true, true);

  select_pipe_info *pi = stuff->device_specific_ptys;
  if (pi->start)
    me->h = *((select_pipe_info *) stuff->device_specific_ptys)->thread;
  else
    {
      pi->start = &stuff->start;
      pi->stop_thread = false;
      pi->bye = CreateEvent (&sec_none_nih, TRUE, FALSE, NULL);
      pi->thread = new cygthread (thread_pty_slave, pi, "ptyssel");
      me->h = *pi->thread;
      if (!me->h)
	return 0;
    }
  return 1;
}

static void
pty_slave_cleanup (select_record *me, select_stuff *stuff)
{
  fhandler_base *fh = (fhandler_base *) me->fh;
  fhandler_pty_slave *ptys = (fhandler_pty_slave *) fh;
  select_pipe_info *pi = (select_pipe_info *) stuff->device_specific_ptys;
  if (!pi)
    return;
  if (me->read_selected && pi->start)
    ptys->mask_switch_to_nat_pipe (false, false);
  if (pi->thread)
    {
      pi->stop_thread = true;
      SetEvent (pi->bye);
      pi->thread->detach ();
      CloseHandle (pi->bye);
    }
  delete pi;
  stuff->device_specific_ptys = NULL;
}

select_record *
fhandler_pty_slave::select_read (select_stuff *ss)
{
  if (!ss->device_specific_ptys
      && (ss->device_specific_ptys = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = pty_slave_startup;
  s->peek = peek_pty_slave;
  s->verify = verify_tty_slave;
  s->read_selected = true;
  s->read_ready = false;
  s->cleanup = pty_slave_cleanup;
  return s;
}

select_record *
fhandler_pty_slave::select_write (select_stuff *ss)
{
  if (!ss->device_specific_ptys
      && (ss->device_specific_ptys = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = pty_slave_startup;
  s->peek = peek_pty_slave;
  s->verify = verify_tty_slave;
  s->write_selected = true;
  s->write_ready = false;
  s->cleanup = pty_slave_cleanup;
  return s;
}

select_record *
fhandler_pty_slave::select_except (select_stuff *ss)
{
  if (!ss->device_specific_ptys
      && (ss->device_specific_ptys = new select_pipe_info) == NULL)
    return NULL;
  select_record *s = ss->start.next;
  s->startup = pty_slave_startup;
  s->peek = peek_pty_slave;
  s->verify = verify_tty_slave;
  s->except_selected = true;
  s->except_ready = false;
  s->cleanup = pty_slave_cleanup;
  return s;
}

select_record *
fhandler_dev_null::select_read (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->h = get_handle ();
  s->read_selected = true;
  s->read_ready = true;
  return s;
}

select_record *
fhandler_dev_null::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->h = get_handle ();
  s->write_selected = true;
  s->write_ready = true;
  return s;
}

select_record *
fhandler_dev_null::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->h = get_handle ();
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

static int
peek_serial (select_record *s, bool)
{
  HANDLE h;
  COMSTAT st;
  DWORD io_err;

  fhandler_serial *fh = (fhandler_serial *) s->fh;

  set_handle_or_return_if_not_open (h, s);

  if ((s->read_selected && s->read_ready)
      || (s->write_selected && s->write_ready))
    {
      select_printf ("already ready");
      return true;
    }

  if (fh->get_readahead_valid ())
    return s->read_ready = true;

  if (!ClearCommError (h, &io_err, &st))
    {
      select_printf ("ClearCommError %E");
      goto err;
    }
  if (st.cbInQue)
    return s->read_ready = true;

  return 0;

err:
  if (GetLastError () == ERROR_OPERATION_ABORTED)
    {
      select_printf ("operation aborted");
      return false;
    }

  s->set_select_errno ();
  return -1;
}

static void
serial_read_cleanup (select_record *s, select_stuff *stuff)
{
  if (s->h)
    {
      HANDLE h = ((fhandler_serial *) s->fh)->get_handle ();
      DWORD undefined;

      if (h)
	{
	  CancelIo (h);
	  GetOverlappedResult (h, &s->fh_data_serial->ov, &undefined, TRUE);
	}
      CloseHandle (s->fh_data_serial->ov.hEvent);
      delete s->fh_data_serial;
    }
}

static int
verify_serial (select_record *me, fd_set *rfds, fd_set *wfds, fd_set *efds)
{
  return peek_serial (me, true);
}

select_record *
fhandler_serial::select_read (select_stuff *ss)
{
  COMSTAT st;
  DWORD io_err;

  select_record *s = ss->start.next;

  s->startup = no_startup;
  s->verify = verify_serial;
  s->cleanup = serial_read_cleanup;
  s->peek = peek_serial;
  s->read_selected = true;
  s->read_ready = false;

  s->fh_data_serial = new (fh_select_data_serial);
  s->fh_data_serial->ov.hEvent = CreateEvent (&sec_none_nih, TRUE, FALSE, NULL);

  /* This is apparently necessary for the com0com driver.
     See: http://cygwin.com/ml/cygwin/2009-01/msg00667.html */
  SetCommMask (get_handle (), 0);
  SetCommMask (get_handle (), EV_RXCHAR);
  if (ClearCommError (get_handle (), &io_err, &st) && st.cbInQue)
    s->read_ready = true;
  else if (WaitCommEvent (get_handle (), &s->fh_data_serial->event,
			  &s->fh_data_serial->ov))
    s->read_ready = true;
  else if (GetLastError () == ERROR_IO_PENDING)
    s->h = s->fh_data_serial->ov.hEvent;
  else
    select_printf ("WaitCommEvent %E");

  /* No overlapped operation?  Destroy the helper struct */
  if (!s->h)
    {
      CloseHandle (s->fh_data_serial->ov.hEvent);
      delete s->fh_data_serial;
    }
  return s;
}

select_record *
fhandler_serial::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;

  s->startup = no_startup;
  s->verify = verify_serial;
  s->peek = peek_serial;
  s->write_selected = true;
  s->write_ready = true;
  return s;
}

select_record *
fhandler_serial::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;

  s->startup = no_startup;
  s->verify = verify_serial;
  s->peek = peek_serial;
  s->except_selected = false;	// Can't do this
  s->except_ready = false;
  return s;
}

select_record *
fhandler_base::select_read (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = get_handle ();
  s->read_selected = true;
  s->read_ready = true;
  return s;
}

select_record *
fhandler_base::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = get_output_handle ();
  s->write_selected = true;
  s->write_ready = true;
  return s;
}

select_record *
fhandler_base::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = NULL;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

static int
peek_socket (select_record *me, bool)
{
  fhandler_socket_wsock *fh = (fhandler_socket_wsock *) me->fh;
  long events;
  /* Don't play with the settings again, unless having taken a deep look into
     Richard W. Stevens Network Programming book and how these flags are
     defined in Winsock.  Thank you. */
  long evt_mask = (me->read_selected ? (FD_READ | FD_ACCEPT | FD_CLOSE) : 0)
		| (me->write_selected ? (FD_WRITE | FD_CONNECT | FD_CLOSE) : 0)
		| (me->except_selected ? FD_OOB : 0);
  int ret = fh->evaluate_events (evt_mask, events, false);
  if (me->read_selected)
    me->read_ready |= ret || !!(events & (FD_READ | FD_ACCEPT | FD_CLOSE));
  if (me->write_selected)
    /* Don't check for FD_CLOSE here.  Only an error case (ret == -1)
       will set ready for writing. */
    me->write_ready |= ret || !!(events & (FD_WRITE | FD_CONNECT));
  if (me->except_selected)
    me->except_ready |= !!(events & FD_OOB);

  select_printf ("read_ready: %d, write_ready: %d, except_ready: %d",
		 me->read_ready, me->write_ready, me->except_ready);
  return me->read_ready || me->write_ready || me->except_ready;
}

static int start_thread_socket (select_record *, select_stuff *);

static DWORD
thread_socket (void *arg)
{
  select_socket_info *si = (select_socket_info *) arg;
  DWORD timeout = (si->num_w4 <= MAXIMUM_WAIT_OBJECTS)
		  ? INFINITE
		  : (64 / (roundup2 (si->num_w4, MAXIMUM_WAIT_OBJECTS)
			   / MAXIMUM_WAIT_OBJECTS));
  bool event = false;

  select_printf ("stuff_start %p, timeout %u", si->start, timeout);
  while (!event)
    {
      for (select_record *s = si->start; (s = s->next); )
	if (s->startup == start_thread_socket)
	  if (peek_socket (s, false))
	    event = true;
      if (!event)
	for (int i = 0; i < si->num_w4; i += MAXIMUM_WAIT_OBJECTS)
	  switch (WaitForMultipleObjects (MIN (si->num_w4 - i,
					       MAXIMUM_WAIT_OBJECTS),
					  si->w4 + i, FALSE, timeout))
	    {
	    case WAIT_FAILED:
	      goto out;
	    case WAIT_TIMEOUT:
	      continue;
	    case WAIT_OBJECT_0:
	      if (!i)	/* Socket event set. */
		goto out;
	      fallthrough;
	    default:
	      break;
	    }
    }
out:
  select_printf ("leaving thread_socket");
  return 0;
}

static inline bool init_tls_select_info () __attribute__ ((always_inline));
static inline bool
init_tls_select_info ()
{
  if (!_my_tls.locals.select.sockevt)
    {
      _my_tls.locals.select.sockevt = CreateEvent (&sec_none_nih, TRUE, FALSE,
						   NULL);
      if (!_my_tls.locals.select.sockevt)
	return false;
    }
  if (!_my_tls.locals.select.ser_num)
    {
      _my_tls.locals.select.ser_num
	      = (LONG *) malloc (MAXIMUM_WAIT_OBJECTS * sizeof (LONG));
      if (!_my_tls.locals.select.ser_num)
	return false;
      _my_tls.locals.select.w4
	      = (HANDLE *) malloc (MAXIMUM_WAIT_OBJECTS * sizeof (HANDLE));
      if (!_my_tls.locals.select.w4)
	{
	  free (_my_tls.locals.select.ser_num);
	  _my_tls.locals.select.ser_num = NULL;
	  return false;
	}
      _my_tls.locals.select.max_w4 = MAXIMUM_WAIT_OBJECTS;
    }
  return true;
}

static int
start_thread_socket (select_record *me, select_stuff *stuff)
{
  select_socket_info *si;

  if ((si = (select_socket_info *) stuff->device_specific_socket))
    {
      me->h = *si->thread;
      return 1;
    }

  si = new select_socket_info;

  if (!init_tls_select_info ())
    {
      delete si;
      return 0;
    }

  si->ser_num = _my_tls.locals.select.ser_num;
  si->w4 = _my_tls.locals.select.w4;

  si->w4[0] = _my_tls.locals.select.sockevt;
  si->num_w4 = 1;

  select_record *s = &stuff->start;
  while ((s = s->next))
    if (s->startup == start_thread_socket)
      {
	/* No event/socket should show up multiple times.  Every socket
	   is uniquely identified by its serial number in the global
	   wsock_events record. */
	const LONG ser_num = ((fhandler_socket_wsock *) s->fh)->serial_number ();
	for (int i = 1; i < si->num_w4; ++i)
	  if (si->ser_num[i] == ser_num)
	    goto continue_outer_loop;
	if (si->num_w4 >= _my_tls.locals.select.max_w4)
	  {
	    LONG *nser = (LONG *) realloc (si->ser_num,
					   (_my_tls.locals.select.max_w4
					    + MAXIMUM_WAIT_OBJECTS)
					   * sizeof (LONG));
	    if (!nser)
	      {
		delete si;
		return 0;
	      }
	    _my_tls.locals.select.ser_num = si->ser_num = nser;
	    HANDLE *nw4 = (HANDLE *) realloc (si->w4,
					   (_my_tls.locals.select.max_w4
					    + MAXIMUM_WAIT_OBJECTS)
					   * sizeof (HANDLE));
	    if (!nw4)
	      {
		delete si;
		return 0;
	      }
	    _my_tls.locals.select.w4 = si->w4 = nw4;
	    _my_tls.locals.select.max_w4 += MAXIMUM_WAIT_OBJECTS;
	  }
	si->ser_num[si->num_w4] = ser_num;
	si->w4[si->num_w4++] = ((fhandler_socket_wsock *) s->fh)->wsock_event ();
      continue_outer_loop:
	;
      }
  stuff->device_specific_socket = si;
  si->start = &stuff->start;
  select_printf ("stuff_start %p", &stuff->start);
  si->thread = new cygthread (thread_socket, si, "socksel");
  me->h = *si->thread;
  return 1;
}

void
socket_cleanup (select_record *, select_stuff *stuff)
{
  select_socket_info *si = (select_socket_info *) stuff->device_specific_socket;
  select_printf ("si %p si->thread %p", si, si ? si->thread : NULL);
  if (!si)
    return;
  if (si->thread)
    {
      SetEvent (si->w4[0]);
      /* Wait for thread to go away */
      si->thread->detach ();
      ResetEvent (si->w4[0]);
    }
  delete si;
  stuff->device_specific_socket = NULL;
  select_printf ("returning");
}

select_record *
fhandler_socket_wsock::select_read (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = start_thread_socket;
      s->verify = verify_true;
      s->cleanup = socket_cleanup;
    }
  s->peek = peek_socket;
  s->read_ready = saw_shutdown_read ();
  s->read_selected = true;
  return s;
}

select_record *
fhandler_socket_wsock::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = start_thread_socket;
      s->verify = verify_true;
      s->cleanup = socket_cleanup;
    }
  s->peek = peek_socket;
  s->write_ready = saw_shutdown_write () || connect_state () == unconnected;
  s->write_selected = true;
  if (connect_state () != unconnected)
    s->except_on_write = true;
  return s;
}

select_record *
fhandler_socket_wsock::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = start_thread_socket;
      s->verify = verify_true;
      s->cleanup = socket_cleanup;
    }
  s->peek = peek_socket;
  s->except_selected = true;
  return s;
}

#ifdef __WITH_AF_UNIX

select_record *
fhandler_socket_unix::select_read (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = get_handle ();
  s->read_selected = true;
  s->read_ready = true;
  return s;
}

select_record *
fhandler_socket_unix::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = get_handle ();
  s->write_selected = true;
  s->write_ready = true;
  return s;
}

select_record *
fhandler_socket_unix::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->h = NULL;
  s->except_selected = true;
  s->except_ready = false;
  return s;
}

#endif /* __WITH_AF_UNIX */

static int
peek_windows (select_record *me, bool)
{
  MSG m;
  HANDLE h;
  set_handle_or_return_if_not_open (h, me);
  /* We need the hWnd value, not the io_handle. */
  h = ((fhandler_windows *) me->fh)->get_hwnd ();

  if (me->read_selected && me->read_ready)
    return 1;

  if (PeekMessageW (&m, (HWND) h, 0, 0, PM_NOREMOVE))
    {
      me->read_ready = true;
      select_printf ("window %d(%p) ready", me->fd, h);
      return 1;
    }

  select_printf ("window %d(%p) not ready", me->fd, h);
  return me->write_ready;
}

static int
verify_windows (select_record *me, fd_set *rfds, fd_set *wfds,
		fd_set *efds)
{
  return peek_windows (me, true);
}

select_record *
fhandler_windows::select_read (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
    }
  s->verify = verify_windows;
  s->peek = peek_windows;
  s->read_selected = true;
  s->read_ready = false;
  s->windows_handle = true;
  return s;
}

select_record *
fhandler_windows::select_write (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->peek = peek_windows;
  s->write_selected = true;
  s->write_ready = true;
  s->windows_handle = true;
  return s;
}

select_record *
fhandler_windows::select_except (select_stuff *ss)
{
  select_record *s = ss->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_ok;
    }
  s->peek = peek_windows;
  s->except_selected = true;
  s->except_ready = false;
  s->windows_handle = true;
  return s;
}

static int
peek_signalfd (select_record *me, bool)
{
  if (((fhandler_signalfd *) me->fh)->poll () == 0)
    {
      select_printf ("signalfd %d ready", me->fd);
      me->read_ready = true;
      return 1;
    }
  select_printf ("signalfd %d not ready", me->fd);
  return 0;
}

static int
verify_signalfd (select_record *me, fd_set *rfds, fd_set *wfds, fd_set *efds)
{
  return peek_signalfd (me, true);
}

extern HANDLE my_pendingsigs_evt;

select_record *
fhandler_signalfd::select_read (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_signalfd;
    }
  s->peek = peek_signalfd;
  s->h = my_pendingsigs_evt;	/* wait_sig sets this if signal are pending */
  s->read_selected = true;
  s->read_ready = false;
  return s;
}

select_record *
fhandler_signalfd::select_write (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->peek = NULL;
  s->write_selected = false;
  s->write_ready = false;
  return s;
}

select_record *
fhandler_signalfd::select_except (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->peek = NULL;
  s->except_selected = false;
  s->except_ready = false;
  return s;
}

static int
peek_timerfd (select_record *me, bool)
{
  if (WaitForSingleObject (me->h, 0) == WAIT_OBJECT_0)
    {
      select_printf ("timerfd %d ready", me->fd);
      me->read_ready = true;
      return 1;
    }
  select_printf ("timerfd %d not ready", me->fd);
  return 0;
}

static int
verify_timerfd (select_record *me, fd_set *rfds, fd_set *wfds,
		fd_set *efds)
{
  return peek_timerfd (me, true);
}

select_record *
fhandler_timerfd::select_read (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = verify_timerfd;
    }
  s->h = get_timerfd_handle ();
  s->peek = peek_timerfd;
  s->read_selected = true;
  s->read_ready = false;
  return s;
}

select_record *
fhandler_timerfd::select_write (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->peek = NULL;
  s->write_selected = false;
  s->write_ready = false;
  return s;
}

select_record *
fhandler_timerfd::select_except (select_stuff *stuff)
{
  select_record *s = stuff->start.next;
  if (!s->startup)
    {
      s->startup = no_startup;
      s->verify = no_verify;
    }
  s->peek = NULL;
  s->except_selected = false;
  s->except_ready = false;
  return s;
}