guile/libguile/poll.c

/* Copyright 2010,2013,2018,2025
     Free Software Foundation, Inc.

   This file is part of Guile.

   Guile is free software: you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published
   by the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   Guile is distributed in the hope that it will be useful, but WITHOUT
   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
   License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with Guile.  If not, see
   <https://www.gnu.org/licenses/>.  */




#define _GNU_SOURCE

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <errno.h>
#include <poll.h>

#include "async.h"
#include "bytevectors.h"
#include "error.h"
#include "extensions.h"
#include "gsubr.h"
#include "modules.h"
#include "numbers.h"
#include "ports-internal.h"
#include "syscalls.h"
#include "vectors.h"
#include "version.h"

#include "poll.h"




/* {Poll}
 */

/* Poll a set of file descriptors, waiting until one or more of them is
   ready to perform input or output.

   This is a low-level interface.  See the `(ice-9 poll)' module for a more
   usable wrapper.

   `pollfds' is expected to be a bytevector, laid out in contiguous blocks of 64
   bits.  Each block has the format of one `struct pollfd': a 32-bit int file
   descriptor, a 16-bit int events mask, and a 16-bit int revents mask.

   The number of pollfd structures in `pollfds' is specified in
   `nfds'. `pollfds' must be at least long enough to support that number of
   structures. It may be longer, in which case the trailing entries are left
   untouched.

   The pollfds bytevector is modified directly, setting the returned events in
   the final two bytes (the revents member).

   Since Scheme ports can buffer input or output in userspace, a Scheme
   poll interface needs to take that into account as well.  The `ports'
   argument, a vector big enough for `nfds' elements, is given for this
   purpose.  If a pollfd entry has a corresponding open port, that port
   is scanned for available input or output before dropping into the
   poll.  If any port has buffered I/O available, the poll syscall is
   still issued, but with a timeout of 0 milliseconds, and a full port
   scan occurs after the poll returns.

   If timeout is given and is non-negative, the poll will return after that
   number of milliseconds if no fd became active.
   */
static SCM
scm_primitive_poll (SCM pollfds, SCM nfds, SCM ports, SCM timeout)
#define FUNC_NAME "primitive-poll"
{
  int rv = 0;
  nfds_t i;
  nfds_t c_nfds;
  int c_timeout;
  int have_buffered_io = 0;
  struct pollfd *fds;

  SCM_VALIDATE_BYTEVECTOR (SCM_ARG1, pollfds);
  c_nfds = scm_to_uint32 (nfds);
  c_timeout = scm_to_int (timeout);
  
  if (SCM_UNLIKELY (SCM_BYTEVECTOR_LENGTH (pollfds)
                    < c_nfds * sizeof(struct pollfd)))
    SCM_OUT_OF_RANGE (SCM_ARG2, nfds);
  
  SCM_VALIDATE_VECTOR (SCM_ARG3, ports);
  if (SCM_UNLIKELY (scm_c_vector_length (ports) < c_nfds))
    SCM_OUT_OF_RANGE (SCM_ARG3, ports);
    
  fds = (struct pollfd*)SCM_BYTEVECTOR_CONTENTS (pollfds);
  
  for (i = 0; i < c_nfds; i++)
    {
      SCM port = scm_c_vector_ref (ports, i);
      short int revents = 0;

      if (SCM_PORTP (port))
        {
          if (SCM_CLOSEDP (port))
            revents |= POLLERR;
          else
            {
              scm_t_port *pt = SCM_PORT (port);
              size_t tmp;

              if (scm_port_buffer_can_take (pt->read_buf, &tmp) > 0)
                /* Buffered input waiting to be read. */
                revents |= POLLIN;
              if (SCM_OUTPUT_PORT_P (port)
                  && scm_port_buffer_can_put (pt->write_buf, &tmp) > 1)
                /* Buffered output possible.  The "> 1" is because
                   writing the last byte would flush the port.  */
                revents |= POLLOUT;
            }
        }

      if (revents & fds[i].events)
        {
          have_buffered_io = 1;
          c_timeout = 0;
          break;
        }
    }

  SCM_SYSCALL (rv = poll (fds, c_nfds, c_timeout));

  if (rv == -1)
    SCM_SYSERROR;

  if (have_buffered_io)
    for (i = 0; i < c_nfds; i++)
      {
        SCM port = scm_c_vector_ref (ports, i);
        short int revents = 0;

        if (SCM_PORTP (port))
          {
            if (SCM_CLOSEDP (port))
              revents |= POLLERR;
            else
              {
                scm_t_port *pt = SCM_PORT (port);
                size_t tmp;

                if (scm_port_buffer_can_take (pt->read_buf, &tmp) > 0)
                  /* Buffered input waiting to be read. */
                  revents |= POLLIN;
                if (SCM_OUTPUT_PORT_P (port)
                    && scm_port_buffer_can_put (pt->write_buf, &tmp) > 1)
                  /* Buffered output possible.  The "> 1" is because
                     writing the last byte would flush the port.  */
                  revents |= POLLOUT;
              }
          }

        /* Mask in the events we are interested, and test if any are
           interesting. */
        if ((revents &= fds[i].events))
          {
            /* Could be the underlying fd is also ready for reading.  */
            if (!fds[i].revents)
              rv++;

            /* In any case, add these events to whatever the syscall
               set. */
            fds[i].revents |= revents;
          }
      }

  return scm_from_int (rv);
}
#undef FUNC_NAME




static void
scm_init_poll (void)
{
  scm_c_define_gsubr ("primitive-poll", 4, 0, 0,
                      SCM_AS_SUBR (scm_primitive_poll));
  scm_c_define ("%sizeof-struct-pollfd", scm_from_size_t (sizeof (struct pollfd)));

#ifdef POLLIN
  scm_c_define ("POLLIN", scm_from_int (POLLIN));
#endif 	       
#ifdef POLLPRI
  scm_c_define ("POLLPRI", scm_from_int (POLLPRI));
#endif 	       
#ifdef POLLOUT
  scm_c_define ("POLLOUT", scm_from_int (POLLOUT));
#endif 	       
#ifdef POLLRDHUP
  scm_c_define ("POLLRDHUP", scm_from_int (POLLRDHUP));
#endif 	       
#ifdef POLLERR
  scm_c_define ("POLLERR", scm_from_int (POLLERR));
#endif 	       
#ifdef POLLHUP
  scm_c_define ("POLLHUP", scm_from_int (POLLHUP));
#endif 	       
#ifdef POLLNVAL
  scm_c_define ("POLLNVAL", scm_from_int (POLLNVAL));
#endif 	       

}

void
scm_register_poll (void)
{
  scm_c_register_extension ("libguile-" SCM_EFFECTIVE_VERSION,
                            "scm_init_poll",
			    (scm_t_extension_init_func) scm_init_poll,
			    NULL);
}