source: vendor/3.5.0/lib/tevent/tevent_select.c

/* 
   Unix SMB/CIFS implementation.
   main select loop and event handling
   Copyright (C) Andrew Tridgell        2003-2005
   Copyright (C) Stefan Metzmacher      2005-2009

     ** NOTE! The following LGPL license applies to the tevent
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL

   This library 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.

   This library 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 this library; if not, see <http://www.gnu.org/licenses/>.
*/

#include "replace.h"
#include "system/filesys.h"
#include "system/select.h"
#include "tevent.h"
#include "tevent_util.h"
#include "tevent_internal.h"

struct select_event_context {
        /* a pointer back to the generic event_context */
        struct tevent_context *ev;

        /* the maximum file descriptor number in fd_events */
        int maxfd;

        /* information for exiting from the event loop */
        int exit_code;
};

/*
  create a select_event_context structure.
*/
static int select_event_context_init(struct tevent_context *ev)
{
        struct select_event_context *select_ev;

        select_ev = talloc_zero(ev, struct select_event_context);
        if (!select_ev) return -1;
        select_ev->ev = ev;

        ev->additional_data = select_ev;
        return 0;
}

/*
  recalculate the maxfd
*/
static void calc_maxfd(struct select_event_context *select_ev)
{
        struct tevent_fd *fde;

        select_ev->maxfd = 0;
        for (fde = select_ev->ev->fd_events; fde; fde = fde->next) {
                if (fde->fd > select_ev->maxfd) {
                        select_ev->maxfd = fde->fd;
                }
        }
}


/* to mark the ev->maxfd invalid
 * this means we need to recalculate it
 */
#define EVENT_INVALID_MAXFD (-1)

/*
  destroy an fd_event
*/
static int select_event_fd_destructor(struct tevent_fd *fde)
{
        struct tevent_context *ev = fde->event_ctx;
        struct select_event_context *select_ev = NULL;

        if (ev) {
                select_ev = talloc_get_type(ev->additional_data,
                                            struct select_event_context);

                if (select_ev->maxfd == fde->fd) {
                        select_ev->maxfd = EVENT_INVALID_MAXFD;
                }
        }

        return tevent_common_fd_destructor(fde);
}

/*
  add a fd based event
  return NULL on failure (memory allocation error)
*/
static struct tevent_fd *select_event_add_fd(struct tevent_context *ev, TALLOC_CTX *mem_ctx,
                                             int fd, uint16_t flags,
                                             tevent_fd_handler_t handler,
                                             void *private_data,
                                             const char *handler_name,
                                             const char *location)
{
        struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
                                                           struct select_event_context);
        struct tevent_fd *fde;

        fde = tevent_common_add_fd(ev, mem_ctx, fd, flags,
                                   handler, private_data,
                                   handler_name, location);
        if (!fde) return NULL;

        if (fde->fd > select_ev->maxfd) {
                select_ev->maxfd = fde->fd;
        }
        talloc_set_destructor(fde, select_event_fd_destructor);

        return fde;
}

/*
  event loop handling using select()
*/
static int select_event_loop_select(struct select_event_context *select_ev, struct timeval *tvalp)
{
        fd_set r_fds, w_fds;
        struct tevent_fd *fde;
        int selrtn;

        /* we maybe need to recalculate the maxfd */
        if (select_ev->maxfd == EVENT_INVALID_MAXFD) {
                calc_maxfd(select_ev);
        }

        FD_ZERO(&r_fds);
        FD_ZERO(&w_fds);

        /* setup any fd events */
        for (fde = select_ev->ev->fd_events; fde; fde = fde->next) {
                if (fde->flags & TEVENT_FD_READ) {
                        FD_SET(fde->fd, &r_fds);
                }
                if (fde->flags & TEVENT_FD_WRITE) {
                        FD_SET(fde->fd, &w_fds);
                }
        }

        if (select_ev->ev->signal_events &&
            tevent_common_check_signal(select_ev->ev)) {
                return 0;
        }

        selrtn = select(select_ev->maxfd+1, &r_fds, &w_fds, NULL, tvalp);

        if (selrtn == -1 && errno == EINTR && 
            select_ev->ev->signal_events) {
                tevent_common_check_signal(select_ev->ev);
                return 0;
        }

        if (selrtn == -1 && errno == EBADF) {
                /* the socket is dead! this should never
                   happen as the socket should have first been
                   made readable and that should have removed
                   the event, so this must be a bug. This is a
                   fatal error. */
                tevent_debug(select_ev->ev, TEVENT_DEBUG_FATAL,
                             "ERROR: EBADF on select_event_loop_once\n");
                select_ev->exit_code = EBADF;
                return -1;
        }

        if (selrtn == 0 && tvalp) {
                /* we don't care about a possible delay here */
                tevent_common_loop_timer_delay(select_ev->ev);
                return 0;
        }

        if (selrtn > 0) {
                /* at least one file descriptor is ready - check
                   which ones and call the handler, being careful to allow
                   the handler to remove itself when called */
                for (fde = select_ev->ev->fd_events; fde; fde = fde->next) {
                        uint16_t flags = 0;

                        if (FD_ISSET(fde->fd, &r_fds)) flags |= TEVENT_FD_READ;
                        if (FD_ISSET(fde->fd, &w_fds)) flags |= TEVENT_FD_WRITE;
                        if (flags) {
                                fde->handler(select_ev->ev, fde, flags, fde->private_data);
                                break;
                        }
                }
        }

        return 0;
}

/*
  do a single event loop using the events defined in ev 
*/
static int select_event_loop_once(struct tevent_context *ev, const char *location)
{
        struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
                                                           struct select_event_context);
        struct timeval tval;

        if (ev->signal_events &&
            tevent_common_check_signal(ev)) {
                return 0;
        }

        if (ev->immediate_events &&
            tevent_common_loop_immediate(ev)) {
                return 0;
        }

        tval = tevent_common_loop_timer_delay(ev);
        if (tevent_timeval_is_zero(&tval)) {
                return 0;
        }

        return select_event_loop_select(select_ev, &tval);
}

static const struct tevent_ops select_event_ops = {
        .context_init           = select_event_context_init,
        .add_fd                 = select_event_add_fd,
        .set_fd_close_fn        = tevent_common_fd_set_close_fn,
        .get_fd_flags           = tevent_common_fd_get_flags,
        .set_fd_flags           = tevent_common_fd_set_flags,
        .add_timer              = tevent_common_add_timer,
        .schedule_immediate     = tevent_common_schedule_immediate,
        .add_signal             = tevent_common_add_signal,
        .loop_once              = select_event_loop_once,
        .loop_wait              = tevent_common_loop_wait,
};

bool tevent_select_init(void)
{
        return tevent_register_backend("select", &select_event_ops);
}