tevent: don't skip a fd event if the previous one was deleted during poll()

[Samba.git] / lib / tevent / tevent_poll.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 poll_event_context {
        /* a pointer back to the generic event_context */
        struct tevent_context *ev;

        /*
         * A DLIST for fresh fde's added by poll_event_add_fd but not
         * picked up yet by poll_event_loop_once
         */
        struct tevent_fd *fresh;

        /*
         * These two arrays are maintained together.
         */
        struct pollfd *fds;
        struct tevent_fd **fdes;
        unsigned num_fds;

        /*
         * Signal fd to wake the poll() thread
         */
        int signal_fd;

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

static int poll_event_context_destructor(struct poll_event_context *poll_ev)
{
        struct tevent_fd *fd, *fn;

        for (fd = poll_ev->fresh; fd; fd = fn) {
                fn = fd->next;
                fd->event_ctx = NULL;
                DLIST_REMOVE(poll_ev->fresh, fd);
        }

        if (poll_ev->signal_fd == -1) {
                /*
                 * Non-threaded, no signal pipe
                 */
                return 0;
        }

        close(poll_ev->signal_fd);
        poll_ev->signal_fd = -1;

        if (poll_ev->num_fds == 0) {
                return 0;
        }
        if (poll_ev->fds[0].fd != -1) {
                close(poll_ev->fds[0].fd);
                poll_ev->fds[0].fd = -1;
        }
        return 0;
}

/*
  create a poll_event_context structure.
*/
static int poll_event_context_init(struct tevent_context *ev)
{
        struct poll_event_context *poll_ev;

        /*
         * we might be called during tevent_re_initialise()
         * which means we need to free our old additional_data
         * in order to detach old fd events from the
         * poll_ev->fresh list
         */
        TALLOC_FREE(ev->additional_data);

        poll_ev = talloc_zero(ev, struct poll_event_context);
        if (poll_ev == NULL) {
                return -1;
        }
        poll_ev->ev = ev;
        poll_ev->signal_fd = -1;
        ev->additional_data = poll_ev;
        talloc_set_destructor(poll_ev, poll_event_context_destructor);
        return 0;
}

static bool set_nonblock(int fd)
{
        int val;

        val = fcntl(fd, F_GETFL, 0);
        if (val == -1) {
                return false;
        }
        val |= O_NONBLOCK;

        return (fcntl(fd, F_SETFL, val) != -1);
}

static int poll_event_context_init_mt(struct tevent_context *ev)
{
        struct poll_event_context *poll_ev;
        struct pollfd *pfd;
        int fds[2];
        int ret;

        ret = poll_event_context_init(ev);
        if (ret == -1) {
                return ret;
        }

        poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        poll_ev->fds = talloc_zero(poll_ev, struct pollfd);
        if (poll_ev->fds == NULL) {
                return -1;
        }

        ret = pipe(fds);
        if (ret == -1) {
                return -1;
        }

        if (!set_nonblock(fds[0]) || !set_nonblock(fds[1])) {
                close(fds[0]);
                close(fds[1]);
                return -1;
        }

        poll_ev->signal_fd = fds[1];

        pfd = &poll_ev->fds[0];
        pfd->fd = fds[0];
        pfd->events = (POLLIN|POLLHUP);

        poll_ev->num_fds = 1;

        talloc_set_destructor(poll_ev, poll_event_context_destructor);

        return 0;
}

static void poll_event_wake_pollthread(struct poll_event_context *poll_ev)
{
        char c;
        ssize_t ret;

        if (poll_ev->signal_fd == -1) {
                return;
        }
        c = 0;
        do {
                ret = write(poll_ev->signal_fd, &c, sizeof(c));
        } while ((ret == -1) && (errno == EINTR));
}

static void poll_event_drain_signal_fd(struct poll_event_context *poll_ev)
{
        char buf[16];
        ssize_t ret;
        int fd;

        if (poll_ev->signal_fd == -1) {
                return;
        }

        if (poll_ev->num_fds < 1) {
                return;
        }
        fd = poll_ev->fds[0].fd;

        do {
                ret = read(fd, buf, sizeof(buf));
        } while (ret == sizeof(buf));
}

/*
  destroy an fd_event
*/
static int poll_event_fd_destructor(struct tevent_fd *fde)
{
        struct tevent_context *ev = fde->event_ctx;
        struct poll_event_context *poll_ev;
        uint64_t del_idx = fde->additional_flags;

        if (ev == NULL) {
                goto done;
        }

        poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        poll_ev->fdes[del_idx] = NULL;
        poll_event_wake_pollthread(poll_ev);
done:
        return tevent_common_fd_destructor(fde);
}

static int poll_fresh_fde_destructor(struct tevent_fd *fde)
{
        struct tevent_context *ev = fde->event_ctx;
        struct poll_event_context *poll_ev;

        if (ev == NULL) {
                goto done;
        }
        poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        DLIST_REMOVE(poll_ev->fresh, fde);
done:
        return tevent_common_fd_destructor(fde);
}

static void poll_event_schedule_immediate(struct tevent_immediate *im,
                                          struct tevent_context *ev,
                                          tevent_immediate_handler_t handler,
                                          void *private_data,
                                          const char *handler_name,
                                          const char *location)
{
        struct poll_event_context *poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        tevent_common_schedule_immediate(im, ev, handler, private_data,
                                         handler_name, location);
        poll_event_wake_pollthread(poll_ev);
}

/*
  Private function called by "standard" backend fallback.
  Note this only allows fallback to "poll" backend, not "poll-mt".
*/
_PRIVATE_ void tevent_poll_event_add_fd_internal(struct tevent_context *ev,
                                                 struct tevent_fd *fde)
{
        struct poll_event_context *poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        fde->additional_flags   = UINT64_MAX;
        fde->additional_data    = NULL;
        DLIST_ADD(poll_ev->fresh, fde);
        talloc_set_destructor(fde, poll_fresh_fde_destructor);
}

/*
  add a fd based event
  return NULL on failure (memory allocation error)
*/
static struct tevent_fd *poll_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 poll_event_context *poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);
        struct tevent_fd *fde;

        if (fd < 0) {
                return NULL;
        }

        fde = talloc(mem_ctx ? mem_ctx : ev, struct tevent_fd);
        if (fde == NULL) {
                return NULL;
        }
        fde->event_ctx          = ev;
        fde->fd                 = fd;
        fde->flags              = flags;
        fde->handler            = handler;
        fde->close_fn           = NULL;
        fde->private_data       = private_data;
        fde->handler_name       = handler_name;
        fde->location           = location;
        fde->additional_flags   = UINT64_MAX;
        fde->additional_data    = NULL;

        DLIST_ADD(poll_ev->fresh, fde);
        talloc_set_destructor(fde, poll_fresh_fde_destructor);
        poll_event_wake_pollthread(poll_ev);

        /*
         * poll_event_loop_poll will take care of the rest in
         * poll_event_setup_fresh
         */
        return fde;
}

/*
  set the fd event flags
*/
static void poll_event_set_fd_flags(struct tevent_fd *fde, uint16_t flags)
{
        struct tevent_context *ev = fde->event_ctx;
        struct poll_event_context *poll_ev;
        uint64_t idx = fde->additional_flags;
        uint16_t pollflags;

        if (ev == NULL) {
                return;
        }
        poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        fde->flags = flags;

        if (idx == UINT64_MAX) {
                /*
                 * poll_event_setup_fresh not yet called after this fde was
                 * added. We don't have to do anything to transfer the changed
                 * flags to the array passed to poll(2)
                 */
                return;
        }

        pollflags = 0;

        if (flags & TEVENT_FD_READ) {
                pollflags |= (POLLIN|POLLHUP);
        }
        if (flags & TEVENT_FD_WRITE) {
                pollflags |= (POLLOUT);
        }
        poll_ev->fds[idx].events = pollflags;

        poll_event_wake_pollthread(poll_ev);
}

static bool poll_event_setup_fresh(struct tevent_context *ev,
                                   struct poll_event_context *poll_ev)
{
        struct tevent_fd *fde, *next;
        unsigned num_fresh, num_fds;

        if (poll_ev->fresh == NULL) {
                return true;
        }

        num_fresh = 0;
        for (fde = poll_ev->fresh; fde; fde = fde->next) {
                num_fresh += 1;
        }
        num_fds = poll_ev->num_fds + num_fresh;

        /*
         * We check the length of fdes here. It is the last one
         * enlarged, so if the realloc for poll_fd->fdes fails,
         * poll_fd->fds will have at least the size of poll_fd->fdes
         */

        if (num_fds >= talloc_array_length(poll_ev->fdes)) {
                struct pollfd *tmp_fds;
                struct tevent_fd **tmp_fdes;
                unsigned array_length;

                array_length = (num_fds + 15) & ~15; /* round up to 16 */

                tmp_fds = talloc_realloc(
                        poll_ev, poll_ev->fds, struct pollfd, array_length);
                if (tmp_fds == NULL) {
                        return false;
                }
                poll_ev->fds = tmp_fds;

                tmp_fdes = talloc_realloc(
                        poll_ev, poll_ev->fdes, struct tevent_fd *,
                        array_length);
                if (tmp_fdes == NULL) {
                        return false;
                }
                poll_ev->fdes = tmp_fdes;
        }

        for (fde = poll_ev->fresh; fde; fde = next) {
                struct pollfd *pfd;

                pfd = &poll_ev->fds[poll_ev->num_fds];

                pfd->fd = fde->fd;
                pfd->events = 0;
                pfd->revents = 0;

                if (fde->flags & TEVENT_FD_READ) {
                        pfd->events |= (POLLIN|POLLHUP);
                }
                if (fde->flags & TEVENT_FD_WRITE) {
                        pfd->events |= (POLLOUT);
                }

                fde->additional_flags = poll_ev->num_fds;
                poll_ev->fdes[poll_ev->num_fds] = fde;

                next = fde->next;
                DLIST_REMOVE(poll_ev->fresh, fde);
                DLIST_ADD(ev->fd_events, fde);

                talloc_set_destructor(fde, poll_event_fd_destructor);

                poll_ev->num_fds += 1;
        }
        return true;
}

/*
  event loop handling using poll()
*/
static int poll_event_loop_poll(struct tevent_context *ev,
                                struct timeval *tvalp)
{
        struct poll_event_context *poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);
        int pollrtn;
        int timeout = -1;
        unsigned first_fd;
        unsigned i, next_i;
        int poll_errno;

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

        if (tvalp != NULL) {
                timeout = tvalp->tv_sec * 1000;
                timeout += (tvalp->tv_usec + 999) / 1000;
        }

        poll_event_drain_signal_fd(poll_ev);

        if (!poll_event_setup_fresh(ev, poll_ev)) {
                return -1;
        }

        tevent_trace_point_callback(poll_ev->ev, TEVENT_TRACE_BEFORE_WAIT);
        pollrtn = poll(poll_ev->fds, poll_ev->num_fds, timeout);
        poll_errno = errno;
        tevent_trace_point_callback(poll_ev->ev, TEVENT_TRACE_AFTER_WAIT);

        if (pollrtn == -1 && poll_errno == EINTR && ev->signal_events) {
                tevent_common_check_signal(ev);
                return 0;
        }

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

        if (pollrtn <= 0) {
                /*
                 * No fd's ready
                 */
                return 0;
        }

        first_fd = (poll_ev->signal_fd != -1) ? 1 : 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 (i=first_fd; i<poll_ev->num_fds; i = next_i) {
                struct pollfd *pfd;
                struct tevent_fd *fde;
                uint16_t flags = 0;

                next_i = i + 1;

                fde = poll_ev->fdes[i];
                if (fde == NULL) {
                        /*
                         * This fde was talloc_free()'ed. Delete it
                         * from the arrays
                         */
                        poll_ev->num_fds -= 1;
                        if (poll_ev->num_fds == i) {
                                break;
                        }
                        poll_ev->fds[i] = poll_ev->fds[poll_ev->num_fds];
                        poll_ev->fdes[i] = poll_ev->fdes[poll_ev->num_fds];
                        if (poll_ev->fdes[i] != NULL) {
                                poll_ev->fdes[i]->additional_flags = i;
                        }
                        /* we have to reprocess position 'i' */
                        next_i = i;
                        continue;
                }

                pfd = &poll_ev->fds[i];

                if (pfd->revents & (POLLHUP|POLLERR)) {
                        /* If we only wait for TEVENT_FD_WRITE, we
                           should not tell the event handler about it,
                           and remove the writable flag, as we only
                           report errors when waiting for read events
                           to match the select behavior. */
                        if (!(fde->flags & TEVENT_FD_READ)) {
                                TEVENT_FD_NOT_WRITEABLE(fde);
                                continue;
                        }
                        flags |= TEVENT_FD_READ;
                }
                if (pfd->revents & POLLIN) {
                        flags |= TEVENT_FD_READ;
                }
                if (pfd->revents & POLLOUT) {
                        flags |= TEVENT_FD_WRITE;
                }
                if (flags != 0) {
                        fde->handler(ev, fde, flags, fde->private_data);
                        break;
                }
        }

        return 0;
}

/*
  do a single event loop using the events defined in ev
*/
static int poll_event_loop_once(struct tevent_context *ev,
                                const char *location)
{
        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 poll_event_loop_poll(ev, &tval);
}

static int poll_event_loop_wait(struct tevent_context *ev,
                                const char *location)
{
        struct poll_event_context *poll_ev = talloc_get_type_abort(
                ev->additional_data, struct poll_event_context);

        /*
         * loop as long as we have events pending
         */
        while (ev->fd_events ||
               ev->timer_events ||
               ev->immediate_events ||
               ev->signal_events ||
               poll_ev->fresh) {
                int ret;
                ret = _tevent_loop_once(ev, location);
                if (ret != 0) {
                        tevent_debug(ev, TEVENT_DEBUG_FATAL,
                                     "_tevent_loop_once() failed: %d - %s\n",
                                     ret, strerror(errno));
                        return ret;
                }
        }

        tevent_debug(ev, TEVENT_DEBUG_WARNING,
                     "poll_event_loop_wait() out of events\n");
        return 0;
}

static const struct tevent_ops poll_event_ops = {
        .context_init           = poll_event_context_init,
        .add_fd                 = poll_event_add_fd,
        .set_fd_close_fn        = tevent_common_fd_set_close_fn,
        .get_fd_flags           = tevent_common_fd_get_flags,
        .set_fd_flags           = poll_event_set_fd_flags,
        .add_timer              = tevent_common_add_timer,
        .schedule_immediate     = tevent_common_schedule_immediate,
        .add_signal             = tevent_common_add_signal,
        .loop_once              = poll_event_loop_once,
        .loop_wait              = poll_event_loop_wait,
};

_PRIVATE_ bool tevent_poll_init(void)
{
        return tevent_register_backend("poll", &poll_event_ops);
}

static const struct tevent_ops poll_event_mt_ops = {
        .context_init           = poll_event_context_init_mt,
        .add_fd                 = poll_event_add_fd,
        .set_fd_close_fn        = tevent_common_fd_set_close_fn,
        .get_fd_flags           = tevent_common_fd_get_flags,
        .set_fd_flags           = poll_event_set_fd_flags,
        .add_timer              = tevent_common_add_timer,
        .schedule_immediate     = poll_event_schedule_immediate,
        .add_signal             = tevent_common_add_signal,
        .loop_once              = poll_event_loop_once,
        .loop_wait              = poll_event_loop_wait,
};

_PRIVATE_ bool tevent_poll_mt_init(void)
{
        return tevent_register_backend("poll_mt", &poll_event_mt_ops);
}