/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2013 Lennart Poettering

  systemd 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 2.1 of the License, or
  (at your option) any later version.

  systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <sys/epoll.h>
#include <sys/timerfd.h>
#include <sys/wait.h>
#include <pthread.h>

#include "sd-id128.h"
#include "sd-daemon.h"
#include "macro.h"
#include "prioq.h"
#include "hashmap.h"
#include "util.h"
#include "time-util.h"
#include "missing.h"

#include "sd-event.h"

#define EPOLL_QUEUE_MAX 512U
#define DEFAULT_ACCURACY_USEC (250 * USEC_PER_MSEC)

typedef enum EventSourceType {
        SOURCE_IO,
        SOURCE_MONOTONIC,
        SOURCE_REALTIME,
        SOURCE_SIGNAL,
        SOURCE_CHILD,
        SOURCE_DEFER,
        SOURCE_EXIT,
        SOURCE_WATCHDOG
} EventSourceType;

struct sd_event_source {
        unsigned n_ref;

        sd_event *event;
        void *userdata;
        sd_event_handler_t prepare;

        EventSourceType type:4;
        int enabled:3;
        bool pending:1;
        bool dispatching:1;

        int64_t priority;
        unsigned pending_index;
        unsigned prepare_index;
        unsigned pending_iteration;
        unsigned prepare_iteration;

        union {
                struct {
                        sd_event_io_handler_t callback;
                        int fd;
                        uint32_t events;
                        uint32_t revents;
                        bool registered:1;
                } io;
                struct {
                        sd_event_time_handler_t callback;
                        usec_t next, accuracy;
                        unsigned earliest_index;
                        unsigned latest_index;
                } time;
                struct {
                        sd_event_signal_handler_t callback;
                        struct signalfd_siginfo siginfo;
                        int sig;
                } signal;
                struct {
                        sd_event_child_handler_t callback;
                        siginfo_t siginfo;
                        pid_t pid;
                        int options;
                } child;
                struct {
                        sd_event_handler_t callback;
                } defer;
                struct {
                        sd_event_handler_t callback;
                        unsigned prioq_index;
                } exit;
        };
};

struct sd_event {
        unsigned n_ref;

        int epoll_fd;
        int signal_fd;
        int realtime_fd;
        int monotonic_fd;
        int watchdog_fd;

        Prioq *pending;
        Prioq *prepare;

        /* For both clocks we maintain two priority queues each, one
         * ordered for the earliest times the events may be
         * dispatched, and one ordered by the latest times they must
         * have been dispatched. The range between the top entries in
         * the two prioqs is the time window we can freely schedule
         * wakeups in */
        Prioq *monotonic_earliest;
        Prioq *monotonic_latest;
        Prioq *realtime_earliest;
        Prioq *realtime_latest;

        usec_t realtime_next, monotonic_next;
        usec_t perturb;

        sigset_t sigset;
        sd_event_source **signal_sources;

        Hashmap *child_sources;
        unsigned n_enabled_child_sources;

        Prioq *exit;

        pid_t original_pid;

        unsigned iteration;
        dual_timestamp timestamp;
        int state;

        bool exit_requested:1;
        bool need_process_child:1;
        bool watchdog:1;

        int exit_code;

        pid_t tid;
        sd_event **default_event_ptr;

        usec_t watchdog_last, watchdog_period;

        unsigned n_sources;
};

static int pending_prioq_compare(const void *a, const void *b) {
        const sd_event_source *x = a, *y = b;

        assert(x->pending);
        assert(y->pending);

        /* Enabled ones first */
        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
                return -1;
        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
                return 1;

        /* Lower priority values first */
        if (x->priority < y->priority)
                return -1;
        if (x->priority > y->priority)
                return 1;

        /* Older entries first */
        if (x->pending_iteration < y->pending_iteration)
                return -1;
        if (x->pending_iteration > y->pending_iteration)
                return 1;

        /* Stability for the rest */
        if (x < y)
                return -1;
        if (x > y)
                return 1;

        return 0;
}

static int prepare_prioq_compare(const void *a, const void *b) {
        const sd_event_source *x = a, *y = b;

        assert(x->prepare);
        assert(y->prepare);

        /* Move most recently prepared ones last, so that we can stop
         * preparing as soon as we hit one that has already been
         * prepared in the current iteration */
        if (x->prepare_iteration < y->prepare_iteration)
                return -1;
        if (x->prepare_iteration > y->prepare_iteration)
                return 1;

        /* Enabled ones first */
        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
                return -1;
        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
                return 1;

        /* Lower priority values first */
        if (x->priority < y->priority)
                return -1;
        if (x->priority > y->priority)
                return 1;

        /* Stability for the rest */
        if (x < y)
                return -1;
        if (x > y)
                return 1;

        return 0;
}

static int earliest_time_prioq_compare(const void *a, const void *b) {
        const sd_event_source *x = a, *y = b;

        assert(x->type == SOURCE_MONOTONIC || x->type == SOURCE_REALTIME);
        assert(y->type == SOURCE_MONOTONIC || y->type == SOURCE_REALTIME);

        /* Enabled ones first */
        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
                return -1;
        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
                return 1;

        /* Move the pending ones to the end */
        if (!x->pending && y->pending)
                return -1;
        if (x->pending && !y->pending)
                return 1;

        /* Order by time */
        if (x->time.next < y->time.next)
                return -1;
        if (x->time.next > y->time.next)
                return 1;

        /* Stability for the rest */
        if (x < y)
                return -1;
        if (x > y)
                return 1;

        return 0;
}

static int latest_time_prioq_compare(const void *a, const void *b) {
        const sd_event_source *x = a, *y = b;

        assert((x->type == SOURCE_MONOTONIC && y->type == SOURCE_MONOTONIC) ||
               (x->type == SOURCE_REALTIME && y->type == SOURCE_REALTIME));

        /* Enabled ones first */
        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
                return -1;
        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
                return 1;

        /* Move the pending ones to the end */
        if (!x->pending && y->pending)
                return -1;
        if (x->pending && !y->pending)
                return 1;

        /* Order by time */
        if (x->time.next + x->time.accuracy < y->time.next + y->time.accuracy)
                return -1;
        if (x->time.next + x->time.accuracy > y->time.next + y->time.accuracy)
                return 1;

        /* Stability for the rest */
        if (x < y)
                return -1;
        if (x > y)
                return 1;

        return 0;
}

static int exit_prioq_compare(const void *a, const void *b) {
        const sd_event_source *x = a, *y = b;

        assert(x->type == SOURCE_EXIT);
        assert(y->type == SOURCE_EXIT);

        /* Enabled ones first */
        if (x->enabled != SD_EVENT_OFF && y->enabled == SD_EVENT_OFF)
                return -1;
        if (x->enabled == SD_EVENT_OFF && y->enabled != SD_EVENT_OFF)
                return 1;

        /* Lower priority values first */
        if (x->priority < y->priority)
                return -1;
        if (x->priority > y->priority)
                return 1;

        /* Stability for the rest */
        if (x < y)
                return -1;
        if (x > y)
                return 1;

        return 0;
}

static void event_free(sd_event *e) {
        assert(e);
        assert(e->n_sources == 0);

        if (e->default_event_ptr)
                *(e->default_event_ptr) = NULL;

        if (e->epoll_fd >= 0)
                close_nointr_nofail(e->epoll_fd);

        if (e->signal_fd >= 0)
                close_nointr_nofail(e->signal_fd);

        if (e->realtime_fd >= 0)
                close_nointr_nofail(e->realtime_fd);

        if (e->monotonic_fd >= 0)
                close_nointr_nofail(e->monotonic_fd);

        if (e->watchdog_fd >= 0)
                close_nointr_nofail(e->watchdog_fd);

        prioq_free(e->pending);
        prioq_free(e->prepare);
        prioq_free(e->monotonic_earliest);
        prioq_free(e->monotonic_latest);
        prioq_free(e->realtime_earliest);
        prioq_free(e->realtime_latest);
        prioq_free(e->exit);

        free(e->signal_sources);

        hashmap_free(e->child_sources);
        free(e);
}

_public_ int sd_event_new(sd_event** ret) {
        sd_event *e;
        int r;

        assert_return(ret, -EINVAL);

        e = new0(sd_event, 1);
        if (!e)
                return -ENOMEM;

        e->n_ref = 1;
        e->signal_fd = e->realtime_fd = e->monotonic_fd = e->watchdog_fd = e->epoll_fd = -1;
        e->realtime_next = e->monotonic_next = (usec_t) -1;
        e->original_pid = getpid();

        assert_se(sigemptyset(&e->sigset) == 0);

        e->pending = prioq_new(pending_prioq_compare);
        if (!e->pending) {
                r = -ENOMEM;
                goto fail;
        }

        e->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
        if (e->epoll_fd < 0) {
                r = -errno;
                goto fail;
        }

        *ret = e;
        return 0;

fail:
        event_free(e);
        return r;
}

_public_ sd_event* sd_event_ref(sd_event *e) {
        assert_return(e, NULL);

        assert(e->n_ref >= 1);
        e->n_ref++;

        return e;
}

_public_ sd_event* sd_event_unref(sd_event *e) {

        if (!e)
                return NULL;

        assert(e->n_ref >= 1);
        e->n_ref--;

        if (e->n_ref <= 0)
                event_free(e);

        return NULL;
}

static bool event_pid_changed(sd_event *e) {
        assert(e);

        /* We don't support people creating am event loop and keeping
         * it around over a fork(). Let's complain. */

        return e->original_pid != getpid();
}

static int source_io_unregister(sd_event_source *s) {
        int r;

        assert(s);
        assert(s->type == SOURCE_IO);

        if (!s->io.registered)
                return 0;

        r = epoll_ctl(s->event->epoll_fd, EPOLL_CTL_DEL, s->io.fd, NULL);
        if (r < 0)
                return -errno;

        s->io.registered = false;
        return 0;
}

static int source_io_register(
                sd_event_source *s,
                int enabled,
                uint32_t events) {

        struct epoll_event ev = {};
        int r;

        assert(s);
        assert(s->type == SOURCE_IO);
        assert(enabled != SD_EVENT_OFF);

        ev.events = events;
        ev.data.ptr = s;

        if (enabled == SD_EVENT_ONESHOT)
                ev.events |= EPOLLONESHOT;

        if (s->io.registered)
                r = epoll_ctl(s->event->epoll_fd, EPOLL_CTL_MOD, s->io.fd, &ev);
        else
                r = epoll_ctl(s->event->epoll_fd, EPOLL_CTL_ADD, s->io.fd, &ev);

        if (r < 0)
                return -errno;

        s->io.registered = true;

        return 0;
}

static void source_free(sd_event_source *s) {
        assert(s);

        if (s->event) {
                assert(s->event->n_sources > 0);

                switch (s->type) {

                case SOURCE_IO:
                        if (s->io.fd >= 0)
                                source_io_unregister(s);

                        break;

                case SOURCE_MONOTONIC:
                        prioq_remove(s->event->monotonic_earliest, s, &s->time.earliest_index);
                        prioq_remove(s->event->monotonic_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_REALTIME:
                        prioq_remove(s->event->realtime_earliest, s, &s->time.earliest_index);
                        prioq_remove(s->event->realtime_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_SIGNAL:
                        if (s->signal.sig > 0) {
                                if (s->signal.sig != SIGCHLD || s->event->n_enabled_child_sources == 0)
                                        assert_se(sigdelset(&s->event->sigset, s->signal.sig) == 0);

                                if (s->event->signal_sources)
                                        s->event->signal_sources[s->signal.sig] = NULL;
                        }

                        break;

                case SOURCE_CHILD:
                        if (s->child.pid > 0) {
                                if (s->enabled != SD_EVENT_OFF) {
                                        assert(s->event->n_enabled_child_sources > 0);
                                        s->event->n_enabled_child_sources--;
                                }

                                if (!s->event->signal_sources || !s->event->signal_sources[SIGCHLD])
                                        assert_se(sigdelset(&s->event->sigset, SIGCHLD) == 0);

                                hashmap_remove(s->event->child_sources, INT_TO_PTR(s->child.pid));
                        }

                        break;

                case SOURCE_DEFER:
                        /* nothing */
                        break;

                case SOURCE_EXIT:
                        prioq_remove(s->event->exit, s, &s->exit.prioq_index);
                        break;

                case SOURCE_WATCHDOG:
                        assert_not_reached("Wut? I shouldn't exist.");
                }

                if (s->pending)
                        prioq_remove(s->event->pending, s, &s->pending_index);

                if (s->prepare)
                        prioq_remove(s->event->prepare, s, &s->prepare_index);

                s->event->n_sources--;
                sd_event_unref(s->event);
        }

        free(s);
}

static int source_set_pending(sd_event_source *s, bool b) {
        int r;

        assert(s);
        assert(s->type != SOURCE_EXIT);

        if (s->pending == b)
                return 0;

        s->pending = b;

        if (b) {
                s->pending_iteration = s->event->iteration;

                r = prioq_put(s->event->pending, s, &s->pending_index);
                if (r < 0) {
                        s->pending = false;
                        return r;
                }
        } else
                assert_se(prioq_remove(s->event->pending, s, &s->pending_index));

        if (s->type == SOURCE_REALTIME) {
                prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
                prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
        } else if (s->type == SOURCE_MONOTONIC) {
                prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
                prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
        }

        return 0;
}

static sd_event_source *source_new(sd_event *e, EventSourceType type) {
        sd_event_source *s;

        assert(e);

        s = new0(sd_event_source, 1);
        if (!s)
                return NULL;

        s->n_ref = 1;
        s->event = sd_event_ref(e);
        s->type = type;
        s->pending_index = s->prepare_index = PRIOQ_IDX_NULL;

        e->n_sources ++;

        return s;
}

_public_ int sd_event_add_io(
                sd_event *e,
                sd_event_source **ret,
                int fd,
                uint32_t events,
                sd_event_io_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        int r;

        assert_return(e, -EINVAL);
        assert_return(fd >= 0, -EINVAL);
        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET)), -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        s = source_new(e, SOURCE_IO);
        if (!s)
                return -ENOMEM;

        s->io.fd = fd;
        s->io.events = events;
        s->io.callback = callback;
        s->userdata = userdata;
        s->enabled = SD_EVENT_ON;

        r = source_io_register(s, s->enabled, events);
        if (r < 0) {
                source_free(s);
                return -errno;
        }

        *ret = s;
        return 0;
}

static int event_setup_timer_fd(
                sd_event *e,
                EventSourceType type,
                int *timer_fd,
                clockid_t id) {

        sd_id128_t bootid = {};
        struct epoll_event ev = {};
        int r, fd;

        assert(e);
        assert(timer_fd);

        if (_likely_(*timer_fd >= 0))
                return 0;

        fd = timerfd_create(id, TFD_NONBLOCK|TFD_CLOEXEC);
        if (fd < 0)
                return -errno;

        ev.events = EPOLLIN;
        ev.data.ptr = INT_TO_PTR(type);

        r = epoll_ctl(e->epoll_fd, EPOLL_CTL_ADD, fd, &ev);
        if (r < 0) {
                close_nointr_nofail(fd);
                return -errno;
        }

        /* When we sleep for longer, we try to realign the wakeup to
           the same time wihtin each minute/second/250ms, so that
           events all across the system can be coalesced into a single
           CPU wakeup. However, let's take some system-specific
           randomness for this value, so that in a network of systems
           with synced clocks timer events are distributed a
           bit. Here, we calculate a perturbation usec offset from the
           boot ID. */

        if (sd_id128_get_boot(&bootid) >= 0)
                e->perturb = (bootid.qwords[0] ^ bootid.qwords[1]) % USEC_PER_MINUTE;

        *timer_fd = fd;
        return 0;
}

static int event_add_time_internal(
                sd_event *e,
                sd_event_source **ret,
                EventSourceType type,
                int *timer_fd,
                clockid_t id,
                Prioq **earliest,
                Prioq **latest,
                uint64_t usec,
                uint64_t accuracy,
                sd_event_time_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        int r;

        assert_return(e, -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(usec != (uint64_t) -1, -EINVAL);
        assert_return(accuracy != (uint64_t) -1, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        assert(timer_fd);
        assert(earliest);
        assert(latest);

        if (!*earliest) {
                *earliest = prioq_new(earliest_time_prioq_compare);
                if (!*earliest)
                        return -ENOMEM;
        }

        if (!*latest) {
                *latest = prioq_new(latest_time_prioq_compare);
                if (!*latest)
                        return -ENOMEM;
        }

        if (*timer_fd < 0) {
                r = event_setup_timer_fd(e, type, timer_fd, id);
                if (r < 0)
                        return r;
        }

        s = source_new(e, type);
        if (!s)
                return -ENOMEM;

        s->time.next = usec;
        s->time.accuracy = accuracy == 0 ? DEFAULT_ACCURACY_USEC : accuracy;
        s->time.callback = callback;
        s->time.earliest_index = s->time.latest_index = PRIOQ_IDX_NULL;
        s->userdata = userdata;
        s->enabled = SD_EVENT_ONESHOT;

        r = prioq_put(*earliest, s, &s->time.earliest_index);
        if (r < 0)
                goto fail;

        r = prioq_put(*latest, s, &s->time.latest_index);
        if (r < 0)
                goto fail;

        *ret = s;
        return 0;

fail:
        source_free(s);
        return r;
}

_public_ int sd_event_add_monotonic(sd_event *e,
                                    sd_event_source **ret,
                                    uint64_t usec,
                                    uint64_t accuracy,
                                    sd_event_time_handler_t callback,
                                    void *userdata) {

        return event_add_time_internal(e, ret, SOURCE_MONOTONIC, &e->monotonic_fd, CLOCK_MONOTONIC, &e->monotonic_earliest, &e->monotonic_latest, usec, accuracy, callback, userdata);
}

_public_ int sd_event_add_realtime(sd_event *e,
                                   sd_event_source **ret,
                                   uint64_t usec,
                                   uint64_t accuracy,
                                   sd_event_time_handler_t callback,
                                   void *userdata) {

        return event_add_time_internal(e, ret, SOURCE_REALTIME, &e->realtime_fd, CLOCK_REALTIME, &e->realtime_earliest, &e->monotonic_latest, usec, accuracy, callback, userdata);
}

static int event_update_signal_fd(sd_event *e) {
        struct epoll_event ev = {};
        bool add_to_epoll;
        int r;

        assert(e);

        add_to_epoll = e->signal_fd < 0;

        r = signalfd(e->signal_fd, &e->sigset, SFD_NONBLOCK|SFD_CLOEXEC);
        if (r < 0)
                return -errno;

        e->signal_fd = r;

        if (!add_to_epoll)
                return 0;

        ev.events = EPOLLIN;
        ev.data.ptr = INT_TO_PTR(SOURCE_SIGNAL);

        r = epoll_ctl(e->epoll_fd, EPOLL_CTL_ADD, e->signal_fd, &ev);
        if (r < 0) {
                close_nointr_nofail(e->signal_fd);
                e->signal_fd = -1;

                return -errno;
        }

        return 0;
}

_public_ int sd_event_add_signal(
                sd_event *e,
                sd_event_source **ret,
                int sig,
                sd_event_signal_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        sigset_t ss;
        int r;

        assert_return(e, -EINVAL);
        assert_return(sig > 0, -EINVAL);
        assert_return(sig < _NSIG, -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        r = pthread_sigmask(SIG_SETMASK, NULL, &ss);
        if (r < 0)
                return -errno;

        if (!sigismember(&ss, sig))
                return -EBUSY;

        if (!e->signal_sources) {
                e->signal_sources = new0(sd_event_source*, _NSIG);
                if (!e->signal_sources)
                        return -ENOMEM;
        } else if (e->signal_sources[sig])
                return -EBUSY;

        s = source_new(e, SOURCE_SIGNAL);
        if (!s)
                return -ENOMEM;

        s->signal.sig = sig;
        s->signal.callback = callback;
        s->userdata = userdata;
        s->enabled = SD_EVENT_ON;

        e->signal_sources[sig] = s;
        assert_se(sigaddset(&e->sigset, sig) == 0);

        if (sig != SIGCHLD || e->n_enabled_child_sources == 0) {
                r = event_update_signal_fd(e);
                if (r < 0) {
                        source_free(s);
                        return r;
                }
        }

        *ret = s;
        return 0;
}

_public_ int sd_event_add_child(
                sd_event *e,
                sd_event_source **ret,
                pid_t pid,
                int options,
                sd_event_child_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        int r;

        assert_return(e, -EINVAL);
        assert_return(pid > 1, -EINVAL);
        assert_return(!(options & ~(WEXITED|WSTOPPED|WCONTINUED)), -EINVAL);
        assert_return(options != 0, -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        r = hashmap_ensure_allocated(&e->child_sources, trivial_hash_func, trivial_compare_func);
        if (r < 0)
                return r;

        if (hashmap_contains(e->child_sources, INT_TO_PTR(pid)))
                return -EBUSY;

        s = source_new(e, SOURCE_CHILD);
        if (!s)
                return -ENOMEM;

        s->child.pid = pid;
        s->child.options = options;
        s->child.callback = callback;
        s->userdata = userdata;
        s->enabled = SD_EVENT_ONESHOT;

        r = hashmap_put(e->child_sources, INT_TO_PTR(pid), s);
        if (r < 0) {
                source_free(s);
                return r;
        }

        e->n_enabled_child_sources ++;

        assert_se(sigaddset(&e->sigset, SIGCHLD) == 0);

        if (!e->signal_sources || !e->signal_sources[SIGCHLD]) {
                r = event_update_signal_fd(e);
                if (r < 0) {
                        source_free(s);
                        return -errno;
                }
        }

        e->need_process_child = true;

        *ret = s;
        return 0;
}

_public_ int sd_event_add_defer(
                sd_event *e,
                sd_event_source **ret,
                sd_event_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        int r;

        assert_return(e, -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        s = source_new(e, SOURCE_DEFER);
        if (!s)
                return -ENOMEM;

        s->defer.callback = callback;
        s->userdata = userdata;
        s->enabled = SD_EVENT_ONESHOT;

        r = source_set_pending(s, true);
        if (r < 0) {
                source_free(s);
                return r;
        }

        *ret = s;
        return 0;
}

_public_ int sd_event_add_exit(
                sd_event *e,
                sd_event_source **ret,
                sd_event_handler_t callback,
                void *userdata) {

        sd_event_source *s;
        int r;

        assert_return(e, -EINVAL);
        assert_return(callback, -EINVAL);
        assert_return(ret, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        if (!e->exit) {
                e->exit = prioq_new(exit_prioq_compare);
                if (!e->exit)
                        return -ENOMEM;
        }

        s = source_new(e, SOURCE_EXIT);
        if (!s)
                return -ENOMEM;

        s->exit.callback = callback;
        s->userdata = userdata;
        s->exit.prioq_index = PRIOQ_IDX_NULL;
        s->enabled = SD_EVENT_ONESHOT;

        r = prioq_put(s->event->exit, s, &s->exit.prioq_index);
        if (r < 0) {
                source_free(s);
                return r;
        }

        *ret = s;
        return 0;
}

_public_ sd_event_source* sd_event_source_ref(sd_event_source *s) {
        assert_return(s, NULL);

        assert(s->n_ref >= 1);
        s->n_ref++;

        return s;
}

_public_ sd_event_source* sd_event_source_unref(sd_event_source *s) {

        if (!s)
                return NULL;

        assert(s->n_ref >= 1);
        s->n_ref--;

        if (s->n_ref <= 0) {
                /* Here's a special hack: when we are called from a
                 * dispatch handler we won't free the event source
                 * immediately, but we will detach the fd from the
                 * epoll. This way it is safe for the caller to unref
                 * the event source and immediately close the fd, but
                 * we still retain a valid event source object after
                 * the callback. */

                if (s->dispatching) {
                        if (s->type == SOURCE_IO)
                                source_io_unregister(s);
                } else
                        source_free(s);
        }

        return NULL;
}

_public_ sd_event *sd_event_source_get_event(sd_event_source *s) {
        assert_return(s, NULL);

        return s->event;
}

_public_ int sd_event_source_get_pending(sd_event_source *s) {
        assert_return(s, -EINVAL);
        assert_return(s->type != SOURCE_EXIT, -EDOM);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        return s->pending;
}

_public_ int sd_event_source_get_io_fd(sd_event_source *s) {
        assert_return(s, -EINVAL);
        assert_return(s->type == SOURCE_IO, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        return s->io.fd;
}

_public_ int sd_event_source_set_io_fd(sd_event_source *s, int fd) {
        int r;

        assert_return(s, -EINVAL);
        assert_return(fd >= 0, -EINVAL);
        assert_return(s->type == SOURCE_IO, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (s->io.fd == fd)
                return 0;

        if (s->enabled == SD_EVENT_OFF) {
                s->io.fd = fd;
                s->io.registered = false;
        } else {
                int saved_fd;

                saved_fd = s->io.fd;
                assert(s->io.registered);

                s->io.fd = fd;
                s->io.registered = false;

                r = source_io_register(s, s->enabled, s->io.events);
                if (r < 0) {
                        s->io.fd = saved_fd;
                        s->io.registered = true;
                        return r;
                }

                epoll_ctl(s->event->epoll_fd, EPOLL_CTL_DEL, saved_fd, NULL);
        }

        return 0;
}

_public_ int sd_event_source_get_io_events(sd_event_source *s, uint32_t* events) {
        assert_return(s, -EINVAL);
        assert_return(events, -EINVAL);
        assert_return(s->type == SOURCE_IO, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *events = s->io.events;
        return 0;
}

_public_ int sd_event_source_set_io_events(sd_event_source *s, uint32_t events) {
        int r;

        assert_return(s, -EINVAL);
        assert_return(s->type == SOURCE_IO, -EDOM);
        assert_return(!(events & ~(EPOLLIN|EPOLLOUT|EPOLLRDHUP|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET)), -EINVAL);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (s->io.events == events)
                return 0;

        if (s->enabled != SD_EVENT_OFF) {
                r = source_io_register(s, s->enabled, events);
                if (r < 0)
                        return r;
        }

        s->io.events = events;
        source_set_pending(s, false);

        return 0;
}

_public_ int sd_event_source_get_io_revents(sd_event_source *s, uint32_t* revents) {
        assert_return(s, -EINVAL);
        assert_return(revents, -EINVAL);
        assert_return(s->type == SOURCE_IO, -EDOM);
        assert_return(s->pending, -ENODATA);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *revents = s->io.revents;
        return 0;
}

_public_ int sd_event_source_get_signal(sd_event_source *s) {
        assert_return(s, -EINVAL);
        assert_return(s->type == SOURCE_SIGNAL, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        return s->signal.sig;
}

_public_ int sd_event_source_get_priority(sd_event_source *s, int64_t *priority) {
        assert_return(s, -EINVAL);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        return s->priority;
}

_public_ int sd_event_source_set_priority(sd_event_source *s, int64_t priority) {
        assert_return(s, -EINVAL);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (s->priority == priority)
                return 0;

        s->priority = priority;

        if (s->pending)
                prioq_reshuffle(s->event->pending, s, &s->pending_index);

        if (s->prepare)
                prioq_reshuffle(s->event->prepare, s, &s->prepare_index);

        if (s->type == SOURCE_EXIT)
                prioq_reshuffle(s->event->exit, s, &s->exit.prioq_index);

        return 0;
}

_public_ int sd_event_source_get_enabled(sd_event_source *s, int *m) {
        assert_return(s, -EINVAL);
        assert_return(m, -EINVAL);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *m = s->enabled;
        return 0;
}

_public_ int sd_event_source_set_enabled(sd_event_source *s, int m) {
        int r;

        assert_return(s, -EINVAL);
        assert_return(m == SD_EVENT_OFF || m == SD_EVENT_ON || m == SD_EVENT_ONESHOT, -EINVAL);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (s->enabled == m)
                return 0;

        if (m == SD_EVENT_OFF) {

                switch (s->type) {

                case SOURCE_IO:
                        r = source_io_unregister(s);
                        if (r < 0)
                                return r;

                        s->enabled = m;
                        break;

                case SOURCE_MONOTONIC:
                        s->enabled = m;
                        prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
                        prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_REALTIME:
                        s->enabled = m;
                        prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
                        prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_SIGNAL:
                        s->enabled = m;
                        if (s->signal.sig != SIGCHLD || s->event->n_enabled_child_sources == 0) {
                                assert_se(sigdelset(&s->event->sigset, s->signal.sig) == 0);
                                event_update_signal_fd(s->event);
                        }

                        break;

                case SOURCE_CHILD:
                        s->enabled = m;

                        assert(s->event->n_enabled_child_sources > 0);
                        s->event->n_enabled_child_sources--;

                        if (!s->event->signal_sources || !s->event->signal_sources[SIGCHLD]) {
                                assert_se(sigdelset(&s->event->sigset, SIGCHLD) == 0);
                                event_update_signal_fd(s->event);
                        }

                        break;

                case SOURCE_EXIT:
                        s->enabled = m;
                        prioq_reshuffle(s->event->exit, s, &s->exit.prioq_index);
                        break;

                case SOURCE_DEFER:
                        s->enabled = m;
                        break;

                case SOURCE_WATCHDOG:
                        assert_not_reached("Wut? I shouldn't exist.");
                }

        } else {
                switch (s->type) {

                case SOURCE_IO:
                        r = source_io_register(s, m, s->io.events);
                        if (r < 0)
                                return r;

                        s->enabled = m;
                        break;

                case SOURCE_MONOTONIC:
                        s->enabled = m;
                        prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
                        prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_REALTIME:
                        s->enabled = m;
                        prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
                        prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
                        break;

                case SOURCE_SIGNAL:
                        s->enabled = m;

                        if (s->signal.sig != SIGCHLD || s->event->n_enabled_child_sources == 0)  {
                                assert_se(sigaddset(&s->event->sigset, s->signal.sig) == 0);
                                event_update_signal_fd(s->event);
                        }
                        break;

                case SOURCE_CHILD:
                        if (s->enabled == SD_EVENT_OFF) {
                                s->event->n_enabled_child_sources++;

                                if (!s->event->signal_sources || !s->event->signal_sources[SIGCHLD]) {
                                        assert_se(sigaddset(&s->event->sigset, SIGCHLD) == 0);
                                        event_update_signal_fd(s->event);
                                }
                        }

                        s->enabled = m;
                        break;

                case SOURCE_EXIT:
                        s->enabled = m;
                        prioq_reshuffle(s->event->exit, s, &s->exit.prioq_index);
                        break;

                case SOURCE_DEFER:
                        s->enabled = m;
                        break;

                case SOURCE_WATCHDOG:
                        assert_not_reached("Wut? I shouldn't exist.");
                }
        }

        if (s->pending)
                prioq_reshuffle(s->event->pending, s, &s->pending_index);

        if (s->prepare)
                prioq_reshuffle(s->event->prepare, s, &s->prepare_index);

        return 0;
}

_public_ int sd_event_source_get_time(sd_event_source *s, uint64_t *usec) {
        assert_return(s, -EINVAL);
        assert_return(usec, -EINVAL);
        assert_return(s->type == SOURCE_REALTIME || s->type == SOURCE_MONOTONIC, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *usec = s->time.next;
        return 0;
}

_public_ int sd_event_source_set_time(sd_event_source *s, uint64_t usec) {
        assert_return(s, -EINVAL);
        assert_return(usec != (uint64_t) -1, -EINVAL);
        assert_return(s->type == SOURCE_REALTIME || s->type == SOURCE_MONOTONIC, -EDOM);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        s->time.next = usec;

        source_set_pending(s, false);

        if (s->type == SOURCE_REALTIME) {
                prioq_reshuffle(s->event->realtime_earliest, s, &s->time.earliest_index);
                prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
        } else {
                prioq_reshuffle(s->event->monotonic_earliest, s, &s->time.earliest_index);
                prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);
        }

        return 0;
}

_public_ int sd_event_source_get_time_accuracy(sd_event_source *s, uint64_t *usec) {
        assert_return(s, -EINVAL);
        assert_return(usec, -EINVAL);
        assert_return(s->type == SOURCE_REALTIME || s->type == SOURCE_MONOTONIC, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *usec = s->time.accuracy;
        return 0;
}

_public_ int sd_event_source_set_time_accuracy(sd_event_source *s, uint64_t usec) {
        assert_return(s, -EINVAL);
        assert_return(usec != (uint64_t) -1, -EINVAL);
        assert_return(s->type == SOURCE_REALTIME || s->type == SOURCE_MONOTONIC, -EDOM);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (usec == 0)
                usec = DEFAULT_ACCURACY_USEC;

        s->time.accuracy = usec;

        source_set_pending(s, false);

        if (s->type == SOURCE_REALTIME)
                prioq_reshuffle(s->event->realtime_latest, s, &s->time.latest_index);
        else
                prioq_reshuffle(s->event->monotonic_latest, s, &s->time.latest_index);

        return 0;
}

_public_ int sd_event_source_get_child_pid(sd_event_source *s, pid_t *pid) {
        assert_return(s, -EINVAL);
        assert_return(pid, -EINVAL);
        assert_return(s->type == SOURCE_CHILD, -EDOM);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        *pid = s->child.pid;
        return 0;
}

_public_ int sd_event_source_set_prepare(sd_event_source *s, sd_event_handler_t callback) {
        int r;

        assert_return(s, -EINVAL);
        assert_return(s->type != SOURCE_EXIT, -EDOM);
        assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(s->event), -ECHILD);

        if (s->prepare == callback)
                return 0;

        if (callback && s->prepare) {
                s->prepare = callback;
                return 0;
        }

        r = prioq_ensure_allocated(&s->event->prepare, prepare_prioq_compare);
        if (r < 0)
                return r;

        s->prepare = callback;

        if (callback) {
                r = prioq_put(s->event->prepare, s, &s->prepare_index);
                if (r < 0)
                        return r;
        } else
                prioq_remove(s->event->prepare, s, &s->prepare_index);

        return 0;
}

_public_ void* sd_event_source_get_userdata(sd_event_source *s) {
        assert_return(s, NULL);

        return s->userdata;
}

_public_ void *sd_event_source_set_userdata(sd_event_source *s, void *userdata) {
        void *ret;

        assert_return(s, NULL);

        ret = s->userdata;
        s->userdata = userdata;

        return ret;
}

static usec_t sleep_between(sd_event *e, usec_t a, usec_t b) {
        usec_t c;
        assert(e);
        assert(a <= b);

        if (a <= 0)
                return 0;

        if (b <= a + 1)
                return a;

        /*
          Find a good time to wake up again between times a and b. We
          have two goals here:

          a) We want to wake up as seldom as possible, hence prefer
             later times over earlier times.

          b) But if we have to wake up, then let's make sure to
             dispatch as much as possible on the entire system.

          We implement this by waking up everywhere at the same time
          within any given minute if we can, synchronised via the
          perturbation value determined from the boot ID. If we can't,
          then we try to find the same spot in every 10s, then 1s and
          then 250ms step. Otherwise, we pick the last possible time
          to wake up.
        */

        c = (b / USEC_PER_MINUTE) * USEC_PER_MINUTE + e->perturb;
        if (c >= b) {
                if (_unlikely_(c < USEC_PER_MINUTE))
                        return b;

                c -= USEC_PER_MINUTE;
        }

        if (c >= a)
                return c;

        c = (b / (USEC_PER_SEC*10)) * (USEC_PER_SEC*10) + (e->perturb % (USEC_PER_SEC*10));
        if (c >= b) {
                if (_unlikely_(c < USEC_PER_SEC*10))
                        return b;

                c -= USEC_PER_SEC*10;
        }

        if (c >= a)
                return c;

        c = (b / USEC_PER_SEC) * USEC_PER_SEC + (e->perturb % USEC_PER_SEC);
        if (c >= b) {
                if (_unlikely_(c < USEC_PER_SEC))
                        return b;

                c -= USEC_PER_SEC;
        }

        if (c >= a)
                return c;

        c = (b / (USEC_PER_MSEC*250)) * (USEC_PER_MSEC*250) + (e->perturb % (USEC_PER_MSEC*250));
        if (c >= b) {
                if (_unlikely_(c < USEC_PER_MSEC*250))
                        return b;

                c -= USEC_PER_MSEC*250;
        }

        if (c >= a)
                return c;

        return b;
}

static int event_arm_timer(
                sd_event *e,
                int timer_fd,
                Prioq *earliest,
                Prioq *latest,
                usec_t *next) {

        struct itimerspec its = {};
        sd_event_source *a, *b;
        usec_t t;
        int r;

        assert(e);
        assert(next);

        a = prioq_peek(earliest);
        if (!a || a->enabled == SD_EVENT_OFF) {

                if (timer_fd < 0)
                        return 0;

                if (*next == (usec_t) -1)
                        return 0;

                /* disarm */
                r = timerfd_settime(timer_fd, TFD_TIMER_ABSTIME, &its, NULL);
                if (r < 0)
                        return r;

                *next = (usec_t) -1;

                return 0;
        }

        b = prioq_peek(latest);
        assert_se(b && b->enabled != SD_EVENT_OFF);

        t = sleep_between(e, a->time.next, b->time.next + b->time.accuracy);
        if (*next == t)
                return 0;

        assert_se(timer_fd >= 0);

        if (t == 0) {
                /* We don' want to disarm here, just mean some time looooong ago. */
                its.it_value.tv_sec = 0;
                its.it_value.tv_nsec = 1;
        } else
                timespec_store(&its.it_value, t);

        r = timerfd_settime(timer_fd, TFD_TIMER_ABSTIME, &its, NULL);
        if (r < 0)
                return -errno;

        *next = t;
        return 0;
}

static int process_io(sd_event *e, sd_event_source *s, uint32_t revents) {
        assert(e);
        assert(s);
        assert(s->type == SOURCE_IO);

        /* If the event source was already pending, we just OR in the
         * new revents, otherwise we reset the value. The ORing is
         * necessary to handle EPOLLONESHOT events properly where
         * readability might happen independently of writability, and
         * we need to keep track of both */

        if (s->pending)
                s->io.revents |= revents;
        else
                s->io.revents = revents;

        return source_set_pending(s, true);
}

static int flush_timer(sd_event *e, int fd, uint32_t events, usec_t *next) {
        uint64_t x;
        ssize_t ss;

        assert(e);
        assert(fd >= 0);

        assert_return(events == EPOLLIN, -EIO);

        ss = read(fd, &x, sizeof(x));
        if (ss < 0) {
                if (errno == EAGAIN || errno == EINTR)
                        return 0;

                return -errno;
        }

        if (_unlikely_(ss != sizeof(x)))
                return -EIO;

        if (next)
                *next = (usec_t) -1;

        return 0;
}

static int process_timer(
                sd_event *e,
                usec_t n,
                Prioq *earliest,
                Prioq *latest) {

        sd_event_source *s;
        int r;

        assert(e);

        for (;;) {
                s = prioq_peek(earliest);
                if (!s ||
                    s->time.next > n ||
                    s->enabled == SD_EVENT_OFF ||
                    s->pending)
                        break;

                r = source_set_pending(s, true);
                if (r < 0)
                        return r;

                prioq_reshuffle(earliest, s, &s->time.earliest_index);
                prioq_reshuffle(latest, s, &s->time.latest_index);
        }

        return 0;
}

static int process_child(sd_event *e) {
        sd_event_source *s;
        Iterator i;
        int r;

        assert(e);

        e->need_process_child = false;

        /*
           So, this is ugly. We iteratively invoke waitid() with P_PID
           + WNOHANG for each PID we wait for, instead of using
           P_ALL. This is because we only want to get child
           information of very specific child processes, and not all
           of them. We might not have processed the SIGCHLD even of a
           previous invocation and we don't want to maintain a
           unbounded *per-child* event queue, hence we really don't
           want anything flushed out of the kernel's queue that we
           don't care about. Since this is O(n) this means that if you
           have a lot of processes you probably want to handle SIGCHLD
           yourself.

           We do not reap the children here (by using WNOWAIT), this
           is only done after the event source is dispatched so that
           the callback still sees the process as a zombie.
        */

        HASHMAP_FOREACH(s, e->child_sources, i) {
                assert(s->type == SOURCE_CHILD);

                if (s->pending)
                        continue;

                if (s->enabled == SD_EVENT_OFF)
                        continue;

                zero(s->child.siginfo);
                r = waitid(P_PID, s->child.pid, &s->child.siginfo,
                           WNOHANG | (s->child.options & WEXITED ? WNOWAIT : 0) | s->child.options);
                if (r < 0)
                        return -errno;

                if (s->child.siginfo.si_pid != 0) {
                        bool zombie =
                                s->child.siginfo.si_code == CLD_EXITED ||
                                s->child.siginfo.si_code == CLD_KILLED ||
                                s->child.siginfo.si_code == CLD_DUMPED;

                        if (!zombie && (s->child.options & WEXITED)) {
                                /* If the child isn't dead then let's
                                 * immediately remove the state change
                                 * from the queue, since there's no
                                 * benefit in leaving it queued */

                                assert(s->child.options & (WSTOPPED|WCONTINUED));
                                waitid(P_PID, s->child.pid, &s->child.siginfo, WNOHANG|(s->child.options & (WSTOPPED|WCONTINUED)));
                        }

                        r = source_set_pending(s, true);
                        if (r < 0)
                                return r;
                }
        }

        return 0;
}

static int process_signal(sd_event *e, uint32_t events) {
        bool read_one = false;
        int r;

        assert(e);
        assert(e->signal_sources);

        assert_return(events == EPOLLIN, -EIO);

        for (;;) {
                struct signalfd_siginfo si;
                ssize_t ss;
                sd_event_source *s;

                ss = read(e->signal_fd, &si, sizeof(si));
                if (ss < 0) {
                        if (errno == EAGAIN || errno == EINTR)
                                return read_one;

                        return -errno;
                }

                if (_unlikely_(ss != sizeof(si)))
                        return -EIO;

                read_one = true;

                s = e->signal_sources[si.ssi_signo];
                if (si.ssi_signo == SIGCHLD) {
                        r = process_child(e);
                        if (r < 0)
                                return r;
                        if (r > 0 || !s)
                                continue;
                } else
                        if (!s)
                                return -EIO;

                s->signal.siginfo = si;
                r = source_set_pending(s, true);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int source_dispatch(sd_event_source *s) {
        int r = 0;

        assert(s);
        assert(s->pending || s->type == SOURCE_EXIT);

        if (s->type != SOURCE_DEFER && s->type != SOURCE_EXIT) {
                r = source_set_pending(s, false);
                if (r < 0)
                        return r;
        }

        if (s->enabled == SD_EVENT_ONESHOT) {
                r = sd_event_source_set_enabled(s, SD_EVENT_OFF);
                if (r < 0)
                        return r;
        }

        s->dispatching = true;

        switch (s->type) {

        case SOURCE_IO:
                r = s->io.callback(s, s->io.fd, s->io.revents, s->userdata);
                break;

        case SOURCE_MONOTONIC:
                r = s->time.callback(s, s->time.next, s->userdata);
                break;

        case SOURCE_REALTIME:
                r = s->time.callback(s, s->time.next, s->userdata);
                break;

        case SOURCE_SIGNAL:
                r = s->signal.callback(s, &s->signal.siginfo, s->userdata);
                break;

        case SOURCE_CHILD: {
                bool zombie;

                zombie = s->child.siginfo.si_code == CLD_EXITED ||
                         s->child.siginfo.si_code == CLD_KILLED ||
                         s->child.siginfo.si_code == CLD_DUMPED;

                r = s->child.callback(s, &s->child.siginfo, s->userdata);

                /* Now, reap the PID for good. */
                if (zombie)
                        waitid(P_PID, s->child.pid, &s->child.siginfo, WNOHANG|WEXITED);

                break;
        }

        case SOURCE_DEFER:
                r = s->defer.callback(s, s->userdata);
                break;

        case SOURCE_EXIT:
                r = s->exit.callback(s, s->userdata);
                break;

        case SOURCE_WATCHDOG:
                assert_not_reached("Wut? I shouldn't exist.");
        }

        s->dispatching = false;

        if (r < 0)
                log_debug("Event source %p returned error, disabling: %s", s, strerror(-r));

        if (s->n_ref == 0)
                source_free(s);
        else if (r < 0)
                sd_event_source_set_enabled(s, SD_EVENT_OFF);

        return 1;
}

static int event_prepare(sd_event *e) {
        int r;

        assert(e);

        for (;;) {
                sd_event_source *s;

                s = prioq_peek(e->prepare);
                if (!s || s->prepare_iteration == e->iteration || s->enabled == SD_EVENT_OFF)
                        break;

                s->prepare_iteration = e->iteration;
                r = prioq_reshuffle(e->prepare, s, &s->prepare_index);
                if (r < 0)
                        return r;

                assert(s->prepare);

                s->dispatching = true;
                r = s->prepare(s, s->userdata);
                s->dispatching = false;

                if (r < 0)
                        log_debug("Prepare callback of event source %p returned error, disabling: %s", s, strerror(-r));

                if (s->n_ref == 0)
                        source_free(s);
                else if (r < 0)
                        sd_event_source_set_enabled(s, SD_EVENT_OFF);
        }

        return 0;
}

static int dispatch_exit(sd_event *e) {
        sd_event_source *p;
        int r;

        assert(e);

        p = prioq_peek(e->exit);
        if (!p || p->enabled == SD_EVENT_OFF) {
                e->state = SD_EVENT_FINISHED;
                return 0;
        }

        sd_event_ref(e);
        e->iteration++;
        e->state = SD_EVENT_EXITING;

        r = source_dispatch(p);

        e->state = SD_EVENT_PASSIVE;
        sd_event_unref(e);

        return r;
}

static sd_event_source* event_next_pending(sd_event *e) {
        sd_event_source *p;

        assert(e);

        p = prioq_peek(e->pending);
        if (!p)
                return NULL;

        if (p->enabled == SD_EVENT_OFF)
                return NULL;

        return p;
}

static int arm_watchdog(sd_event *e) {
        struct itimerspec its = {};
        usec_t t;
        int r;

        assert(e);
        assert(e->watchdog_fd >= 0);

        t = sleep_between(e,
                          e->watchdog_last + (e->watchdog_period / 2),
                          e->watchdog_last + (e->watchdog_period * 3 / 4));

        timespec_store(&its.it_value, t);

        r = timerfd_settime(e->watchdog_fd, TFD_TIMER_ABSTIME, &its, NULL);
        if (r < 0)
                return -errno;

        return 0;
}

static int process_watchdog(sd_event *e) {
        assert(e);

        if (!e->watchdog)
                return 0;

        /* Don't notify watchdog too often */
        if (e->watchdog_last + e->watchdog_period / 4 > e->timestamp.monotonic)
                return 0;

        sd_notify(false, "WATCHDOG=1");
        e->watchdog_last = e->timestamp.monotonic;

        return arm_watchdog(e);
}

_public_ int sd_event_run(sd_event *e, uint64_t timeout) {
        struct epoll_event *ev_queue;
        unsigned ev_queue_max;
        sd_event_source *p;
        int r, i, m;

        assert_return(e, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(e->state == SD_EVENT_PASSIVE, -EBUSY);

        if (e->exit_requested)
                return dispatch_exit(e);

        sd_event_ref(e);
        e->iteration++;
        e->state = SD_EVENT_RUNNING;

        r = event_prepare(e);
        if (r < 0)
                goto finish;

        r = event_arm_timer(e, e->monotonic_fd, e->monotonic_earliest, e->monotonic_latest, &e->monotonic_next);
        if (r < 0)
                goto finish;

        r = event_arm_timer(e, e->realtime_fd, e->realtime_earliest, e->realtime_latest, &e->realtime_next);
        if (r < 0)
                goto finish;

        if (event_next_pending(e) || e->need_process_child)
                timeout = 0;
        ev_queue_max = CLAMP(e->n_sources, 1U, EPOLL_QUEUE_MAX);
        ev_queue = newa(struct epoll_event, ev_queue_max);

        m = epoll_wait(e->epoll_fd, ev_queue, ev_queue_max,
                       timeout == (uint64_t) -1 ? -1 : (int) ((timeout + USEC_PER_MSEC - 1) / USEC_PER_MSEC));
        if (m < 0) {
                r = errno == EAGAIN || errno == EINTR ? 1 : -errno;
                goto finish;
        }

        dual_timestamp_get(&e->timestamp);

        for (i = 0; i < m; i++) {

                if (ev_queue[i].data.ptr == INT_TO_PTR(SOURCE_MONOTONIC))
                        r = flush_timer(e, e->monotonic_fd, ev_queue[i].events, &e->monotonic_next);
                else if (ev_queue[i].data.ptr == INT_TO_PTR(SOURCE_REALTIME))
                        r = flush_timer(e, e->realtime_fd, ev_queue[i].events, &e->realtime_next);
                else if (ev_queue[i].data.ptr == INT_TO_PTR(SOURCE_SIGNAL))
                        r = process_signal(e, ev_queue[i].events);
                else if (ev_queue[i].data.ptr == INT_TO_PTR(SOURCE_WATCHDOG))
                        r = flush_timer(e, e->watchdog_fd, ev_queue[i].events, NULL);
                else
                        r = process_io(e, ev_queue[i].data.ptr, ev_queue[i].events);

                if (r < 0)
                        goto finish;
        }

        r = process_watchdog(e);
        if (r < 0)
                goto finish;

        r = process_timer(e, e->timestamp.monotonic, e->monotonic_earliest, e->monotonic_latest);
        if (r < 0)
                goto finish;

        r = process_timer(e, e->timestamp.realtime, e->realtime_earliest, e->realtime_latest);
        if (r < 0)
                goto finish;

        if (e->need_process_child) {
                r = process_child(e);
                if (r < 0)
                        goto finish;
        }

        p = event_next_pending(e);
        if (!p) {
                r = 1;
                goto finish;
        }

        r = source_dispatch(p);

finish:
        e->state = SD_EVENT_PASSIVE;
        sd_event_unref(e);

        return r;
}

_public_ int sd_event_loop(sd_event *e) {
        int r;

        assert_return(e, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);
        assert_return(e->state == SD_EVENT_PASSIVE, -EBUSY);

        sd_event_ref(e);

        while (e->state != SD_EVENT_FINISHED) {
                r = sd_event_run(e, (uint64_t) -1);
                if (r < 0)
                        goto finish;
        }

        r = e->exit_code;

finish:
        sd_event_unref(e);
        return r;
}

_public_ int sd_event_get_state(sd_event *e) {
        assert_return(e, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);

        return e->state;
}

_public_ int sd_event_get_exit_code(sd_event *e, int *code) {
        assert_return(e, -EINVAL);
        assert_return(code, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);

        if (!e->exit_requested)
                return -ENODATA;

        *code = e->exit_code;
        return 0;
}

_public_ int sd_event_exit(sd_event *e, int code) {
        assert_return(e, -EINVAL);
        assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
        assert_return(!event_pid_changed(e), -ECHILD);

        e->exit_requested = true;
        e->exit_code = code;

        return 0;
}

_public_ int sd_event_get_now_realtime(sd_event *e, uint64_t *usec) {
        assert_return(e, -EINVAL);
        assert_return(usec, -EINVAL);
        assert_return(dual_timestamp_is_set(&e->timestamp), -ENODATA);
        assert_return(!event_pid_changed(e), -ECHILD);

        *usec = e->timestamp.realtime;
        return 0;
}

_public_ int sd_event_get_now_monotonic(sd_event *e, uint64_t *usec) {
        assert_return(e, -EINVAL);
        assert_return(usec, -EINVAL);
        assert_return(dual_timestamp_is_set(&e->timestamp), -ENODATA);
        assert_return(!event_pid_changed(e), -ECHILD);

        *usec = e->timestamp.monotonic;
        return 0;
}

_public_ int sd_event_default(sd_event **ret) {

        static thread_local sd_event *default_event = NULL;
        sd_event *e = NULL;
        int r;

        if (!ret)
                return !!default_event;

        if (default_event) {
                *ret = sd_event_ref(default_event);
                return 0;
        }

        r = sd_event_new(&e);
        if (r < 0)
                return r;

        e->default_event_ptr = &default_event;
        e->tid = gettid();
        default_event = e;

        *ret = e;
        return 1;
}

_public_ int sd_event_get_tid(sd_event *e, pid_t *tid) {
        assert_return(e, -EINVAL);
        assert_return(tid, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);

        if (e->tid != 0) {
                *tid = e->tid;
                return 0;
        }

        return -ENXIO;
}

_public_ int sd_event_set_watchdog(sd_event *e, int b) {
        int r;

        assert_return(e, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);

        if (e->watchdog == !!b)
                return e->watchdog;

        if (b) {
                struct epoll_event ev = {};

                r = sd_watchdog_enabled(false, &e->watchdog_period);
                if (r <= 0)
                        return r;

                /* Issue first ping immediately */
                sd_notify(false, "WATCHDOG=1");
                e->watchdog_last = now(CLOCK_MONOTONIC);

                e->watchdog_fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK|TFD_CLOEXEC);
                if (e->watchdog_fd < 0)
                        return -errno;

                r = arm_watchdog(e);
                if (r < 0)
                        goto fail;

                ev.events = EPOLLIN;
                ev.data.ptr = INT_TO_PTR(SOURCE_WATCHDOG);

                r = epoll_ctl(e->epoll_fd, EPOLL_CTL_ADD, e->watchdog_fd, &ev);
                if (r < 0) {
                        r = -errno;
                        goto fail;
                }

        } else {
                if (e->watchdog_fd >= 0) {
                        epoll_ctl(e->epoll_fd, EPOLL_CTL_DEL, e->watchdog_fd, NULL);
                        close_nointr_nofail(e->watchdog_fd);
                        e->watchdog_fd = -1;
                }
        }

        e->watchdog = !!b;
        return e->watchdog;

fail:
        close_nointr_nofail(e->watchdog_fd);
        e->watchdog_fd = -1;
        return r;
}

_public_ int sd_event_get_watchdog(sd_event *e) {
        assert_return(e, -EINVAL);
        assert_return(!event_pid_changed(e), -ECHILD);

        return e->watchdog;
}
