bus: add minimal event loop API

So far we tried to use epoll directly wherever we needed an event loop.
However, that has various shortcomings, such as the inability to handle
larger amounts of timers (since each timerfd costs one fd, which is a
very limited resource, usually bounded to 1024), and inability to do
priorisation between multiple queued events.

Let's add a minimal event loop API around epoll that is suitable for
implementation of our own daemons and maybe one day can become public
API for those who desire it.

This loop is part of libsystemd-bus, but may be used independently of
it.

1 files changed, 197 insertions, 0 deletions

diff --git a/src/libsystemd-bus/test-event.c b/src/libsystemd-bus/test-event.c
new file mode 100644
index 0000000000..8dd47fe8a9
--- /dev/null
+++ b/src/libsystemd-bus/test-event.c
@@ -0,0 +1,197 @@
+/*-*- 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 "sd-event.h"
+#include "log.h"
+#include "util.h"
+
+static int prepare_handler(sd_event_source *s, void *userdata) {
+        log_info("preparing %c", PTR_TO_INT(userdata));
+        return 1;
+}
+
+static bool got_a, got_b, got_c;
+
+static int io_handler(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+
+        log_info("got IO on %c", PTR_TO_INT(userdata));
+
+        if (userdata == INT_TO_PTR('a')) {
+                assert_se(sd_event_source_set_mute(s, SD_EVENT_MUTED) >= 0);
+                assert_se(!got_a);
+                got_a = true;
+        } else if (userdata == INT_TO_PTR('b')) {
+                assert_se(!got_b);
+                got_b = true;
+        } else
+                assert_not_reached("Yuck!");
+
+        return 1;
+}
+
+static int child_handler(sd_event_source *s, const siginfo_t *si, void *userdata) {
+
+        assert(s);
+        assert(si);
+
+        log_info("got child on %c", PTR_TO_INT(userdata));
+
+        assert(userdata == INT_TO_PTR('f'));
+
+        assert_se(sd_event_request_quit(sd_event_get(s)) >= 0);
+        sd_event_source_unref(s);
+
+        return 1;
+}
+
+static int signal_handler(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) {
+        sd_event_source *p;
+        sigset_t ss;
+        pid_t pid;
+
+        assert(s);
+        assert(si);
+
+        log_info("got signal on %c", PTR_TO_INT(userdata));
+
+        assert(userdata == INT_TO_PTR('e'));
+
+        assert_se(sigemptyset(&ss) >= 0);
+        assert_se(sigaddset(&ss, SIGCHLD) >= 0);
+        assert_se(sigprocmask(SIG_BLOCK, &ss, NULL) >= 0);
+
+        pid = fork();
+        assert_se(pid >= 0);
+
+        if (pid == 0)
+                _exit(0);
+
+        assert_se(sd_event_add_child(sd_event_get(s), pid, WEXITED, child_handler, INT_TO_PTR('f'), &p) >= 0);
+        assert_se(sd_event_source_set_mute(p, SD_EVENT_ONESHOT) >= 0);
+
+        sd_event_source_unref(s);
+
+        return 1;
+}
+
+static int defer_handler(sd_event_source *s, void *userdata) {
+        sd_event_source *p;
+        sigset_t ss;
+
+        assert(s);
+
+        log_info("got defer on %c", PTR_TO_INT(userdata));
+
+        assert(userdata == INT_TO_PTR('d'));
+
+        assert_se(sigemptyset(&ss) >= 0);
+        assert_se(sigaddset(&ss, SIGUSR1) >= 0);
+        assert_se(sigprocmask(SIG_BLOCK, &ss, NULL) >= 0);
+        assert_se(sd_event_add_signal(sd_event_get(s), SIGUSR1, signal_handler, INT_TO_PTR('e'), &p) >= 0);
+        assert_se(sd_event_source_set_mute(p, SD_EVENT_ONESHOT) >= 0);
+        raise(SIGUSR1);
+
+        sd_event_source_unref(s);
+
+        return 1;
+}
+
+static bool do_quit = false;
+
+static int time_handler(sd_event_source *s, uint64_t usec, void *userdata) {
+        log_info("got timer on %c", PTR_TO_INT(userdata));
+
+        if (userdata == INT_TO_PTR('c')) {
+
+                if (do_quit) {
+                        sd_event_source *p;
+
+                        assert_se(sd_event_add_defer(sd_event_get(s), defer_handler, INT_TO_PTR('d'), &p) >= 0);
+                        assert_se(sd_event_source_set_mute(p, SD_EVENT_ONESHOT) >= 0);
+                } else {
+                        assert(!got_c);
+                        got_c = true;
+                }
+        } else
+                assert_not_reached("Huh?");
+
+        return 2;
+}
+
+int main(int argc, char *argv[]) {
+        sd_event *e = NULL;
+        sd_event_source *x = NULL, *y = NULL, *z = NULL;
+        static const char ch = 'x';
+        int a[2] = { -1, -1 }, b[2] = { -1, -1};
+
+        assert_se(pipe(a) >= 0);
+        assert_se(pipe(b) >= 0);
+
+        assert_se(sd_event_new(&e) >= 0);
+
+        got_a = false, got_b = false, got_c = false;
+
+        assert_se(sd_event_add_io(e, a[0], EPOLLIN, io_handler, INT_TO_PTR('a'), &x) >= 0);
+        assert_se(sd_event_add_io(e, b[0], EPOLLIN, io_handler, INT_TO_PTR('b'), &y) >= 0);
+        assert_se(sd_event_add_monotonic(e, 0, time_handler, INT_TO_PTR('c'), &z) >= 0);
+
+        assert_se(sd_event_source_set_priority(x, 99) >= 0);
+        assert_se(sd_event_source_set_mute(y, SD_EVENT_ONESHOT) >= 0);
+        assert_se(sd_event_source_set_prepare(x, prepare_handler) >= 0);
+        assert_se(sd_event_source_set_priority(z, 50) >= 0);
+        assert_se(sd_event_source_set_mute(z, SD_EVENT_ONESHOT) >= 0);
+        assert_se(sd_event_source_set_prepare(z, prepare_handler) >= 0);
+
+        assert_se(write(a[1], &ch, 1) >= 0);
+        assert_se(write(b[1], &ch, 1) >= 0);
+
+        assert_se(!got_a && !got_b && !got_c);
+
+        assert_se(sd_event_run(e, (uint64_t) -1) >= 1);
+
+        assert_se(!got_a && got_b && !got_c);
+
+        assert_se(sd_event_run(e, (uint64_t) -1) >= 1);
+
+        assert_se(!got_a && got_b && got_c);
+
+        assert_se(sd_event_run(e, (uint64_t) -1) >= 1);
+
+        assert_se(got_a && got_b && got_c);
+
+        sd_event_source_unref(x);
+        sd_event_source_unref(y);
+
+        do_quit = true;
+        assert_se(sd_event_source_set_time(z, now(CLOCK_MONOTONIC) + 200 * USEC_PER_MSEC) >= 0);
+        assert_se(sd_event_source_set_mute(z, SD_EVENT_ONESHOT) >= 0);
+
+        assert_se(sd_event_loop(e) >= 0);
+
+        sd_event_source_unref(z);
+
+        sd_event_unref(e);
+
+        close_pipe(a);
+        close_pipe(b);
+
+        return 0;
+}