sd-event: split run into prepare/wait/dispatch

This will allow sd-event to be integrated into an external event loop, which
in turn will allow (say) glib-based applications to use our various libraries,
without manually integrating each of them (bus, rtnl, dhcp, ...).

The external event-loop should integrate sd-event int he following way:

Every iteration must start with a call to sd_event_prepare(), which will
return 0 if no event sources are ready to be processed, a positive value if
they are and a negative value on error. sd_event_prepare() may only be called
following sd_event_dispatch(); a call to sd_event_wait() indicating that no
sources are ready to be dispatched; or a failed call to sd_event_dispatch() or
sd_event_wait().

A successful call to sd_event_prepare() indicating that no event sources are
ready to be dispatched must be followed by a call to sd_event_wait(),
which will return 0 if it timed out without event sources being ready to
be processed, a negative value on error and a positive value otherwise.
sd_event_wait() may only be called following a successful call to
sd_event_prepare() indicating that no event sources are ready to be dispatched.

If sd_event_wait() indicates that some events sources are ready to be
dispatched, it must be followed by a call to sd_event_dispatch(). This
is the only time sd_event_dispatch() may be called.

2 files changed, 102 insertions, 25 deletions

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index e062997a80..a71962c24c 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -2210,12 +2210,8 @@ static int process_watchdog(sd_event *e) {
         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;
-        bool timedout;
+_public_ int sd_event_prepare(sd_event *e) {
+        int r;
 
         assert_return(e, -EINVAL);
         assert_return(!event_pid_changed(e), -ECHILD);
@@ -2223,38 +2219,60 @@ _public_ int sd_event_run(sd_event *e, uint64_t timeout) {
         assert_return(e->state == SD_EVENT_PASSIVE, -EBUSY);
 
         if (e->exit_requested)
-                return dispatch_exit(e);
+                goto pending;
 
-        sd_event_ref(e);
         e->iteration++;
-        e->state = SD_EVENT_RUNNING;
 
         r = event_prepare(e);
         if (r < 0)
-                goto finish;
+                return r;
 
         r = event_arm_timer(e, &e->realtime);
         if (r < 0)
-                goto finish;
+                return r;
 
         r = event_arm_timer(e, &e->boottime);
         if (r < 0)
-                goto finish;
+                return r;
 
         r = event_arm_timer(e, &e->monotonic);
         if (r < 0)
-                goto finish;
+                return r;
 
         r = event_arm_timer(e, &e->realtime_alarm);
         if (r < 0)
-                goto finish;
+                return r;
 
         r = event_arm_timer(e, &e->boottime_alarm);
         if (r < 0)
-                goto finish;
+                return r;
 
         if (event_next_pending(e) || e->need_process_child)
-                timeout = 0;
+                goto pending;
+
+        e->state = SD_EVENT_PREPARED;
+
+        return 0;
+
+pending:
+        e->state = SD_EVENT_PREPARED;
+        return sd_event_wait(e, 0);
+}
+
+_public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
+        struct epoll_event *ev_queue;
+        unsigned ev_queue_max;
+        int r, m, i;
+
+        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_PREPARED, -EBUSY);
+
+        if (e->exit_requested) {
+                e->state = SD_EVENT_PENDING;
+                return 1;
+        }
 
         ev_queue_max = CLAMP(e->n_sources, 1U, EPOLL_QUEUE_MAX);
         ev_queue = newa(struct epoll_event, ev_queue_max);
@@ -2262,12 +2280,16 @@ _public_ int sd_event_run(sd_event *e, uint64_t timeout) {
         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;
+                if (errno == EINTR) {
+                        e->state = SD_EVENT_PENDING;
+                        return 1;
+                }
+
+                r = -errno;
+
                 goto finish;
         }
 
-        timedout = m == 0;
-
         dual_timestamp_get(&e->timestamp);
         e->timestamp_boottime = now(CLOCK_BOOTTIME);
 
@@ -2324,21 +2346,71 @@ _public_ int sd_event_run(sd_event *e, uint64_t timeout) {
                         goto finish;
         }
 
-        p = event_next_pending(e);
-        if (!p) {
-                r = !timedout;
-                goto finish;
+        if (event_next_pending(e)) {
+                e->state = SD_EVENT_PENDING;
+
+                return 1;
         }
 
-        r = source_dispatch(p);
+        r = 0;
 
 finish:
         e->state = SD_EVENT_PASSIVE;
-        sd_event_unref(e);
 
         return r;
 }
 
+_public_ int sd_event_dispatch(sd_event *e) {
+        sd_event_source *p;
+        int r;
+
+        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_PENDING, -EBUSY);
+
+        if (e->exit_requested)
+                return dispatch_exit(e);
+
+        p = event_next_pending(e);
+        if (p) {
+                sd_event_ref(e);
+
+                e->state = SD_EVENT_RUNNING;
+                r = source_dispatch(p);
+                e->state = SD_EVENT_PASSIVE;
+
+                sd_event_unref(e);
+
+                return r;
+        }
+
+        e->state = SD_EVENT_PASSIVE;
+
+        return 1;
+}
+
+_public_ int sd_event_run(sd_event *e, uint64_t timeout) {
+        int r;
+
+        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);
+
+        r = sd_event_prepare(e);
+        if (r > 0)
+                return sd_event_dispatch(e);
+        else if (r < 0)
+                return r;
+
+        r = sd_event_wait(e, timeout);
+        if (r > 0)
+                return sd_event_dispatch(e);
+        else
+                return r;
+}
+
 _public_ int sd_event_loop(sd_event *e) {
         int r;
 
diff --git a/src/systemd/sd-event.h b/src/systemd/sd-event.h
index d96852a763..8e013b33f6 100644
--- a/src/systemd/sd-event.h
+++ b/src/systemd/sd-event.h
@@ -52,6 +52,8 @@ enum {
 
 enum {
         SD_EVENT_PASSIVE,
+        SD_EVENT_PREPARED,
+        SD_EVENT_PENDING,
         SD_EVENT_RUNNING,
         SD_EVENT_EXITING,
         SD_EVENT_FINISHED
@@ -84,6 +86,9 @@ int sd_event_add_defer(sd_event *e, sd_event_source **s, sd_event_handler_t call
 int sd_event_add_post(sd_event *e, sd_event_source **s, sd_event_handler_t callback, void *userdata);
 int sd_event_add_exit(sd_event *e, sd_event_source **s, sd_event_handler_t callback, void *userdata);
 
+int sd_event_prepare(sd_event *e);
+int sd_event_wait(sd_event *e, uint64_t timeout);
+int sd_event_dispatch(sd_event *e);
 int sd_event_run(sd_event *e, uint64_t timeout);
 int sd_event_loop(sd_event *e);
 int sd_event_exit(sd_event *e, int code);