From 94eb0858c2b938549d9d1703c872c6149901e7dd Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Sat, 19 Jun 2021 20:50:18 +0200
Subject: Converting the former BFD loop to a universal IO loop and protocol
 loop.

There is a simple universal IO loop, taking care of events, timers and
sockets. Primarily, one instance of a protocol should use exactly one IO
loop to do all its work, as is now done in BFD.

Contrary to previous versions, the loop is now launched and cleaned by
the nest/proto.c code, allowing for a protocol to just request its own
loop by setting the loop's lock order in config higher than the_bird.

It is not supported nor checked if any protocol changed the requested
lock order in reconfigure. No protocol should do it at all.
---
 sysdep/unix/io-loop.c | 313 +++++++++++++++++++++++++++-----------------------
 1 file changed, 170 insertions(+), 143 deletions(-)

(limited to 'sysdep/unix/io-loop.c')

diff --git a/sysdep/unix/io-loop.c b/sysdep/unix/io-loop.c
index a15d866a..275d38a0 100644
--- a/sysdep/unix/io-loop.c
+++ b/sysdep/unix/io-loop.c
@@ -15,50 +15,47 @@
 #include <sys/time.h>
 
 #include "nest/bird.h"
-#include "sysdep/unix/io-loop.h"
 
 #include "lib/buffer.h"
+#include "lib/coro.h"
 #include "lib/lists.h"
 #include "lib/resource.h"
 #include "lib/event.h"
 #include "lib/timer.h"
 #include "lib/socket.h"
 
-
-struct birdloop
-{
-  pool *pool;
-  pthread_t thread;
-  pthread_mutex_t mutex;
-
-  u8 stop_called;
-  u8 poll_active;
-  u8 wakeup_masked;
-  int wakeup_fds[2];
-
-  struct timeloop time;
-  list event_list;
-  list sock_list;
-  uint sock_num;
-
-  BUFFER(sock *) poll_sk;
-  BUFFER(struct pollfd) poll_fd;
-  u8 poll_changed;
-  u8 close_scheduled;
-};
-
+#include "lib/io-loop.h"
+#include "sysdep/unix/io-loop.h"
+#include "conf/conf.h"
 
 /*
  *	Current thread context
  */
 
-static _Thread_local struct birdloop *birdloop_current;
+_Thread_local struct birdloop *birdloop_current;
+static _Thread_local struct birdloop *birdloop_wakeup_masked;
+static _Thread_local uint birdloop_wakeup_masked_count;
 
-static inline void
-birdloop_set_current(struct birdloop *loop)
+event_list *
+birdloop_event_list(struct birdloop *loop)
 {
-  birdloop_current = loop;
-  local_timeloop = loop ? &loop->time : &main_timeloop;
+  return &loop->event_list;
+}
+
+struct timeloop *
+birdloop_time_loop(struct birdloop *loop)
+{
+  return &loop->time;
+}
+
+_Bool
+birdloop_inside(struct birdloop *loop)
+{
+  for (struct birdloop *c = birdloop_current; c; c = c->prev_loop)
+    if (loop == c)
+      return 1;
+
+  return 0;
 }
 
 /*
@@ -135,57 +132,17 @@ wakeup_do_kick(struct birdloop *loop)
   pipe_kick(loop->wakeup_fds[1]);
 }
 
-static inline void
-wakeup_kick(struct birdloop *loop)
-{
-  if (!loop->wakeup_masked)
-    wakeup_do_kick(loop);
-  else
-    loop->wakeup_masked = 2;
-}
-
-/* For notifications from outside */
 void
-wakeup_kick_current(void)
+birdloop_ping(struct birdloop *loop)
 {
-  if (birdloop_current && birdloop_current->poll_active)
-    wakeup_kick(birdloop_current);
-}
-
-
-/*
- *	Events
- */
+  u32 ping_sent = atomic_fetch_add_explicit(&loop->ping_sent, 1, memory_order_acq_rel);
+  if (ping_sent)
+    return;
 
-static inline uint
-events_waiting(struct birdloop *loop)
-{
-  return !EMPTY_LIST(loop->event_list);
-}
-
-static inline void
-events_init(struct birdloop *loop)
-{
-  init_list(&loop->event_list);
-}
-
-static void
-events_fire(struct birdloop *loop)
-{
-  times_update();
-  ev_run_list(&loop->event_list);
-}
-
-void
-ev2_schedule(event *e)
-{
-  if (birdloop_current->poll_active && EMPTY_LIST(birdloop_current->event_list))
-    wakeup_kick(birdloop_current);
-
-  if (e->n.next)
-    rem_node(&e->n);
-
-  add_tail(&birdloop_current->event_list, &e->n);
+  if (loop == birdloop_wakeup_masked)
+    birdloop_wakeup_masked_count++;
+  else
+    wakeup_do_kick(loop);
 }
 
 
@@ -213,13 +170,13 @@ sockets_add(struct birdloop *loop, sock *s)
   s->index = -1;
   loop->poll_changed = 1;
 
-  if (loop->poll_active)
-    wakeup_kick(loop);
+  birdloop_ping(loop);
 }
 
 void
 sk_start(sock *s)
 {
+  ASSERT_DIE(birdloop_current != &main_birdloop);
   sockets_add(birdloop_current, s);
 }
 
@@ -230,28 +187,21 @@ sockets_remove(struct birdloop *loop, sock *s)
   loop->sock_num--;
 
   if (s->index >= 0)
+  {
     loop->poll_sk.data[s->index] = NULL;
-
-  s->index = -1;
-  loop->poll_changed = 1;
-
-  /* Wakeup moved to sk_stop() */
+    s->index = -1;
+    loop->poll_changed = 1;
+    loop->close_scheduled = 1;
+    birdloop_ping(loop);
+  }
+  else
+    close(s->fd);
 }
 
 void
 sk_stop(sock *s)
 {
   sockets_remove(birdloop_current, s);
-
-  if (birdloop_current->poll_active)
-  {
-    birdloop_current->close_scheduled = 1;
-    wakeup_kick(birdloop_current);
-  }
-  else
-    close(s->fd);
-
-  s->fd = -1;
 }
 
 static inline uint sk_want_events(sock *s)
@@ -351,12 +301,15 @@ sockets_fire(struct birdloop *loop)
 
     if (pfd->revents & POLLIN)
       while (e && *psk && (*psk)->rx_hook)
-	e = sk_read(*psk, 0);
+	e = sk_read(*psk, pfd->revents);
 
     e = 1;
     if (pfd->revents & POLLOUT)
+    {
+      loop->poll_changed = 1;
       while (e && *psk)
 	e = sk_write(*psk);
+    }
   }
 }
 
@@ -365,104 +318,168 @@ sockets_fire(struct birdloop *loop)
  *	Birdloop
  */
 
-static void *birdloop_main(void *arg);
+struct birdloop main_birdloop;
+
+static void birdloop_enter_locked(struct birdloop *loop);
+
+void
+birdloop_init(void)
+{
+  wakeup_init(&main_birdloop);
+
+  main_birdloop.time.domain = the_bird_domain.the_bird;
+  main_birdloop.time.loop = &main_birdloop;
+
+  times_update();
+  timers_init(&main_birdloop.time, &root_pool);
+
+  birdloop_enter_locked(&main_birdloop);
+}
+
+static void birdloop_main(void *arg);
 
 struct birdloop *
-birdloop_new(void)
+birdloop_new(pool *pp, uint order, const char *name)
 {
-  pool *p = rp_new(NULL, "Birdloop root");
+  struct domain_generic *dg = domain_new(name, order);
+
+  pool *p = rp_new(pp, name);
   struct birdloop *loop = mb_allocz(p, sizeof(struct birdloop));
   loop->pool = p;
-  pthread_mutex_init(&loop->mutex, NULL);
 
-  wakeup_init(loop);
+  loop->time.domain = dg;
+  loop->time.loop = loop;
+
+  birdloop_enter(loop);
 
-  events_init(loop);
+  wakeup_init(loop);
+  ev_init_list(&loop->event_list, loop, name);
   timers_init(&loop->time, p);
   sockets_init(loop);
 
+  loop->time.coro = coro_run(p, birdloop_main, loop);
+
+  birdloop_leave(loop);
+
   return loop;
 }
 
+static void
+birdloop_do_stop(struct birdloop *loop, void (*stopped)(void *data), void *data)
+{
+  loop->stopped = stopped;
+  loop->stop_data = data;
+  wakeup_do_kick(loop);
+}
+
 void
-birdloop_start(struct birdloop *loop)
+birdloop_stop(struct birdloop *loop, void (*stopped)(void *data), void *data)
 {
-  int rv = pthread_create(&loop->thread, NULL, birdloop_main, loop);
-  if (rv)
-    die("pthread_create(): %M", rv);
+  DG_LOCK(loop->time.domain);
+  birdloop_do_stop(loop, stopped, data);
+  DG_UNLOCK(loop->time.domain);
 }
 
 void
-birdloop_stop(struct birdloop *loop)
+birdloop_stop_self(struct birdloop *loop, void (*stopped)(void *data), void *data)
 {
-  pthread_mutex_lock(&loop->mutex);
-  loop->stop_called = 1;
-  wakeup_do_kick(loop);
-  pthread_mutex_unlock(&loop->mutex);
+  ASSERT_DIE(loop == birdloop_current);
+  ASSERT_DIE(DG_IS_LOCKED(loop->time.domain));
 
-  int rv = pthread_join(loop->thread, NULL);
-  if (rv)
-    die("pthread_join(): %M", rv);
+  birdloop_do_stop(loop, stopped, data);
 }
 
 void
 birdloop_free(struct birdloop *loop)
 {
+  ASSERT_DIE(loop->links == 0);
+  domain_free(loop->time.domain);
   rfree(loop->pool);
 }
 
+static void
+birdloop_enter_locked(struct birdloop *loop)
+{
+  ASSERT_DIE(DG_IS_LOCKED(loop->time.domain));
+  ASSERT_DIE(!birdloop_inside(loop));
+
+  /* Store the old context */
+  loop->prev_loop = birdloop_current;
+
+  /* Put the new context */
+  birdloop_current = loop;
+}
 
 void
 birdloop_enter(struct birdloop *loop)
 {
-  /* TODO: these functions could save and restore old context */
-  pthread_mutex_lock(&loop->mutex);
-  birdloop_set_current(loop);
+  DG_LOCK(loop->time.domain);
+  return birdloop_enter_locked(loop);
+}
+
+static void
+birdloop_leave_locked(struct birdloop *loop)
+{
+  /* Check the current context */
+  ASSERT_DIE(birdloop_current == loop);
+
+  /* Restore the old context */
+  birdloop_current = loop->prev_loop;
 }
 
 void
 birdloop_leave(struct birdloop *loop)
 {
-  /* TODO: these functions could save and restore old context */
-  birdloop_set_current(NULL);
-  pthread_mutex_unlock(&loop->mutex);
+  birdloop_leave_locked(loop);
+  DG_UNLOCK(loop->time.domain);
 }
 
 void
 birdloop_mask_wakeups(struct birdloop *loop)
 {
-  pthread_mutex_lock(&loop->mutex);
-  loop->wakeup_masked = 1;
-  pthread_mutex_unlock(&loop->mutex);
+  ASSERT_DIE(birdloop_wakeup_masked == NULL);
+  birdloop_wakeup_masked = loop;
 }
 
 void
 birdloop_unmask_wakeups(struct birdloop *loop)
 {
-  pthread_mutex_lock(&loop->mutex);
-  if (loop->wakeup_masked == 2)
+  ASSERT_DIE(birdloop_wakeup_masked == loop);
+  birdloop_wakeup_masked = NULL;
+  if (birdloop_wakeup_masked_count)
     wakeup_do_kick(loop);
-  loop->wakeup_masked = 0;
-  pthread_mutex_unlock(&loop->mutex);
+
+  birdloop_wakeup_masked_count = 0;
 }
 
-static void *
+void
+birdloop_link(struct birdloop *loop)
+{
+  ASSERT_DIE(birdloop_inside(loop));
+  loop->links++;
+}
+
+void
+birdloop_unlink(struct birdloop *loop)
+{
+  ASSERT_DIE(birdloop_inside(loop));
+  loop->links--;
+}
+
+static void
 birdloop_main(void *arg)
 {
   struct birdloop *loop = arg;
   timer *t;
   int rv, timeout;
 
-  birdloop_set_current(loop);
+  btime loop_begin = current_time();
 
-  pthread_mutex_lock(&loop->mutex);
+  birdloop_enter(loop);
   while (1)
   {
-    events_fire(loop);
-    timers_fire(&loop->time);
-
-    times_update();
-    if (events_waiting(loop))
+    timers_fire(&loop->time, 0);
+    if (ev_run_list(&loop->event_list))
       timeout = 0;
     else if (t = timers_first(&loop->time))
       timeout = (tm_remains(t) TO_MS) + 1;
@@ -472,8 +489,11 @@ birdloop_main(void *arg)
     if (loop->poll_changed)
       sockets_prepare(loop);
 
-    loop->poll_active = 1;
-    pthread_mutex_unlock(&loop->mutex);
+    btime duration = current_time() - loop_begin;
+    if (duration > config->watchdog_warning)
+      log(L_WARN "I/O loop cycle took %d ms", (int) (duration TO_MS));
+
+    birdloop_leave(loop);
 
   try:
     rv = poll(loop->poll_fd.data, loop->poll_fd.used, timeout);
@@ -484,25 +504,32 @@ birdloop_main(void *arg)
       die("poll: %m");
     }
 
-    pthread_mutex_lock(&loop->mutex);
-    loop->poll_active = 0;
+    birdloop_enter(loop);
 
     if (loop->close_scheduled)
       sockets_close_fds(loop);
 
-    if (loop->stop_called)
+    if (loop->stopped)
       break;
 
+    loop_begin = current_time();
+
     if (rv)
       sockets_fire(loop);
 
-    timers_fire(&loop->time);
+    atomic_exchange_explicit(&loop->ping_sent, 0, memory_order_acq_rel);
   }
 
-  loop->stop_called = 0;
-  pthread_mutex_unlock(&loop->mutex);
+  /* Flush remaining events */
+  ASSERT_DIE(!ev_run_list(&loop->event_list));
+
+  /* No timers allowed */
+  ASSERT_DIE(timers_count(&loop->time) == 0);
+  ASSERT_DIE(EMPTY_LIST(loop->sock_list));
+  ASSERT_DIE(loop->sock_num == 0);
 
-  return NULL;
+  birdloop_leave(loop);
+  loop->stopped(loop->stop_data);
 }
 
 
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