1 files changed, 252 insertions, 68 deletions

diff --git a/src/core/lib/iomgr/timer_generic.c b/src/core/lib/iomgr/timer_generic.c
index e53c801929..d8e6068431 100644
--- a/src/core/lib/iomgr/timer_generic.c
+++ b/src/core/lib/iomgr/timer_generic.c
@@ -37,9 +37,13 @@
 
 #include "src/core/lib/iomgr/timer.h"
 
+#include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
 #include <grpc/support/sync.h>
+#include <grpc/support/tls.h>
 #include <grpc/support/useful.h>
+#include "src/core/lib/debug/trace.h"
 #include "src/core/lib/iomgr/time_averaged_stats.h"
 #include "src/core/lib/iomgr/timer_heap.h"
 #include "src/core/lib/support/spinlock.h"
@@ -52,12 +56,15 @@
 #define MIN_QUEUE_WINDOW_DURATION 0.01
 #define MAX_QUEUE_WINDOW_DURATION 1
 
+int grpc_timer_trace = 0;
+int grpc_timer_check_trace = 0;
+
 typedef struct {
   gpr_mu mu;
   grpc_time_averaged_stats stats;
   /* All and only timers with deadlines <= this will be in the heap. */
-  gpr_timespec queue_deadline_cap;
-  gpr_timespec min_deadline;
+  gpr_atm queue_deadline_cap;
+  gpr_atm min_deadline;
   /* Index in the g_shard_queue */
   uint32_t shard_queue_index;
   /* This holds all timers with deadlines < queue_deadline_cap. Timers in this
@@ -67,38 +74,92 @@ typedef struct {
   grpc_timer list;
 } shard_type;
 
-/* Protects g_shard_queue */
-static gpr_mu g_mu;
-/* Allow only one run_some_expired_timers at once */
-static gpr_spinlock g_checker_mu = GPR_SPINLOCK_STATIC_INITIALIZER;
+struct shared_mutables {
+  gpr_atm min_timer;
+  /* Allow only one run_some_expired_timers at once */
+  gpr_spinlock checker_mu;
+  bool initialized;
+  /* Protects g_shard_queue */
+  gpr_mu mu;
+} GPR_ALIGN_STRUCT(GPR_CACHELINE_SIZE);
+
+static struct shared_mutables g_shared_mutables = {
+    .checker_mu = GPR_SPINLOCK_STATIC_INITIALIZER, .initialized = false,
+};
 static gpr_clock_type g_clock_type;
 static shard_type g_shards[NUM_SHARDS];
-/* Protected by g_mu */
+/* Protected by g_shared_mutables.mu */
 static shard_type *g_shard_queue[NUM_SHARDS];
-static bool g_initialized = false;
+static gpr_timespec g_start_time;
+
+GPR_TLS_DECL(g_last_seen_min_timer);
+
+static gpr_atm saturating_add(gpr_atm a, gpr_atm b) {
+  if (a > GPR_ATM_MAX - b) {
+    return GPR_ATM_MAX;
+  }
+  return a + b;
+}
+
+static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_atm now,
+                                   gpr_atm *next, grpc_error *error);
+
+static gpr_timespec dbl_to_ts(double d) {
+  gpr_timespec ts;
+  ts.tv_sec = (int64_t)d;
+  ts.tv_nsec = (int32_t)(1e9 * (d - (double)ts.tv_sec));
+  ts.clock_type = GPR_TIMESPAN;
+  return ts;
+}
+
+static gpr_atm timespec_to_atm_round_up(gpr_timespec ts) {
+  ts = gpr_time_sub(ts, g_start_time);
+  double x = GPR_MS_PER_SEC * (double)ts.tv_sec +
+             (double)ts.tv_nsec / GPR_NS_PER_MS +
+             (double)(GPR_NS_PER_SEC - 1) / (double)GPR_NS_PER_SEC;
+  if (x < 0) return 0;
+  if (x > GPR_ATM_MAX) return GPR_ATM_MAX;
+  return (gpr_atm)x;
+}
+
+static gpr_atm timespec_to_atm_round_down(gpr_timespec ts) {
+  ts = gpr_time_sub(ts, g_start_time);
+  double x =
+      GPR_MS_PER_SEC * (double)ts.tv_sec + (double)ts.tv_nsec / GPR_NS_PER_MS;
+  if (x < 0) return 0;
+  if (x > GPR_ATM_MAX) return GPR_ATM_MAX;
+  return (gpr_atm)x;
+}
 
-static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
-                                   gpr_timespec *next, grpc_error *error);
+static gpr_timespec atm_to_timespec(gpr_atm x) {
+  return gpr_time_add(g_start_time, dbl_to_ts((double)x / 1000.0));
+}
 
-static gpr_timespec compute_min_deadline(shard_type *shard) {
+static gpr_atm compute_min_deadline(shard_type *shard) {
   return grpc_timer_heap_is_empty(&shard->heap)
-             ? shard->queue_deadline_cap
+             ? saturating_add(shard->queue_deadline_cap, 1)
              : grpc_timer_heap_top(&shard->heap)->deadline;
 }
 
 void grpc_timer_list_init(gpr_timespec now) {
   uint32_t i;
 
-  g_initialized = true;
-  gpr_mu_init(&g_mu);
+  g_shared_mutables.initialized = true;
+  gpr_mu_init(&g_shared_mutables.mu);
   g_clock_type = now.clock_type;
+  g_start_time = now;
+  g_shared_mutables.min_timer = timespec_to_atm_round_down(now);
+  gpr_tls_init(&g_last_seen_min_timer);
+  gpr_tls_set(&g_last_seen_min_timer, 0);
+  grpc_register_tracer("timer", &grpc_timer_trace);
+  grpc_register_tracer("timer_check", &grpc_timer_check_trace);
 
   for (i = 0; i < NUM_SHARDS; i++) {
     shard_type *shard = &g_shards[i];
     gpr_mu_init(&shard->mu);
     grpc_time_averaged_stats_init(&shard->stats, 1.0 / ADD_DEADLINE_SCALE, 0.1,
                                   0.5);
-    shard->queue_deadline_cap = now;
+    shard->queue_deadline_cap = g_shared_mutables.min_timer;
     shard->shard_queue_index = i;
     grpc_timer_heap_init(&shard->heap);
     shard->list.next = shard->list.prev = &shard->list;
@@ -110,29 +171,23 @@ void grpc_timer_list_init(gpr_timespec now) {
 void grpc_timer_list_shutdown(grpc_exec_ctx *exec_ctx) {
   int i;
   run_some_expired_timers(
-      exec_ctx, gpr_inf_future(g_clock_type), NULL,
+      exec_ctx, GPR_ATM_MAX, NULL,
       GRPC_ERROR_CREATE_FROM_STATIC_STRING("Timer list shutdown"));
   for (i = 0; i < NUM_SHARDS; i++) {
     shard_type *shard = &g_shards[i];
     gpr_mu_destroy(&shard->mu);
     grpc_timer_heap_destroy(&shard->heap);
   }
-  gpr_mu_destroy(&g_mu);
-  g_initialized = false;
+  gpr_mu_destroy(&g_shared_mutables.mu);
+  gpr_tls_destroy(&g_last_seen_min_timer);
+  g_shared_mutables.initialized = false;
 }
 
 static double ts_to_dbl(gpr_timespec ts) {
   return (double)ts.tv_sec + 1e-9 * ts.tv_nsec;
 }
 
-static gpr_timespec dbl_to_ts(double d) {
-  gpr_timespec ts;
-  ts.tv_sec = (int64_t)d;
-  ts.tv_nsec = (int32_t)(1e9 * (d - (double)ts.tv_sec));
-  ts.clock_type = GPR_TIMESPAN;
-  return ts;
-}
-
+/* returns true if the first element in the list */
 static void list_join(grpc_timer *head, grpc_timer *timer) {
   timer->next = head;
   timer->prev = head->prev;
@@ -158,15 +213,13 @@ static void swap_adjacent_shards_in_queue(uint32_t first_shard_queue_index) {
 
 static void note_deadline_change(shard_type *shard) {
   while (shard->shard_queue_index > 0 &&
-         gpr_time_cmp(
-             shard->min_deadline,
-             g_shard_queue[shard->shard_queue_index - 1]->min_deadline) < 0) {
+         shard->min_deadline <
+             g_shard_queue[shard->shard_queue_index - 1]->min_deadline) {
     swap_adjacent_shards_in_queue(shard->shard_queue_index - 1);
   }
   while (shard->shard_queue_index < NUM_SHARDS - 1 &&
-         gpr_time_cmp(
-             shard->min_deadline,
-             g_shard_queue[shard->shard_queue_index + 1]->min_deadline) > 0) {
+         shard->min_deadline >
+             g_shard_queue[shard->shard_queue_index + 1]->min_deadline) {
     swap_adjacent_shards_in_queue(shard->shard_queue_index);
   }
 }
@@ -179,9 +232,17 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
   GPR_ASSERT(deadline.clock_type == g_clock_type);
   GPR_ASSERT(now.clock_type == g_clock_type);
   timer->closure = closure;
-  timer->deadline = deadline;
+  timer->deadline = timespec_to_atm_round_up(deadline);
+
+  if (grpc_timer_trace) {
+    gpr_log(GPR_DEBUG, "TIMER %p: SET %" PRId64 ".%09d [%" PRIdPTR
+                       "] now %" PRId64 ".%09d [%" PRIdPTR "] call %p[%p]",
+            timer, deadline.tv_sec, deadline.tv_nsec, timer->deadline,
+            now.tv_sec, now.tv_nsec, timespec_to_atm_round_down(now), closure,
+            closure->cb);
+  }
 
-  if (!g_initialized) {
+  if (!g_shared_mutables.initialized) {
     timer->pending = false;
     grpc_closure_sched(exec_ctx, timer->closure,
                        GRPC_ERROR_CREATE_FROM_STATIC_STRING(
@@ -201,12 +262,18 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
 
   grpc_time_averaged_stats_add_sample(&shard->stats,
                                       ts_to_dbl(gpr_time_sub(deadline, now)));
-  if (gpr_time_cmp(deadline, shard->queue_deadline_cap) < 0) {
+  if (timer->deadline < shard->queue_deadline_cap) {
     is_first_timer = grpc_timer_heap_add(&shard->heap, timer);
   } else {
     timer->heap_index = INVALID_HEAP_INDEX;
     list_join(&shard->list, timer);
   }
+  if (grpc_timer_trace) {
+    gpr_log(GPR_DEBUG, "  .. add to shard %d with queue_deadline_cap=%" PRIdPTR
+                       " => is_first_timer=%s",
+            (int)(shard - g_shards), shard->queue_deadline_cap,
+            is_first_timer ? "true" : "false");
+  }
   gpr_mu_unlock(&shard->mu);
 
   /* Deadline may have decreased, we need to adjust the master queue.  Note
@@ -221,28 +288,41 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
      In that case, the timer will simply have to wait for the next
      grpc_timer_check. */
   if (is_first_timer) {
-    gpr_mu_lock(&g_mu);
-    if (gpr_time_cmp(deadline, shard->min_deadline) < 0) {
-      gpr_timespec old_min_deadline = g_shard_queue[0]->min_deadline;
-      shard->min_deadline = deadline;
+    gpr_mu_lock(&g_shared_mutables.mu);
+    if (grpc_timer_trace) {
+      gpr_log(GPR_DEBUG, "  .. old shard min_deadline=%" PRIdPTR,
+              shard->min_deadline);
+    }
+    if (timer->deadline < shard->min_deadline) {
+      gpr_atm old_min_deadline = g_shard_queue[0]->min_deadline;
+      shard->min_deadline = timer->deadline;
       note_deadline_change(shard);
-      if (shard->shard_queue_index == 0 &&
-          gpr_time_cmp(deadline, old_min_deadline) < 0) {
+      if (shard->shard_queue_index == 0 && timer->deadline < old_min_deadline) {
+        gpr_atm_no_barrier_store(&g_shared_mutables.min_timer, timer->deadline);
         grpc_kick_poller();
       }
     }
-    gpr_mu_unlock(&g_mu);
+    gpr_mu_unlock(&g_shared_mutables.mu);
   }
 }
 
+void grpc_timer_consume_kick(void) {
+  /* force re-evaluation of last seeen min */
+  gpr_tls_set(&g_last_seen_min_timer, 0);
+}
+
 void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
-  if (!g_initialized) {
+  if (!g_shared_mutables.initialized) {
     /* must have already been cancelled, also the shard mutex is invalid */
     return;
   }
 
   shard_type *shard = &g_shards[GPR_HASH_POINTER(timer, NUM_SHARDS)];
   gpr_mu_lock(&shard->mu);
+  if (grpc_timer_trace) {
+    gpr_log(GPR_DEBUG, "TIMER %p: CANCEL pending=%s", timer,
+            timer->pending ? "true" : "false");
+  }
   if (timer->pending) {
     grpc_closure_sched(exec_ctx, timer->closure, GRPC_ERROR_CANCELLED);
     timer->pending = false;
@@ -260,7 +340,7 @@ void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
    for timers that fall at or under it.  Returns true if the queue is no
    longer empty.
    REQUIRES: shard->mu locked */
-static int refill_queue(shard_type *shard, gpr_timespec now) {
+static int refill_queue(shard_type *shard, gpr_atm now) {
   /* Compute the new queue window width and bound by the limits: */
   double computed_deadline_delta =
       grpc_time_averaged_stats_update_average(&shard->stats) *
@@ -271,12 +351,22 @@ static int refill_queue(shard_type *shard, gpr_timespec now) {
   grpc_timer *timer, *next;
 
   /* Compute the new cap and put all timers under it into the queue: */
-  shard->queue_deadline_cap = gpr_time_add(
-      gpr_time_max(now, shard->queue_deadline_cap), dbl_to_ts(deadline_delta));
+  shard->queue_deadline_cap =
+      saturating_add(GPR_MAX(now, shard->queue_deadline_cap),
+                     (gpr_atm)(deadline_delta * 1000.0));
+
+  if (grpc_timer_check_trace) {
+    gpr_log(GPR_DEBUG, "  .. shard[%d]->queue_deadline_cap --> %" PRIdPTR,
+            (int)(shard - g_shards), shard->queue_deadline_cap);
+  }
   for (timer = shard->list.next; timer != &shard->list; timer = next) {
     next = timer->next;
 
-    if (gpr_time_cmp(timer->deadline, shard->queue_deadline_cap) < 0) {
+    if (timer->deadline < shard->queue_deadline_cap) {
+      if (grpc_timer_check_trace) {
+        gpr_log(GPR_DEBUG, "  .. add timer with deadline %" PRIdPTR " to heap",
+                timer->deadline);
+      }
       list_remove(timer);
       grpc_timer_heap_add(&shard->heap, timer);
     }
@@ -287,15 +377,29 @@ static int refill_queue(shard_type *shard, gpr_timespec now) {
 /* This pops the next non-cancelled timer with deadline <= now from the
    queue, or returns NULL if there isn't one.
    REQUIRES: shard->mu locked */
-static grpc_timer *pop_one(shard_type *shard, gpr_timespec now) {
+static grpc_timer *pop_one(shard_type *shard, gpr_atm now) {
   grpc_timer *timer;
   for (;;) {
+    if (grpc_timer_check_trace) {
+      gpr_log(GPR_DEBUG, "  .. shard[%d]: heap_empty=%s",
+              (int)(shard - g_shards),
+              grpc_timer_heap_is_empty(&shard->heap) ? "true" : "false");
+    }
     if (grpc_timer_heap_is_empty(&shard->heap)) {
-      if (gpr_time_cmp(now, shard->queue_deadline_cap) < 0) return NULL;
+      if (now < shard->queue_deadline_cap) return NULL;
       if (!refill_queue(shard, now)) return NULL;
     }
     timer = grpc_timer_heap_top(&shard->heap);
-    if (gpr_time_cmp(timer->deadline, now) > 0) return NULL;
+    if (grpc_timer_check_trace) {
+      gpr_log(GPR_DEBUG,
+              "  .. check top timer deadline=%" PRIdPTR " now=%" PRIdPTR,
+              timer->deadline, now);
+    }
+    if (timer->deadline > now) return NULL;
+    if (grpc_timer_trace) {
+      gpr_log(GPR_DEBUG, "TIMER %p: FIRE %" PRIdPTR "ms late", timer,
+              now - timer->deadline);
+    }
     timer->pending = false;
     grpc_timer_heap_pop(&shard->heap);
     return timer;
@@ -304,7 +408,7 @@ static grpc_timer *pop_one(shard_type *shard, gpr_timespec now) {
 
 /* REQUIRES: shard->mu unlocked */
 static size_t pop_timers(grpc_exec_ctx *exec_ctx, shard_type *shard,
-                         gpr_timespec now, gpr_timespec *new_min_deadline,
+                         gpr_atm now, gpr_atm *new_min_deadline,
                          grpc_error *error) {
   size_t n = 0;
   grpc_timer *timer;
@@ -318,17 +422,29 @@ static size_t pop_timers(grpc_exec_ctx *exec_ctx, shard_type *shard,
   return n;
 }
 
-static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
-                                   gpr_timespec *next, grpc_error *error) {
+static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_atm now,
+                                   gpr_atm *next, grpc_error *error) {
   size_t n = 0;
 
-  /* TODO(ctiller): verify that there are any timers (atomically) here */
+  gpr_atm min_timer = gpr_atm_no_barrier_load(&g_shared_mutables.min_timer);
+  gpr_tls_set(&g_last_seen_min_timer, min_timer);
+  if (now < min_timer) {
+    if (next != NULL) *next = GPR_MIN(*next, min_timer);
+    return 0;
+  }
 
-  if (gpr_spinlock_trylock(&g_checker_mu)) {
-    gpr_mu_lock(&g_mu);
+  if (gpr_spinlock_trylock(&g_shared_mutables.checker_mu)) {
+    gpr_mu_lock(&g_shared_mutables.mu);
 
-    while (gpr_time_cmp(g_shard_queue[0]->min_deadline, now) < 0) {
-      gpr_timespec new_min_deadline;
+    if (grpc_timer_check_trace) {
+      gpr_log(GPR_DEBUG, "  .. shard[%d]->min_deadline = %" PRIdPTR,
+              (int)(g_shard_queue[0] - g_shards),
+              g_shard_queue[0]->min_deadline);
+    }
+
+    while (g_shard_queue[0]->min_deadline < now ||
+           (now != GPR_ATM_MAX && g_shard_queue[0]->min_deadline == now)) {
+      gpr_atm new_min_deadline;
 
       /* For efficiency, we pop as many available timers as we can from the
          shard.  This may violate perfect timer deadline ordering, but that
@@ -336,6 +452,14 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
       n +=
           pop_timers(exec_ctx, g_shard_queue[0], now, &new_min_deadline, error);
 
+      if (grpc_timer_check_trace) {
+        gpr_log(GPR_DEBUG, "  .. popped --> %" PRIdPTR
+                           ", shard[%d]->min_deadline %" PRIdPTR
+                           " --> %" PRIdPTR ", now=%" PRIdPTR,
+                n, (int)(g_shard_queue[0] - g_shards),
+                g_shard_queue[0]->min_deadline, new_min_deadline, now);
+      }
+
       /* An grpc_timer_init() on the shard could intervene here, adding a new
          timer that is earlier than new_min_deadline.  However,
          grpc_timer_init() will block on the master_lock before it can call
@@ -346,23 +470,24 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
     }
 
     if (next) {
-      *next = gpr_time_min(*next, g_shard_queue[0]->min_deadline);
+      *next = GPR_MIN(*next, g_shard_queue[0]->min_deadline);
     }
 
-    gpr_mu_unlock(&g_mu);
-    gpr_spinlock_unlock(&g_checker_mu);
+    gpr_atm_no_barrier_store(&g_shared_mutables.min_timer,
+                             g_shard_queue[0]->min_deadline);
+    gpr_mu_unlock(&g_shared_mutables.mu);
+    gpr_spinlock_unlock(&g_shared_mutables.checker_mu);
   } else if (next != NULL) {
     /* TODO(ctiller): this forces calling code to do an short poll, and
        then retry the timer check (because this time through the timer list was
        contended).
 
-       We could reduce the cost here dramatically by keeping a count of how many
-       currently active pollers got through the uncontended case above
+       We could reduce the cost here dramatically by keeping a count of how
+       many currently active pollers got through the uncontended case above
        successfully, and waking up other pollers IFF that count drops to zero.
 
        Once that count is in place, this entire else branch could disappear. */
-    *next = gpr_time_min(
-        *next, gpr_time_add(now, gpr_time_from_millis(1, GPR_TIMESPAN)));
+    *next = GPR_MIN(*next, now + 1);
   }
 
   GRPC_ERROR_UNREF(error);
@@ -372,12 +497,71 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
 
 bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
                       gpr_timespec *next) {
+  // prelude
   GPR_ASSERT(now.clock_type == g_clock_type);
-  return run_some_expired_timers(
-      exec_ctx, now, next,
+  gpr_atm now_atm = timespec_to_atm_round_down(now);
+
+  /* fetch from a thread-local first: this avoids contention on a globally
+     mutable cacheline in the common case */
+  gpr_atm min_timer = gpr_tls_get(&g_last_seen_min_timer);
+  if (now_atm < min_timer) {
+    if (next != NULL) {
+      *next =
+          atm_to_timespec(GPR_MIN(timespec_to_atm_round_up(*next), min_timer));
+    }
+    if (grpc_timer_check_trace) {
+      gpr_log(GPR_DEBUG,
+              "TIMER CHECK SKIP: now_atm=%" PRIdPTR " min_timer=%" PRIdPTR,
+              now_atm, min_timer);
+    }
+    return 0;
+  }
+
+  grpc_error *shutdown_error =
       gpr_time_cmp(now, gpr_inf_future(now.clock_type)) != 0
           ? GRPC_ERROR_NONE
-          : GRPC_ERROR_CREATE_FROM_STATIC_STRING("Shutting down timer system"));
+          : GRPC_ERROR_CREATE_FROM_STATIC_STRING("Shutting down timer system");
+
+  // tracing
+  if (grpc_timer_check_trace) {
+    char *next_str;
+    if (next == NULL) {
+      next_str = gpr_strdup("NULL");
+    } else {
+      gpr_asprintf(&next_str, "%" PRId64 ".%09d [%" PRIdPTR "]", next->tv_sec,
+                   next->tv_nsec, timespec_to_atm_round_down(*next));
+    }
+    gpr_log(GPR_DEBUG, "TIMER CHECK BEGIN: now=%" PRId64 ".%09d [%" PRIdPTR
+                       "] next=%s tls_min=%" PRIdPTR " glob_min=%" PRIdPTR,
+            now.tv_sec, now.tv_nsec, now_atm, next_str,
+            gpr_tls_get(&g_last_seen_min_timer),
+            gpr_atm_no_barrier_load(&g_shared_mutables.min_timer));
+    gpr_free(next_str);
+  }
+  // actual code
+  bool r;
+  gpr_atm next_atm;
+  if (next == NULL) {
+    r = run_some_expired_timers(exec_ctx, now_atm, NULL, shutdown_error);
+  } else {
+    next_atm = timespec_to_atm_round_down(*next);
+    r = run_some_expired_timers(exec_ctx, now_atm, &next_atm, shutdown_error);
+    *next = atm_to_timespec(next_atm);
+  }
+  // tracing
+  if (grpc_timer_check_trace) {
+    char *next_str;
+    if (next == NULL) {
+      next_str = gpr_strdup("NULL");
+    } else {
+      gpr_asprintf(&next_str, "%" PRId64 ".%09d [%" PRIdPTR "]", next->tv_sec,
+                   next->tv_nsec, next_atm);
+    }
+    gpr_log(GPR_DEBUG, "TIMER CHECK END: %d timers triggered; next=%s", r,
+            next_str);
+    gpr_free(next_str);
+  }
+  return r > 0;
 }
 
 #endif /* GRPC_TIMER_USE_GENERIC */