Initial checkin of gRPC to third_party/

third_party/grpc/src/core/iomgr/timer.c

+/*
+ *
+ * Copyright 2015-2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/iomgr/timer.h"
+
+#include "src/core/iomgr/timer_heap.h"
+#include "src/core/iomgr/time_averaged_stats.h"
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/useful.h>
+
+#define INVALID_HEAP_INDEX 0xffffffffu
+
+#define LOG2_NUM_SHARDS 5
+#define NUM_SHARDS (1 << LOG2_NUM_SHARDS)
+#define ADD_DEADLINE_SCALE 0.33
+#define MIN_QUEUE_WINDOW_DURATION 0.01
+#define MAX_QUEUE_WINDOW_DURATION 1
+
+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;
+  /* Index in the g_shard_queue */
+  uint32_t shard_queue_index;
+  /* This holds all timers with deadlines < queue_deadline_cap. Timers in this
+     list have the top bit of their deadline set to 0. */
+  grpc_timer_heap heap;
+  /* This holds timers whose deadline is >= queue_deadline_cap. */
+  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_mu g_checker_mu;
+static gpr_clock_type g_clock_type;
+static shard_type g_shards[NUM_SHARDS];
+/* Protected by g_mu */
+static shard_type *g_shard_queue[NUM_SHARDS];
+
+static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
+                                   gpr_timespec *next, int success);
+
+static gpr_timespec compute_min_deadline(shard_type *shard) {
+  return grpc_timer_heap_is_empty(&shard->heap)
+             ? shard->queue_deadline_cap
+             : grpc_timer_heap_top(&shard->heap)->deadline;
+}
+
+void grpc_timer_list_init(gpr_timespec now) {
+  uint32_t i;
+
+  gpr_mu_init(&g_mu);
+  gpr_mu_init(&g_checker_mu);
+  g_clock_type = now.clock_type;
+
+  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->shard_queue_index = i;
+    grpc_timer_heap_init(&shard->heap);
+    shard->list.next = shard->list.prev = &shard->list;
+    shard->min_deadline = compute_min_deadline(shard);
+    g_shard_queue[i] = shard;
+  }
+}
+
+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, 0);
+  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);
+  gpr_mu_destroy(&g_checker_mu);
+}
+
+/* This is a cheap, but good enough, pointer hash for sharding the tasks: */
+static size_t shard_idx(const grpc_timer *info) {
+  size_t x = (size_t)info;
+  return ((x >> 4) ^ (x >> 9) ^ (x >> 14)) & (NUM_SHARDS - 1);
+}
+
+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;
+}
+
+static void list_join(grpc_timer *head, grpc_timer *timer) {
+  timer->next = head;
+  timer->prev = head->prev;
+  timer->next->prev = timer->prev->next = timer;
+}
+
+static void list_remove(grpc_timer *timer) {
+  timer->next->prev = timer->prev;
+  timer->prev->next = timer->next;
+}
+
+static void swap_adjacent_shards_in_queue(uint32_t first_shard_queue_index) {
+  shard_type *temp;
+  temp = g_shard_queue[first_shard_queue_index];
+  g_shard_queue[first_shard_queue_index] =
+      g_shard_queue[first_shard_queue_index + 1];
+  g_shard_queue[first_shard_queue_index + 1] = temp;
+  g_shard_queue[first_shard_queue_index]->shard_queue_index =
+      first_shard_queue_index;
+  g_shard_queue[first_shard_queue_index + 1]->shard_queue_index =
+      first_shard_queue_index + 1;
+}
+
+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) {
+    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) {
+    swap_adjacent_shards_in_queue(shard->shard_queue_index);
+  }
+}
+
+void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
+                     gpr_timespec deadline, grpc_iomgr_cb_func timer_cb,
+                     void *timer_cb_arg, gpr_timespec now) {
+  int is_first_timer = 0;
+  shard_type *shard = &g_shards[shard_idx(timer)];
+  GPR_ASSERT(deadline.clock_type == g_clock_type);
+  GPR_ASSERT(now.clock_type == g_clock_type);
+  grpc_closure_init(&timer->closure, timer_cb, timer_cb_arg);
+  timer->deadline = deadline;
+  timer->triggered = 0;
+
+  /* TODO(ctiller): check deadline expired */
+
+  gpr_mu_lock(&shard->mu);
+  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) {
+    is_first_timer = grpc_timer_heap_add(&shard->heap, timer);
+  } else {
+    timer->heap_index = INVALID_HEAP_INDEX;
+    list_join(&shard->list, timer);
+  }
+  gpr_mu_unlock(&shard->mu);
+
+  /* Deadline may have decreased, we need to adjust the master queue.  Note
+     that there is a potential racy unlocked region here.  There could be a
+     reordering of multiple grpc_timer_init calls, at this point, but the < test
+     below should ensure that we err on the side of caution.  There could
+     also be a race with grpc_timer_check, which might beat us to the lock.  In
+     that case, it is possible that the timer that we added will have already
+     run by the time we hold the lock, but that too is a safe error.
+     Finally, it's possible that the grpc_timer_check that intervened failed to
+     trigger the new timer because the min_deadline hadn't yet been reduced.
+     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;
+      note_deadline_change(shard);
+      if (shard->shard_queue_index == 0 &&
+          gpr_time_cmp(deadline, old_min_deadline) < 0) {
+        grpc_kick_poller();
+      }
+    }
+    gpr_mu_unlock(&g_mu);
+  }
+}
+
+void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
+  shard_type *shard = &g_shards[shard_idx(timer)];
+  gpr_mu_lock(&shard->mu);
+  if (!timer->triggered) {
+    grpc_exec_ctx_enqueue(exec_ctx, &timer->closure, false, NULL);
+    timer->triggered = 1;
+    if (timer->heap_index == INVALID_HEAP_INDEX) {
+      list_remove(timer);
+    } else {
+      grpc_timer_heap_remove(&shard->heap, timer);
+    }
+  }
+  gpr_mu_unlock(&shard->mu);
+}
+
+/* This is called when the queue is empty and "now" has reached the
+   queue_deadline_cap.  We compute a new queue deadline and then scan the map
+   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) {
+  /* Compute the new queue window width and bound by the limits: */
+  double computed_deadline_delta =
+      grpc_time_averaged_stats_update_average(&shard->stats) *
+      ADD_DEADLINE_SCALE;
+  double deadline_delta =
+      GPR_CLAMP(computed_deadline_delta, MIN_QUEUE_WINDOW_DURATION,
+                MAX_QUEUE_WINDOW_DURATION);
+  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));
+  for (timer = shard->list.next; timer != &shard->list; timer = next) {
+    next = timer->next;
+
+    if (gpr_time_cmp(timer->deadline, shard->queue_deadline_cap) < 0) {
+      list_remove(timer);
+      grpc_timer_heap_add(&shard->heap, timer);
+    }
+  }
+  return !grpc_timer_heap_is_empty(&shard->heap);
+}
+
+/* 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) {
+  grpc_timer *timer;
+  for (;;) {
+    if (grpc_timer_heap_is_empty(&shard->heap)) {
+      if (gpr_time_cmp(now, shard->queue_deadline_cap) < 0) 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;
+    timer->triggered = 1;
+    grpc_timer_heap_pop(&shard->heap);
+    return timer;
+  }
+}
+
+/* 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,
+                         int success) {
+  size_t n = 0;
+  grpc_timer *timer;
+  gpr_mu_lock(&shard->mu);
+  while ((timer = pop_one(shard, now))) {
+    grpc_exec_ctx_enqueue(exec_ctx, &timer->closure, success, NULL);
+    n++;
+  }
+  *new_min_deadline = compute_min_deadline(shard);
+  gpr_mu_unlock(&shard->mu);
+  return n;
+}
+
+static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
+                                   gpr_timespec *next, int success) {
+  size_t n = 0;
+
+  /* TODO(ctiller): verify that there are any timers (atomically) here */
+
+  if (gpr_mu_trylock(&g_checker_mu)) {
+    gpr_mu_lock(&g_mu);
+
+    while (gpr_time_cmp(g_shard_queue[0]->min_deadline, now) < 0) {
+      gpr_timespec 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
+         shouldn't be a big deal because we don't make ordering guarantees. */
+      n += pop_timers(exec_ctx, g_shard_queue[0], now, &new_min_deadline,
+                      success);
+
+      /* 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
+         set_min_deadline, so this one will complete first and then the Addtimer
+         will reduce the min_deadline (perhaps unnecessarily). */
+      g_shard_queue[0]->min_deadline = new_min_deadline;
+      note_deadline_change(g_shard_queue[0]);
+    }
+
+    if (next) {
+      *next = gpr_time_min(*next, g_shard_queue[0]->min_deadline);
+    }
+
+    gpr_mu_unlock(&g_mu);
+    gpr_mu_unlock(&g_checker_mu);
+  }
+
+  return (int)n;
+}
+
+bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
+                      gpr_timespec *next) {
+  GPR_ASSERT(now.clock_type == g_clock_type);
+  return run_some_expired_timers(
+      exec_ctx, now, next,
+      gpr_time_cmp(now, gpr_inf_future(now.clock_type)) != 0);
+}