aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/core/lib/iomgr/timer.c
blob: 9975fa167153c76a451b419c9d8e187fad083812 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
/*
 *
 * Copyright 2015, 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/lib/iomgr/timer.h"

#include <grpc/support/log.h>
#include <grpc/support/sync.h>
#include <grpc/support/useful.h>
#include "src/core/lib/iomgr/time_averaged_stats.h"
#include "src/core/lib/iomgr/timer_heap.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 bool g_initialized = false;

static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
                                   gpr_timespec *next, grpc_error *error);

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;

  g_initialized = true;
  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,
                          GRPC_ERROR_CREATE("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);
  gpr_mu_destroy(&g_checker_mu);
  g_initialized = false;
}

/* 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;

  if (!g_initialized) {
    timer->triggered = 1;
    grpc_exec_ctx_sched(
        exec_ctx, &timer->closure,
        GRPC_ERROR_CREATE("Attempt to create timer before initialization"),
        NULL);
    return;
  }

  if (gpr_time_cmp(deadline, now) <= 0) {
    timer->triggered = 1;
    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_NONE, NULL);
    return;
  }

  /* 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) {
  if (!g_initialized) {
    /* must have already been cancelled, also the shard mutex is invalid */
    return;
  }

  shard_type *shard = &g_shards[shard_idx(timer)];
  gpr_mu_lock(&shard->mu);
  if (!timer->triggered) {
    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_CANCELLED, 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,
                         grpc_error *error) {
  size_t n = 0;
  grpc_timer *timer;
  gpr_mu_lock(&shard->mu);
  while ((timer = pop_one(shard, now))) {
    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_REF(error), 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, grpc_error *error) {
  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, error);

      /* 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);
  } 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
       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)));
  }

  GRPC_ERROR_UNREF(error);

  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
          ? GRPC_ERROR_NONE
          : GRPC_ERROR_CREATE("Shutting down timer system"));
}