aboutsummaryrefslogtreecommitdiffhomepage
path: root/src/ruby/ext/grpc/rb_channel.c
blob: f0af54d9e58e174307828021dbbcdb21be19c137 (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
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include <ruby/ruby.h>
#include <ruby/thread.h>

#include "rb_byte_buffer.h"
#include "rb_channel.h"
#include "rb_grpc_imports.generated.h"

#include <grpc/grpc.h>
#include <grpc/grpc_security.h>
#include <grpc/support/alloc.h>
#include <grpc/support/log.h>
#include <grpc/support/time.h>
#include "rb_call.h"
#include "rb_channel_args.h"
#include "rb_channel_credentials.h"
#include "rb_completion_queue.h"
#include "rb_grpc.h"
#include "rb_server.h"

/* id_channel is the name of the hidden ivar that preserves a reference to the
 * channel on a call, so that calls are not GCed before their channel.  */
static ID id_channel;

/* id_target is the name of the hidden ivar that preserves a reference to the
 * target string used to create the call, preserved so that it does not get
 * GCed before the channel */
static ID id_target;

/* id_insecure_channel is used to indicate that a channel is insecure */
static VALUE id_insecure_channel;

/* grpc_rb_cChannel is the ruby class that proxies grpc_channel. */
static VALUE grpc_rb_cChannel = Qnil;

/* Used during the conversion of a hash to channel args during channel setup */
static VALUE grpc_rb_cChannelArgs;

typedef struct bg_watched_channel {
  grpc_channel *channel;
  // these fields must only be accessed under global_connection_polling_mu
  struct bg_watched_channel *next;
  int channel_destroyed;
  int refcount;
} bg_watched_channel;

/* grpc_rb_channel wraps a grpc_channel. */
typedef struct grpc_rb_channel {
  VALUE credentials;

  /* The actual channel (protected in a wrapper to tell when it's safe to
   * destroy) */
  bg_watched_channel *bg_wrapped;
} grpc_rb_channel;

typedef enum { CONTINUOUS_WATCH, WATCH_STATE_API } watch_state_op_type;

typedef struct watch_state_op {
  watch_state_op_type op_type;
  // from event.success
  union {
    struct {
      int success;
      // has been called back due to a cq next call
      int called_back;
    } api_callback_args;
    struct {
      bg_watched_channel *bg;
    } continuous_watch_callback_args;
  } op;
} watch_state_op;

static bg_watched_channel *bg_watched_channel_list_head = NULL;

static void grpc_rb_channel_try_register_connection_polling(
    bg_watched_channel *bg);
static void *wait_until_channel_polling_thread_started_no_gil(void *);
static void wait_until_channel_polling_thread_started_unblocking_func(void *);
static void *channel_init_try_register_connection_polling_without_gil(
    void *arg);

typedef struct channel_init_try_register_stack {
  grpc_channel *channel;
  grpc_rb_channel *wrapper;
} channel_init_try_register_stack;

static grpc_completion_queue *channel_polling_cq;
static gpr_mu global_connection_polling_mu;
static gpr_cv global_connection_polling_cv;
static int abort_channel_polling = 0;
static int channel_polling_thread_started = 0;

static int bg_watched_channel_list_lookup(bg_watched_channel *bg);
static bg_watched_channel *bg_watched_channel_list_create_and_add(
    grpc_channel *channel);
static void bg_watched_channel_list_free_and_remove(bg_watched_channel *bg);
static void run_poll_channels_loop_unblocking_func(void *arg);

// Needs to be called under global_connection_polling_mu
static void grpc_rb_channel_watch_connection_state_op_complete(
    watch_state_op *op, int success) {
  GPR_ASSERT(!op->op.api_callback_args.called_back);
  op->op.api_callback_args.called_back = 1;
  op->op.api_callback_args.success = success;
  // wake up the watch API call thats waiting on this op
  gpr_cv_broadcast(&global_connection_polling_cv);
}

/* Avoids destroying a channel twice. */
static void grpc_rb_channel_safe_destroy(bg_watched_channel *bg) {
  gpr_mu_lock(&global_connection_polling_mu);
  GPR_ASSERT(bg_watched_channel_list_lookup(bg));
  if (!bg->channel_destroyed) {
    grpc_channel_destroy(bg->channel);
    bg->channel_destroyed = 1;
  }
  bg->refcount--;
  if (bg->refcount == 0) {
    bg_watched_channel_list_free_and_remove(bg);
  }
  gpr_mu_unlock(&global_connection_polling_mu);
}

static void *channel_safe_destroy_without_gil(void *arg) {
  grpc_rb_channel_safe_destroy((bg_watched_channel *)arg);
  return NULL;
}

/* Destroys Channel instances. */
static void grpc_rb_channel_free(void *p) {
  grpc_rb_channel *ch = NULL;
  if (p == NULL) {
    return;
  };
  ch = (grpc_rb_channel *)p;

  if (ch->bg_wrapped != NULL) {
    /* assumption made here: it's ok to directly gpr_mu_lock the global
     * connection polling mutex becuse we're in a finalizer,
     * and we can count on this thread to not be interrupted or
     * yield the gil. */
    grpc_rb_channel_safe_destroy(ch->bg_wrapped);
    ch->bg_wrapped = NULL;
  }

  xfree(p);
}

/* Protects the mark object from GC */
static void grpc_rb_channel_mark(void *p) {
  grpc_rb_channel *channel = NULL;
  if (p == NULL) {
    return;
  }
  channel = (grpc_rb_channel *)p;
  if (channel->credentials != Qnil) {
    rb_gc_mark(channel->credentials);
  }
}

static rb_data_type_t grpc_channel_data_type = {"grpc_channel",
                                                {grpc_rb_channel_mark,
                                                 grpc_rb_channel_free,
                                                 GRPC_RB_MEMSIZE_UNAVAILABLE,
                                                 {NULL, NULL}},
                                                NULL,
                                                NULL,
#ifdef RUBY_TYPED_FREE_IMMEDIATELY
                                                RUBY_TYPED_FREE_IMMEDIATELY
#endif
};

/* Allocates grpc_rb_channel instances. */
static VALUE grpc_rb_channel_alloc(VALUE cls) {
  grpc_rb_channel *wrapper = ALLOC(grpc_rb_channel);
  wrapper->bg_wrapped = NULL;
  wrapper->credentials = Qnil;
  return TypedData_Wrap_Struct(cls, &grpc_channel_data_type, wrapper);
}

/*
  call-seq:
    insecure_channel = Channel:new("myhost:8080", {'arg1': 'value1'},
                                   :this_channel_is_insecure)
    creds = ...
    secure_channel = Channel:new("myhost:443", {'arg1': 'value1'}, creds)

  Creates channel instances. */
static VALUE grpc_rb_channel_init(int argc, VALUE *argv, VALUE self) {
  VALUE channel_args = Qnil;
  VALUE credentials = Qnil;
  VALUE target = Qnil;
  grpc_rb_channel *wrapper = NULL;
  grpc_channel *ch = NULL;
  grpc_channel_credentials *creds = NULL;
  char *target_chars = NULL;
  grpc_channel_args args;
  channel_init_try_register_stack stack;
  int stop_waiting_for_thread_start = 0;
  MEMZERO(&args, grpc_channel_args, 1);

  grpc_ruby_once_init();
  rb_thread_call_without_gvl(
      wait_until_channel_polling_thread_started_no_gil,
      &stop_waiting_for_thread_start,
      wait_until_channel_polling_thread_started_unblocking_func,
      &stop_waiting_for_thread_start);

  /* "3" == 3 mandatory args */
  rb_scan_args(argc, argv, "3", &target, &channel_args, &credentials);

  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  target_chars = StringValueCStr(target);
  grpc_rb_hash_convert_to_channel_args(channel_args, &args);
  if (TYPE(credentials) == T_SYMBOL) {
    if (id_insecure_channel != SYM2ID(credentials)) {
      rb_raise(rb_eTypeError,
               "bad creds symbol, want :this_channel_is_insecure");
      return Qnil;
    }
    ch = grpc_insecure_channel_create(target_chars, &args, NULL);
  } else {
    wrapper->credentials = credentials;
    creds = grpc_rb_get_wrapped_channel_credentials(credentials);
    ch = grpc_secure_channel_create(creds, target_chars, &args, NULL);
  }

  GPR_ASSERT(ch);
  stack.channel = ch;
  stack.wrapper = wrapper;
  rb_thread_call_without_gvl(
      channel_init_try_register_connection_polling_without_gil, &stack, NULL,
      NULL);

  if (args.args != NULL) {
    xfree(args.args); /* Allocated by grpc_rb_hash_convert_to_channel_args */
  }
  if (ch == NULL) {
    rb_raise(rb_eRuntimeError, "could not create an rpc channel to target:%s",
             target_chars);
    return Qnil;
  }
  rb_ivar_set(self, id_target, target);
  return self;
}

typedef struct get_state_stack {
  bg_watched_channel *bg;
  int try_to_connect;
  int out;
} get_state_stack;

static void *get_state_without_gil(void *arg) {
  get_state_stack *stack = (get_state_stack *)arg;

  gpr_mu_lock(&global_connection_polling_mu);
  GPR_ASSERT(abort_channel_polling || channel_polling_thread_started);
  if (stack->bg->channel_destroyed) {
    stack->out = GRPC_CHANNEL_SHUTDOWN;
  } else {
    stack->out = grpc_channel_check_connectivity_state(stack->bg->channel,
                                                       stack->try_to_connect);
  }
  gpr_mu_unlock(&global_connection_polling_mu);

  return NULL;
}

/*
  call-seq:
    ch.connectivity_state       -> state
    ch.connectivity_state(true) -> state

  Indicates the current state of the channel, whose value is one of the
  constants defined in GRPC::Core::ConnectivityStates.

  It also tries to connect if the chennel is idle in the second form. */
static VALUE grpc_rb_channel_get_connectivity_state(int argc, VALUE *argv,
                                                    VALUE self) {
  VALUE try_to_connect_param = Qfalse;
  grpc_rb_channel *wrapper = NULL;
  get_state_stack stack;

  /* "01" == 0 mandatory args, 1 (try_to_connect) is optional */
  rb_scan_args(argc, argv, "01", &try_to_connect_param);

  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  if (wrapper->bg_wrapped == NULL) {
    rb_raise(rb_eRuntimeError, "closed!");
    return Qnil;
  }

  stack.bg = wrapper->bg_wrapped;
  stack.try_to_connect = RTEST(try_to_connect_param) ? 1 : 0;
  rb_thread_call_without_gvl(get_state_without_gil, &stack, NULL, NULL);

  return LONG2NUM(stack.out);
}

typedef struct watch_state_stack {
  grpc_channel *channel;
  gpr_timespec deadline;
  int last_state;
} watch_state_stack;

static void *wait_for_watch_state_op_complete_without_gvl(void *arg) {
  watch_state_stack *stack = (watch_state_stack *)arg;
  watch_state_op *op = NULL;
  void *success = (void *)0;

  gpr_mu_lock(&global_connection_polling_mu);
  // its unsafe to do a "watch" after "channel polling abort" because the cq has
  // been shut down.
  if (abort_channel_polling) {
    gpr_mu_unlock(&global_connection_polling_mu);
    return (void *)0;
  }
  op = gpr_zalloc(sizeof(watch_state_op));
  op->op_type = WATCH_STATE_API;
  grpc_channel_watch_connectivity_state(stack->channel, stack->last_state,
                                        stack->deadline, channel_polling_cq,
                                        op);

  while (!op->op.api_callback_args.called_back) {
    gpr_cv_wait(&global_connection_polling_cv, &global_connection_polling_mu,
                gpr_inf_future(GPR_CLOCK_REALTIME));
  }
  if (op->op.api_callback_args.success) {
    success = (void *)1;
  }
  gpr_free(op);
  gpr_mu_unlock(&global_connection_polling_mu);

  return success;
}
static void wait_for_watch_state_op_complete_unblocking_func(void *arg) {
  bg_watched_channel *bg = (bg_watched_channel *)arg;
  gpr_mu_lock(&global_connection_polling_mu);
  if (!bg->channel_destroyed) {
    grpc_channel_destroy(bg->channel);
    bg->channel_destroyed = 1;
  }
  gpr_mu_unlock(&global_connection_polling_mu);
}

/* Wait until the channel's connectivity state becomes different from
 * "last_state", or "deadline" expires.
 * Returns true if the the channel's connectivity state becomes
 * different from "last_state" within "deadline".
 * Returns false if "deadline" expires before the channel's connectivity
 * state changes from "last_state".
 * */
static VALUE grpc_rb_channel_watch_connectivity_state(VALUE self,
                                                      VALUE last_state,
                                                      VALUE deadline) {
  grpc_rb_channel *wrapper = NULL;
  watch_state_stack stack;
  void *op_success = 0;

  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);

  if (wrapper->bg_wrapped == NULL) {
    rb_raise(rb_eRuntimeError, "closed!");
    return Qnil;
  }

  if (!FIXNUM_P(last_state)) {
    rb_raise(
        rb_eTypeError,
        "bad type for last_state. want a GRPC::Core::ChannelState constant");
    return Qnil;
  }

  stack.channel = wrapper->bg_wrapped->channel;
  stack.deadline = grpc_rb_time_timeval(deadline, 0),
  stack.last_state = NUM2LONG(last_state);

  op_success = rb_thread_call_without_gvl(
      wait_for_watch_state_op_complete_without_gvl, &stack,
      wait_for_watch_state_op_complete_unblocking_func, wrapper->bg_wrapped);

  return op_success ? Qtrue : Qfalse;
}

/* Create a call given a grpc_channel, in order to call method. The request
   is not sent until grpc_call_invoke is called. */
static VALUE grpc_rb_channel_create_call(VALUE self, VALUE parent, VALUE mask,
                                         VALUE method, VALUE host,
                                         VALUE deadline) {
  VALUE res = Qnil;
  grpc_rb_channel *wrapper = NULL;
  grpc_call *call = NULL;
  grpc_call *parent_call = NULL;
  grpc_completion_queue *cq = NULL;
  int flags = GRPC_PROPAGATE_DEFAULTS;
  grpc_slice method_slice;
  grpc_slice host_slice;
  grpc_slice *host_slice_ptr = NULL;
  char *tmp_str = NULL;

  if (host != Qnil) {
    host_slice =
        grpc_slice_from_copied_buffer(RSTRING_PTR(host), RSTRING_LEN(host));
    host_slice_ptr = &host_slice;
  }
  if (mask != Qnil) {
    flags = NUM2UINT(mask);
  }
  if (parent != Qnil) {
    parent_call = grpc_rb_get_wrapped_call(parent);
  }

  cq = grpc_completion_queue_create_for_pluck(NULL);
  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  if (wrapper->bg_wrapped == NULL) {
    rb_raise(rb_eRuntimeError, "closed!");
    return Qnil;
  }

  method_slice =
      grpc_slice_from_copied_buffer(RSTRING_PTR(method), RSTRING_LEN(method));

  call = grpc_channel_create_call(wrapper->bg_wrapped->channel, parent_call,
                                  flags, cq, method_slice, host_slice_ptr,
                                  grpc_rb_time_timeval(deadline,
                                                       /* absolute time */ 0),
                                  NULL);

  if (call == NULL) {
    tmp_str = grpc_slice_to_c_string(method_slice);
    rb_raise(rb_eRuntimeError, "cannot create call with method %s", tmp_str);
    return Qnil;
  }

  grpc_slice_unref(method_slice);
  if (host_slice_ptr != NULL) {
    grpc_slice_unref(host_slice);
  }

  res = grpc_rb_wrap_call(call, cq);

  /* Make this channel an instance attribute of the call so that it is not GCed
   * before the call. */
  rb_ivar_set(res, id_channel, self);
  return res;
}

/* Closes the channel, calling it's destroy method */
/* Note this is an API-level call; a wrapped channel's finalizer doesn't call
 * this */
static VALUE grpc_rb_channel_destroy(VALUE self) {
  grpc_rb_channel *wrapper = NULL;

  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  if (wrapper->bg_wrapped != NULL) {
    rb_thread_call_without_gvl(channel_safe_destroy_without_gil,
                               wrapper->bg_wrapped, NULL, NULL);
    wrapper->bg_wrapped = NULL;
  }

  return Qnil;
}

/* Called to obtain the target that this channel accesses. */
static VALUE grpc_rb_channel_get_target(VALUE self) {
  grpc_rb_channel *wrapper = NULL;
  VALUE res = Qnil;
  char *target = NULL;

  TypedData_Get_Struct(self, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  target = grpc_channel_get_target(wrapper->bg_wrapped->channel);
  res = rb_str_new2(target);
  gpr_free(target);

  return res;
}

/* Needs to be called under global_connection_polling_mu */
static int bg_watched_channel_list_lookup(bg_watched_channel *target) {
  bg_watched_channel *cur = bg_watched_channel_list_head;

  while (cur != NULL) {
    if (cur == target) {
      return 1;
    }
    cur = cur->next;
  }

  return 0;
}

/* Needs to be called under global_connection_polling_mu */
static bg_watched_channel *bg_watched_channel_list_create_and_add(
    grpc_channel *channel) {
  bg_watched_channel *watched = gpr_zalloc(sizeof(bg_watched_channel));

  watched->channel = channel;
  watched->next = bg_watched_channel_list_head;
  watched->refcount = 1;
  bg_watched_channel_list_head = watched;
  return watched;
}

/* Needs to be called under global_connection_polling_mu */
static void bg_watched_channel_list_free_and_remove(
    bg_watched_channel *target) {
  bg_watched_channel *bg = NULL;

  GPR_ASSERT(bg_watched_channel_list_lookup(target));
  GPR_ASSERT(target->channel_destroyed && target->refcount == 0);
  if (bg_watched_channel_list_head == target) {
    bg_watched_channel_list_head = target->next;
    gpr_free(target);
    return;
  }
  bg = bg_watched_channel_list_head;
  while (bg != NULL && bg->next != NULL) {
    if (bg->next == target) {
      bg->next = bg->next->next;
      gpr_free(target);
      return;
    }
    bg = bg->next;
  }
  GPR_ASSERT(0);
}

/* Initialize a grpc_rb_channel's "protected grpc_channel" and try to push
 * it onto the background thread for constant watches. */
static void *channel_init_try_register_connection_polling_without_gil(
    void *arg) {
  channel_init_try_register_stack *stack =
      (channel_init_try_register_stack *)arg;

  gpr_mu_lock(&global_connection_polling_mu);
  stack->wrapper->bg_wrapped =
      bg_watched_channel_list_create_and_add(stack->channel);
  grpc_rb_channel_try_register_connection_polling(stack->wrapper->bg_wrapped);
  gpr_mu_unlock(&global_connection_polling_mu);
  return NULL;
}

// Needs to be called under global_connection_poolling_mu
static void grpc_rb_channel_try_register_connection_polling(
    bg_watched_channel *bg) {
  grpc_connectivity_state conn_state;
  watch_state_op *op = NULL;

  GPR_ASSERT(channel_polling_thread_started || abort_channel_polling);

  if (bg->refcount == 0) {
    GPR_ASSERT(bg->channel_destroyed);
    bg_watched_channel_list_free_and_remove(bg);
    return;
  }
  GPR_ASSERT(bg->refcount == 1);
  if (bg->channel_destroyed || abort_channel_polling) {
    return;
  }

  conn_state = grpc_channel_check_connectivity_state(bg->channel, 0);
  if (conn_state == GRPC_CHANNEL_SHUTDOWN) {
    return;
  }
  GPR_ASSERT(bg_watched_channel_list_lookup(bg));
  // prevent bg from being free'd by GC while background thread is watching it
  bg->refcount++;

  op = gpr_zalloc(sizeof(watch_state_op));
  op->op_type = CONTINUOUS_WATCH;
  op->op.continuous_watch_callback_args.bg = bg;
  grpc_channel_watch_connectivity_state(bg->channel, conn_state,
                                        gpr_inf_future(GPR_CLOCK_REALTIME),
                                        channel_polling_cq, op);
}

// Note this loop breaks out with a single call of
// "run_poll_channels_loop_no_gil".
// This assumes that a ruby call the unblocking func
// indicates process shutdown.
// In the worst case, this stops polling channel connectivity
// early and falls back to current behavior.
static void *run_poll_channels_loop_no_gil(void *arg) {
  grpc_event event;
  watch_state_op *op = NULL;
  bg_watched_channel *bg = NULL;
  (void)arg;
  gpr_log(GPR_DEBUG, "GRPC_RUBY: run_poll_channels_loop_no_gil - begin");

  gpr_mu_lock(&global_connection_polling_mu);
  GPR_ASSERT(!channel_polling_thread_started);
  channel_polling_thread_started = 1;
  gpr_cv_broadcast(&global_connection_polling_cv);
  gpr_mu_unlock(&global_connection_polling_mu);

  for (;;) {
    event = grpc_completion_queue_next(
        channel_polling_cq, gpr_inf_future(GPR_CLOCK_REALTIME), NULL);
    if (event.type == GRPC_QUEUE_SHUTDOWN) {
      break;
    }
    gpr_mu_lock(&global_connection_polling_mu);
    if (event.type == GRPC_OP_COMPLETE) {
      op = (watch_state_op *)event.tag;
      if (op->op_type == CONTINUOUS_WATCH) {
        bg = (bg_watched_channel *)op->op.continuous_watch_callback_args.bg;
        bg->refcount--;
        grpc_rb_channel_try_register_connection_polling(bg);
        gpr_free(op);
      } else if (op->op_type == WATCH_STATE_API) {
        grpc_rb_channel_watch_connection_state_op_complete(
            (watch_state_op *)event.tag, event.success);
      } else {
        GPR_ASSERT(0);
      }
    }
    gpr_mu_unlock(&global_connection_polling_mu);
  }
  grpc_completion_queue_destroy(channel_polling_cq);
  gpr_log(GPR_DEBUG,
          "GRPC_RUBY: run_poll_channels_loop_no_gil - exit connection polling "
          "loop");
  return NULL;
}

// Notify the channel polling loop to cleanup and shutdown.
static void run_poll_channels_loop_unblocking_func(void *arg) {
  bg_watched_channel *bg = NULL;
  (void)arg;

  gpr_mu_lock(&global_connection_polling_mu);
  gpr_log(GPR_DEBUG,
          "GRPC_RUBY: run_poll_channels_loop_unblocking_func - begin aborting "
          "connection polling");
  // early out after first time through
  if (abort_channel_polling) {
    gpr_mu_unlock(&global_connection_polling_mu);
    return;
  }
  abort_channel_polling = 1;

  // force pending watches to end by switching to shutdown state
  bg = bg_watched_channel_list_head;
  while (bg != NULL) {
    if (!bg->channel_destroyed) {
      grpc_channel_destroy(bg->channel);
      bg->channel_destroyed = 1;
    }
    bg = bg->next;
  }

  grpc_completion_queue_shutdown(channel_polling_cq);
  gpr_cv_broadcast(&global_connection_polling_cv);
  gpr_mu_unlock(&global_connection_polling_mu);
  gpr_log(GPR_DEBUG,
          "GRPC_RUBY: run_poll_channels_loop_unblocking_func - end aborting "
          "connection polling");
}

// Poll channel connectivity states in background thread without the GIL.
static VALUE run_poll_channels_loop(VALUE arg) {
  (void)arg;
  gpr_log(
      GPR_DEBUG,
      "GRPC_RUBY: run_poll_channels_loop - create connection polling thread");
  rb_thread_call_without_gvl(run_poll_channels_loop_no_gil, NULL,
                             run_poll_channels_loop_unblocking_func, NULL);

  return Qnil;
}

static void *wait_until_channel_polling_thread_started_no_gil(void *arg) {
  int *stop_waiting = (int *)arg;
  gpr_log(GPR_DEBUG, "GRPC_RUBY: wait for channel polling thread to start");
  gpr_mu_lock(&global_connection_polling_mu);
  while (!channel_polling_thread_started && !abort_channel_polling &&
         !*stop_waiting) {
    gpr_cv_wait(&global_connection_polling_cv, &global_connection_polling_mu,
                gpr_inf_future(GPR_CLOCK_REALTIME));
  }
  gpr_mu_unlock(&global_connection_polling_mu);

  return NULL;
}

static void wait_until_channel_polling_thread_started_unblocking_func(
    void *arg) {
  int *stop_waiting = (int *)arg;
  gpr_mu_lock(&global_connection_polling_mu);
  gpr_log(GPR_DEBUG,
          "GRPC_RUBY: interrupt wait for channel polling thread to start");
  *stop_waiting = 1;
  gpr_cv_broadcast(&global_connection_polling_cv);
  gpr_mu_unlock(&global_connection_polling_mu);
}

static void *set_abort_channel_polling_without_gil(void *arg) {
  (void)arg;
  gpr_mu_lock(&global_connection_polling_mu);
  abort_channel_polling = 1;
  gpr_cv_broadcast(&global_connection_polling_cv);
  gpr_mu_unlock(&global_connection_polling_mu);
  return NULL;
}

/* Temporary fix for
 * https://github.com/GoogleCloudPlatform/google-cloud-ruby/issues/899.
 * Transports in idle channels can get destroyed. Normally c-core re-connects,
 * but in grpc-ruby core never gets a thread until an RPC is made, because ruby
 * only calls c-core's "completion_queu_pluck" API.
 * This uses a global background thread that calls
 * "completion_queue_next" on registered "watch_channel_connectivity_state"
 * calls - so that c-core can reconnect if needed, when there aren't any RPC's.
 * TODO(apolcyn) remove this when core handles new RPCs on dead connections.
 */
void grpc_rb_channel_polling_thread_start() {
  VALUE background_thread = Qnil;

  GPR_ASSERT(!abort_channel_polling);
  GPR_ASSERT(!channel_polling_thread_started);
  GPR_ASSERT(channel_polling_cq == NULL);

  gpr_mu_init(&global_connection_polling_mu);
  gpr_cv_init(&global_connection_polling_cv);

  channel_polling_cq = grpc_completion_queue_create_for_next(NULL);
  background_thread = rb_thread_create(run_poll_channels_loop, NULL);

  if (!RTEST(background_thread)) {
    gpr_log(GPR_DEBUG, "GRPC_RUBY: failed to spawn channel polling thread");
    rb_thread_call_without_gvl(set_abort_channel_polling_without_gil, NULL,
                               NULL, NULL);
  }
}

static void Init_grpc_propagate_masks() {
  /* Constants representing call propagation masks in grpc.h */
  VALUE grpc_rb_mPropagateMasks =
      rb_define_module_under(grpc_rb_mGrpcCore, "PropagateMasks");
  rb_define_const(grpc_rb_mPropagateMasks, "DEADLINE",
                  UINT2NUM(GRPC_PROPAGATE_DEADLINE));
  rb_define_const(grpc_rb_mPropagateMasks, "CENSUS_STATS_CONTEXT",
                  UINT2NUM(GRPC_PROPAGATE_CENSUS_STATS_CONTEXT));
  rb_define_const(grpc_rb_mPropagateMasks, "CENSUS_TRACING_CONTEXT",
                  UINT2NUM(GRPC_PROPAGATE_CENSUS_TRACING_CONTEXT));
  rb_define_const(grpc_rb_mPropagateMasks, "CANCELLATION",
                  UINT2NUM(GRPC_PROPAGATE_CANCELLATION));
  rb_define_const(grpc_rb_mPropagateMasks, "DEFAULTS",
                  UINT2NUM(GRPC_PROPAGATE_DEFAULTS));
}

static void Init_grpc_connectivity_states() {
  /* Constants representing call propagation masks in grpc.h */
  VALUE grpc_rb_mConnectivityStates =
      rb_define_module_under(grpc_rb_mGrpcCore, "ConnectivityStates");
  rb_define_const(grpc_rb_mConnectivityStates, "IDLE",
                  LONG2NUM(GRPC_CHANNEL_IDLE));
  rb_define_const(grpc_rb_mConnectivityStates, "CONNECTING",
                  LONG2NUM(GRPC_CHANNEL_CONNECTING));
  rb_define_const(grpc_rb_mConnectivityStates, "READY",
                  LONG2NUM(GRPC_CHANNEL_READY));
  rb_define_const(grpc_rb_mConnectivityStates, "TRANSIENT_FAILURE",
                  LONG2NUM(GRPC_CHANNEL_TRANSIENT_FAILURE));
  rb_define_const(grpc_rb_mConnectivityStates, "FATAL_FAILURE",
                  LONG2NUM(GRPC_CHANNEL_SHUTDOWN));
}

void Init_grpc_channel() {
  grpc_rb_cChannelArgs = rb_define_class("TmpChannelArgs", rb_cObject);
  grpc_rb_cChannel =
      rb_define_class_under(grpc_rb_mGrpcCore, "Channel", rb_cObject);

  /* Allocates an object managed by the ruby runtime */
  rb_define_alloc_func(grpc_rb_cChannel, grpc_rb_channel_alloc);

  /* Provides a ruby constructor and support for dup/clone. */
  rb_define_method(grpc_rb_cChannel, "initialize", grpc_rb_channel_init, -1);
  rb_define_method(grpc_rb_cChannel, "initialize_copy",
                   grpc_rb_cannot_init_copy, 1);

  /* Add ruby analogues of the Channel methods. */
  rb_define_method(grpc_rb_cChannel, "connectivity_state",
                   grpc_rb_channel_get_connectivity_state, -1);
  rb_define_method(grpc_rb_cChannel, "watch_connectivity_state",
                   grpc_rb_channel_watch_connectivity_state, 2);
  rb_define_method(grpc_rb_cChannel, "create_call", grpc_rb_channel_create_call,
                   5);
  rb_define_method(grpc_rb_cChannel, "target", grpc_rb_channel_get_target, 0);
  rb_define_method(grpc_rb_cChannel, "destroy", grpc_rb_channel_destroy, 0);
  rb_define_alias(grpc_rb_cChannel, "close", "destroy");

  id_channel = rb_intern("__channel");
  id_target = rb_intern("__target");
  rb_define_const(grpc_rb_cChannel, "SSL_TARGET",
                  ID2SYM(rb_intern(GRPC_SSL_TARGET_NAME_OVERRIDE_ARG)));
  rb_define_const(grpc_rb_cChannel, "ENABLE_CENSUS",
                  ID2SYM(rb_intern(GRPC_ARG_ENABLE_CENSUS)));
  rb_define_const(grpc_rb_cChannel, "MAX_CONCURRENT_STREAMS",
                  ID2SYM(rb_intern(GRPC_ARG_MAX_CONCURRENT_STREAMS)));
  rb_define_const(grpc_rb_cChannel, "MAX_MESSAGE_LENGTH",
                  ID2SYM(rb_intern(GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH)));
  id_insecure_channel = rb_intern("this_channel_is_insecure");
  Init_grpc_propagate_masks();
  Init_grpc_connectivity_states();
}

/* Gets the wrapped channel from the ruby wrapper */
grpc_channel *grpc_rb_get_wrapped_channel(VALUE v) {
  grpc_rb_channel *wrapper = NULL;
  TypedData_Get_Struct(v, grpc_rb_channel, &grpc_channel_data_type, wrapper);
  return wrapper->bg_wrapped->channel;
}