aboutsummaryrefslogtreecommitdiffstats
path: root/activesupport/test/share_lock_test.rb
blob: a5970591fad980ef8654d47b37cb44691689a483 (plain) (blame)
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
require "abstract_unit"
require "concurrent/atomic/count_down_latch"
require "active_support/concurrency/share_lock"

class ShareLockTest < ActiveSupport::TestCase
  def setup
    @lock = ActiveSupport::Concurrency::ShareLock.new
  end

  def test_reentrancy
    thread = Thread.new do
      @lock.sharing   { @lock.sharing   {} }
      @lock.exclusive { @lock.exclusive {} }
    end
    assert_threads_not_stuck thread
  end

  def test_sharing_doesnt_block
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_latch|
      assert_threads_not_stuck(Thread.new { @lock.sharing {} })
    end
  end

  def test_sharing_blocks_exclusive
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      @lock.exclusive(no_wait: true) { flunk } # polling should fail
      exclusive_thread = Thread.new { @lock.exclusive {} }
      assert_threads_stuck_but_releasable_by_latch exclusive_thread, sharing_thread_release_latch
    end
  end

  def test_exclusive_blocks_sharing
    with_thread_waiting_in_lock_section(:exclusive) do |exclusive_thread_release_latch|
      sharing_thread = Thread.new { @lock.sharing {} }
      assert_threads_stuck_but_releasable_by_latch sharing_thread, exclusive_thread_release_latch
    end
  end

  def test_multiple_exlusives_are_able_to_progress
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      exclusive_threads = (1..2).map do
        Thread.new do
          @lock.exclusive {}
        end
      end

      assert_threads_stuck_but_releasable_by_latch exclusive_threads, sharing_thread_release_latch
    end
  end

  def test_sharing_is_upgradeable_to_exclusive
    upgrading_thread = Thread.new do
      @lock.sharing do
        @lock.exclusive {}
      end
    end
    assert_threads_not_stuck upgrading_thread
  end

  def test_exclusive_upgrade_waits_for_other_sharers_to_leave
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      in_sharing = Concurrent::CountDownLatch.new

      upgrading_thread = Thread.new do
        @lock.sharing do
          in_sharing.count_down
          @lock.exclusive {}
        end
      end

      in_sharing.wait
      assert_threads_stuck_but_releasable_by_latch upgrading_thread, sharing_thread_release_latch
    end
  end

  def test_exclusive_matching_purpose
    [true, false].each do |use_upgrading|
      with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
        exclusive_threads = (1..2).map do
          Thread.new do
            @lock.send(use_upgrading ? :sharing : :tap) do
              @lock.exclusive(purpose: :load, compatible: [:load, :unload]) {}
            end
          end
        end

        assert_threads_stuck_but_releasable_by_latch exclusive_threads, sharing_thread_release_latch
      end
    end
  end

  def test_killed_thread_loses_lock
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      thread = Thread.new do
        @lock.sharing do
          @lock.exclusive {}
        end
      end

      assert_threads_stuck thread
      thread.kill

      sharing_thread_release_latch.count_down

      thread = Thread.new do
        @lock.exclusive {}
      end

      assert_threads_not_stuck thread
    end
  end

  def test_exclusive_conflicting_purpose
    [true, false].each do |use_upgrading|
      with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
        begin
          together = Concurrent::CyclicBarrier.new(2)
          conflicting_exclusive_threads = [
            Thread.new do
              @lock.send(use_upgrading ? :sharing : :tap) do
                together.wait
                @lock.exclusive(purpose: :red, compatible: [:green, :purple]) {}
              end
            end,
            Thread.new do
              @lock.send(use_upgrading ? :sharing : :tap) do
                together.wait
                @lock.exclusive(purpose: :blue, compatible: [:green]) {}
              end
            end
          ]

          assert_threads_stuck conflicting_exclusive_threads # wait for threads to get into their respective `exclusive {}` blocks

          # This thread will be stuck as long as any other thread is in
          # a sharing block. While it's blocked, it holds no lock, so it
          # doesn't interfere with any other attempts.
          no_purpose_thread = Thread.new do
            @lock.exclusive {}
          end
          assert_threads_stuck no_purpose_thread

          # This thread is compatible with both of the "primary"
          # attempts above. It's initially stuck on the outer share
          # lock, but as soon as that's released, it can run --
          # regardless of whether those threads hold share locks.
          compatible_thread = Thread.new do
            @lock.exclusive(purpose: :green, compatible: []) {}
          end
          assert_threads_stuck compatible_thread

          assert_threads_stuck conflicting_exclusive_threads

          sharing_thread_release_latch.count_down

          assert_threads_not_stuck compatible_thread # compatible thread is now able to squeak through

          if use_upgrading
            # The "primary" threads both each hold a share lock, and are
            # mutually incompatible; they're still stuck.
            assert_threads_stuck conflicting_exclusive_threads

            # The thread without a specified purpose is also stuck; it's
            # not compatible with anything.
            assert_threads_stuck no_purpose_thread
          else
            # As the primaries didn't hold a share lock, as soon as the
            # outer one was released, all the exclusive locks are free
            # to be acquired in turn.

            assert_threads_not_stuck conflicting_exclusive_threads
            assert_threads_not_stuck no_purpose_thread
          end
        ensure
          conflicting_exclusive_threads.each(&:kill)
          no_purpose_thread.kill
        end
      end
    end
  end

  def test_exclusive_ordering
    scratch_pad       = []
    scratch_pad_mutex = Mutex.new

    load_params   = [:load,   [:load]]
    unload_params = [:unload, [:unload, :load]]

    all_sharing = Concurrent::CyclicBarrier.new(4)

    [load_params, load_params, unload_params, unload_params].permutation do |thread_params|
      with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
        threads = thread_params.map do |purpose, compatible|
          Thread.new do
            @lock.sharing do
              all_sharing.wait
              @lock.exclusive(purpose: purpose, compatible: compatible) do
                scratch_pad_mutex.synchronize { scratch_pad << purpose }
              end
            end
          end
        end

        sleep(0.01)
        scratch_pad_mutex.synchronize { assert_empty scratch_pad }

        sharing_thread_release_latch.count_down

        assert_threads_not_stuck threads
        scratch_pad_mutex.synchronize do
          assert_equal [:load, :load, :unload, :unload], scratch_pad
          scratch_pad.clear
        end
      end
    end
  end

  def test_new_share_attempts_block_on_waiting_exclusive
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      release_exclusive = Concurrent::CountDownLatch.new

      waiting_exclusive = Thread.new do
        @lock.sharing do
          @lock.exclusive do
            release_exclusive.wait
          end
        end
      end
      assert_threads_stuck waiting_exclusive

      late_share_attempt = Thread.new do
        @lock.sharing {}
      end
      assert_threads_stuck late_share_attempt

      sharing_thread_release_latch.count_down
      assert_threads_stuck late_share_attempt

      release_exclusive.count_down
      assert_threads_not_stuck late_share_attempt
    end
  end

  def test_share_remains_reentrant_ignoring_a_waiting_exclusive
    with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
      ready = Concurrent::CyclicBarrier.new(2)
      attempt_reentrancy = Concurrent::CountDownLatch.new

      sharer = Thread.new do
        @lock.sharing do
          ready.wait
          attempt_reentrancy.wait
          @lock.sharing {}
        end
      end

      exclusive = Thread.new do
        @lock.sharing do
          ready.wait
          @lock.exclusive {}
        end
      end

      assert_threads_stuck exclusive

      attempt_reentrancy.count_down

      assert_threads_not_stuck sharer
      assert_threads_stuck exclusive
    end
  end

  def test_compatible_exclusives_cooperate_to_both_proceed
    ready = Concurrent::CyclicBarrier.new(2)
    done = Concurrent::CyclicBarrier.new(2)

    threads = 2.times.map do
      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.exclusive(purpose: :x, compatible: [:x], after_compatible: [:x]) {}
          done.wait
        end
      end
    end

    assert_threads_not_stuck threads
  end

  def test_manual_yield
    ready = Concurrent::CyclicBarrier.new(2)
    done = Concurrent::CyclicBarrier.new(2)

    threads = [
      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.exclusive(purpose: :x) {}
          done.wait
        end
      end,

      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.yield_shares(compatible: [:x]) do
            done.wait
          end
        end
      end,
    ]

    assert_threads_not_stuck threads
  end

  def test_manual_incompatible_yield
    ready = Concurrent::CyclicBarrier.new(2)
    done = Concurrent::CyclicBarrier.new(2)

    threads = [
      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.exclusive(purpose: :x) {}
          done.wait
        end
      end,

      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.yield_shares(compatible: [:y]) do
            done.wait
          end
        end
      end,
    ]

    assert_threads_stuck threads
  ensure
    threads.each(&:kill) if threads
  end

  def test_manual_recursive_yield
    ready = Concurrent::CyclicBarrier.new(2)
    done = Concurrent::CyclicBarrier.new(2)
    do_nesting = Concurrent::CountDownLatch.new

    threads = [
      Thread.new do
        @lock.sharing do
          ready.wait
          @lock.exclusive(purpose: :x) {}
          done.wait
        end
      end,

      Thread.new do
        @lock.sharing do
          @lock.yield_shares(compatible: [:x]) do
            @lock.sharing do
              ready.wait
              do_nesting.wait
              @lock.yield_shares(compatible: [:x, :y]) do
                done.wait
              end
            end
          end
        end
      end
    ]

    assert_threads_stuck threads
    do_nesting.count_down

    assert_threads_not_stuck threads
  end

  def test_manual_recursive_yield_cannot_expand_outer_compatible
    ready = Concurrent::CyclicBarrier.new(2)
    do_compatible_nesting = Concurrent::CountDownLatch.new
    in_compatible_nesting = Concurrent::CountDownLatch.new

    incompatible_thread = Thread.new do
      @lock.sharing do
        ready.wait
        @lock.exclusive(purpose: :x) {}
      end
    end

    yield_shares_thread = Thread.new do
      @lock.sharing do
        ready.wait
        @lock.yield_shares(compatible: [:y]) do
          do_compatible_nesting.wait
          @lock.sharing do
            @lock.yield_shares(compatible: [:x, :y]) do
              in_compatible_nesting.wait
            end
          end
        end
      end
    end

    assert_threads_stuck incompatible_thread
    do_compatible_nesting.count_down
    assert_threads_stuck incompatible_thread
    in_compatible_nesting.count_down
    assert_threads_not_stuck [yield_shares_thread, incompatible_thread]
  end

  def test_manual_recursive_yield_restores_previous_compatible
    ready = Concurrent::CyclicBarrier.new(2)
    do_nesting = Concurrent::CountDownLatch.new
    after_nesting = Concurrent::CountDownLatch.new

    incompatible_thread = Thread.new do
      ready.wait
      @lock.exclusive(purpose: :z) {}
    end

    recursive_yield_shares_thread = Thread.new do
      @lock.sharing do
        ready.wait
        @lock.yield_shares(compatible: [:y]) do
          do_nesting.wait
          @lock.sharing do
            @lock.yield_shares(compatible: [:x, :y]) {}
          end
          after_nesting.wait
        end
      end
    end

    assert_threads_stuck incompatible_thread
    do_nesting.count_down
    assert_threads_stuck incompatible_thread

    compatible_thread = Thread.new do
      @lock.exclusive(purpose: :y) {}
    end
    assert_threads_not_stuck compatible_thread

    post_nesting_incompatible_thread = Thread.new do
      @lock.exclusive(purpose: :x) {}
    end
    assert_threads_stuck post_nesting_incompatible_thread

    after_nesting.count_down
    assert_threads_not_stuck recursive_yield_shares_thread
    # post_nesting_incompatible_thread can now proceed
    assert_threads_not_stuck post_nesting_incompatible_thread
    # assert_threads_not_stuck can now proceed
    assert_threads_not_stuck incompatible_thread
  end

  def test_in_shared_section_incompatible_non_upgrading_threads_cannot_preempt_upgrading_threads
    scratch_pad       = []
    scratch_pad_mutex = Mutex.new

    upgrading_load_params       = [:load,   [:load],          true]
    non_upgrading_unload_params = [:unload, [:load, :unload], false]

    [upgrading_load_params, non_upgrading_unload_params].permutation do |thread_params|
      with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
        threads = thread_params.map do |purpose, compatible, use_upgrading|
          Thread.new do
            @lock.send(use_upgrading ? :sharing : :tap) do
              @lock.exclusive(purpose: purpose, compatible: compatible) do
                scratch_pad_mutex.synchronize { scratch_pad << purpose }
              end
            end
          end
        end

        assert_threads_stuck threads
        scratch_pad_mutex.synchronize { assert_empty scratch_pad }

        sharing_thread_release_latch.count_down

        assert_threads_not_stuck threads
        scratch_pad_mutex.synchronize do
          assert_equal [:load, :unload], scratch_pad
          scratch_pad.clear
        end
      end
    end
  end

  private

    module CustomAssertions
      SUFFICIENT_TIMEOUT = 0.2

      private

        def assert_threads_stuck_but_releasable_by_latch(threads, latch)
          assert_threads_stuck threads
          latch.count_down
          assert_threads_not_stuck threads
        end

        def assert_threads_stuck(threads)
          sleep(SUFFICIENT_TIMEOUT) # give threads time to do their business
          assert(Array(threads).all? { |t| t.join(0.001).nil? })
        end

        def assert_threads_not_stuck(threads)
          assert(Array(threads).all? { |t| t.join(SUFFICIENT_TIMEOUT) })
        end
    end

    class CustomAssertionsTest < ActiveSupport::TestCase
      include CustomAssertions

      def setup
        @latch = Concurrent::CountDownLatch.new
        @thread = Thread.new { @latch.wait }
      end

      def teardown
        @latch.count_down
        @thread.join
      end

      def test_happy_path
        assert_threads_stuck_but_releasable_by_latch @thread, @latch
      end

      def test_detects_stuck_thread
        assert_raises(Minitest::Assertion) do
          assert_threads_not_stuck @thread
        end
      end

      def test_detects_free_thread
        @latch.count_down
        assert_raises(Minitest::Assertion) do
          assert_threads_stuck @thread
        end
      end

      def test_detects_already_released
        @latch.count_down
        assert_raises(Minitest::Assertion) do
          assert_threads_stuck_but_releasable_by_latch @thread, @latch
        end
      end

      def test_detects_remains_latched
        another_latch = Concurrent::CountDownLatch.new
        assert_raises(Minitest::Assertion) do
          assert_threads_stuck_but_releasable_by_latch @thread, another_latch
        end
      end
    end

    include CustomAssertions

    def with_thread_waiting_in_lock_section(lock_section)
      in_section      = Concurrent::CountDownLatch.new
      section_release = Concurrent::CountDownLatch.new

      stuck_thread = Thread.new do
        @lock.send(lock_section) do
          in_section.count_down
          section_release.wait
        end
      end

      in_section.wait

      yield section_release
    ensure
      section_release.count_down
      stuck_thread.join # clean up
    end
end