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rails--rails/activesupport/test/share_lock_test.rb

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# frozen_string_literal: true
require "abstract_unit"
require "concurrent/atomic/count_down_latch"
require "active_support/concurrency/share_lock"
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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
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def test_sharing_doesnt_block
with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_latch|
assert_threads_not_stuck(Thread.new { @lock.sharing { } })
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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 { } }
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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 { } }
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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 { }
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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 { }
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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 { }
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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]) { }
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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
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def test_exclusive_conflicting_purpose
[true, false].each do |use_upgrading|
with_thread_waiting_in_lock_section(:sharing) do |sharing_thread_release_latch|
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]) { }
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end
end
]
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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
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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
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end
ensure
conflicting_exclusive_threads.each(&:kill)
no_purpose_thread.kill
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end
end
end
def test_exclusive_ordering
scratch_pad = []
scratch_pad_mutex = Mutex.new
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load_params = [:load, [:load]]
unload_params = [:unload, [:unload, :load]]
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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 }
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end
end
end
end
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sleep(0.01)
scratch_pad_mutex.synchronize { assert_empty scratch_pad }
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sharing_thread_release_latch.count_down
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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
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def test_manual_recursive_yield_cannot_expand_outer_compatible
ready = Concurrent::CyclicBarrier.new(2)
do_compatible_nesting = Concurrent::CountDownLatch.new
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in_compatible_nesting = Concurrent::CountDownLatch.new
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incompatible_thread = Thread.new do
@lock.sharing do
ready.wait
@lock.exclusive(purpose: :x) { }
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end
end
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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
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end
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assert_threads_stuck incompatible_thread
do_compatible_nesting.count_down
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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
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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
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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
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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
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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
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include CustomAssertions
def with_thread_waiting_in_lock_section(lock_section)
in_section = Concurrent::CountDownLatch.new
section_release = Concurrent::CountDownLatch.new
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stuck_thread = Thread.new do
@lock.send(lock_section) do
in_section.count_down
section_release.wait
end
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end
in_section.wait
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yield section_release
ensure
section_release.count_down
stuck_thread.join # clean up
end
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end