diff options
Diffstat (limited to 'activesupport')
| -rw-r--r-- | activesupport/lib/active_support/concurrency/share_lock.rb | 60 | ||||
| -rw-r--r-- | activesupport/lib/active_support/dependencies.rb | 9 | ||||
| -rw-r--r-- | activesupport/lib/active_support/dependencies/interlock.rb | 16 | ||||
| -rw-r--r-- | activesupport/test/share_lock_test.rb | 333 |
4 files changed, 384 insertions, 34 deletions
diff --git a/activesupport/lib/active_support/concurrency/share_lock.rb b/activesupport/lib/active_support/concurrency/share_lock.rb index f1c6230084..ca48164c54 100644 --- a/activesupport/lib/active_support/concurrency/share_lock.rb +++ b/activesupport/lib/active_support/concurrency/share_lock.rb @@ -9,7 +9,7 @@ module ActiveSupport #-- # Note that a pending Exclusive lock attempt does not block incoming # Share requests (i.e., we are "read-preferring"). That seems - # consistent with the behavior of +loose_upgrades+, but may be the + # consistent with the behavior of "loose" upgrades, but may be the # wrong choice otherwise: it nominally reduces the possibility of # deadlock by risking starvation instead. class ShareLock @@ -20,47 +20,48 @@ module ActiveSupport # to upgrade share locks to exclusive. - # If +loose_upgrades+ is false (the default), then a thread that - # is waiting on an Exclusive lock will continue to hold any Share - # lock that it has already established. This is safer, but can - # lead to deadlock. - # - # If +loose_upgrades+ is true, a thread waiting on an Exclusive - # lock will temporarily relinquish its Share lock. Being less - # strict, this behavior prevents some classes of deadlocks. For - # many resources, loose upgrades are sufficient: if a thread is - # awaiting a lock, it is not running any other code. - attr_reader :loose_upgrades - - def initialize(loose_upgrades = false) - @loose_upgrades = loose_upgrades - + def initialize super() @cv = new_cond @sharing = Hash.new(0) + @waiting = {} @exclusive_thread = nil @exclusive_depth = 0 end - # Returns false if +no_wait+ is specified and the lock is not + # Returns false if +no_wait+ is set and the lock is not # immediately available. Otherwise, returns true after the lock # has been acquired. - def start_exclusive(no_wait=false) + # + # +purpose+ and +compatible+ work together; while this thread is + # waiting for the exclusive lock, it will yield its share (if any) + # to any other attempt whose +purpose+ appears in this attempt's + # +compatible+ list. This allows a "loose" upgrade, which, being + # less strict, prevents some classes of deadlocks. + # + # For many resources, loose upgrades are sufficient: if a thread + # is awaiting a lock, it is not running any other code. With + # +purpose+ matching, it is possible to yield only to other + # threads whose activity will not interfere. + def start_exclusive(purpose: nil, compatible: [], no_wait: false) synchronize do unless @exclusive_thread == Thread.current - return false if no_wait && busy? + if busy?(purpose) + return false if no_wait - loose_shares = nil - if @loose_upgrades loose_shares = @sharing.delete(Thread.current) + @waiting[Thread.current] = compatible if loose_shares + + begin + @cv.wait_while { busy?(purpose) } + ensure + @waiting.delete Thread.current + @sharing[Thread.current] = loose_shares if loose_shares + end end - - @cv.wait_while { busy? } if busy? - @exclusive_thread = Thread.current - @sharing[Thread.current] = loose_shares if loose_shares end @exclusive_depth += 1 @@ -106,8 +107,10 @@ module ActiveSupport # +no_wait+ is set and the lock is not immediately available, # returns +nil+ without yielding. Otherwise, returns the result of # the block. - def exclusive(no_wait=false) - if start_exclusive(no_wait) + # + # See +start_exclusive+ for other options. + def exclusive(purpose: nil, compatible: [], no_wait: false) + if start_exclusive(purpose: purpose, compatible: compatible, no_wait: no_wait) begin yield ensure @@ -129,8 +132,9 @@ module ActiveSupport private # Must be called within synchronize - def busy? + def busy?(purpose) (@exclusive_thread && @exclusive_thread != Thread.current) || + @waiting.any? { |k, v| k != Thread.current && !v.include?(purpose) } || @sharing.size > (@sharing[Thread.current] > 0 ? 1 : 0) end end diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb index be03f65e6e..f76ef04f49 100644 --- a/activesupport/lib/active_support/dependencies.rb +++ b/activesupport/lib/active_support/dependencies.rb @@ -37,6 +37,13 @@ module ActiveSupport #:nodoc: Dependencies.interlock.loading { yield } end + # Execute the supplied block while holding an exclusive lock, + # preventing any other thread from being inside a #run_interlock + # block at the same time + def self.unload_interlock + Dependencies.interlock.unloading { yield } + end + # :nodoc: # Should we turn on Ruby warnings on the first load of dependent files? @@ -346,7 +353,7 @@ module ActiveSupport #:nodoc: def clear log_call - Dependencies.load_interlock do + Dependencies.unload_interlock do loaded.clear loading.clear remove_unloadable_constants! diff --git a/activesupport/lib/active_support/dependencies/interlock.rb b/activesupport/lib/active_support/dependencies/interlock.rb index 148212c951..fbeb904684 100644 --- a/activesupport/lib/active_support/dependencies/interlock.rb +++ b/activesupport/lib/active_support/dependencies/interlock.rb @@ -4,21 +4,27 @@ module ActiveSupport #:nodoc: module Dependencies #:nodoc: class Interlock def initialize # :nodoc: - @lock = ActiveSupport::Concurrency::ShareLock.new(true) + @lock = ActiveSupport::Concurrency::ShareLock.new end def loading - @lock.exclusive do + @lock.exclusive(purpose: :load, compatible: [:load]) do yield end end - # Attempt to obtain a "loading" (exclusive) lock. If possible, + def unloading + @lock.exclusive(purpose: :unload, compatible: [:load, :unload]) do + yield + end + end + + # Attempt to obtain an "unloading" (exclusive) lock. If possible, # execute the supplied block while holding the lock. If there is # concurrent activity, return immediately (without executing the # block) instead of waiting. - def attempt_loading - @lock.exclusive(true) do + def attempt_unloading + @lock.exclusive(purpose: :unload, compatible: [:load, :unload], no_wait: true) do yield end end diff --git a/activesupport/test/share_lock_test.rb b/activesupport/test/share_lock_test.rb new file mode 100644 index 0000000000..ad41db608b --- /dev/null +++ b/activesupport/test/share_lock_test.rb @@ -0,0 +1,333 @@ +require 'abstract_unit' +require 'concurrent/atomics' +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 + conflicting_exclusive_threads = [ + Thread.new do + @lock.send(use_upgrading ? :sharing : :tap) do + @lock.exclusive(purpose: :red, compatible: [:green, :purple]) {} + end + end, + Thread.new do + @lock.send(use_upgrading ? :sharing : :tap) do + @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]] + + [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 + @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_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 |