Class: ThreadWeaver::IterativeRaceDetector

Inherits:
Object
  • Object
show all
Extended by:
T::Sig
Defined in:
lib/thread_weaver/iterative_race_detector.rb

Instance Method Summary collapse

Constructor Details

#initialize(setup:, run:, check:, target_classes:, assume_deadlocked_after_ms:, run_secondary: nil, expect_nonblocking: false) ⇒ IterativeRaceDetector

Returns a new instance of IterativeRaceDetector.



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# File 'lib/thread_weaver/iterative_race_detector.rb', line 30

def initialize(setup:, run:, check:, target_classes:, assume_deadlocked_after_ms:, run_secondary: nil, expect_nonblocking: false)
  @setup_blk = T.let(setup, T.proc.returns(T.untyped))
  @check_blk = T.let(check, T.proc.params(arg0: T.untyped).returns(T::Boolean))
  @target_classes = T.let(target_classes, T::Array[Module])
  @expect_nonblocking = T.let(expect_nonblocking, T::Boolean)

  @run_blk = T.let(run, T.proc.params(arg0: T.untyped).void)
  # Secondary is optional as the common case will be testing two identical blocks of code
  @run_secondary_blk = T.let(run_secondary || run, T.proc.params(arg0: T.untyped).void)

  @assume_deadlocked_after = T.let(assume_deadlocked_after_ms / 1000.0, Float)

  @scenarios_run = T.let(0, Integer)
  @secondary_deadlocked_count = T.let(0, Integer)
end

Instance Method Details

#check_if_can_run_standalone(blk, name) ⇒ Object 



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# File 'lib/thread_weaver/iterative_race_detector.rb', line 143

def check_if_can_run_standalone(blk, name)
  context = @setup_blk.call
  thread = ControllableThread.new(context, name: name, &blk)
  thread.set_next_instruction(ContinueToThreadEnd.new)

  if check_for_deadlock(thread)
    thread.kill
    message = "#{name} appears to be deadlocked when running alone, with no other concurrent "\
              "threads. #{DEADLOCK_MIGHT_BE_CONFIG}"

    raise DeadlockDetectedError.new(message)
  end

  check_passed = @check_blk.call(context)

  unless check_passed
    message = "#{name} failed check when running alone, with no other concurrent threads. "\
              "Your check logic may be flawed."
    raise RaceConditionDetectedError.new(message)
  end
end

#run ⇒ Object 



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# File 'lib/thread_weaver/iterative_race_detector.rb', line 47

def run
  check_if_can_run_standalone(@run_blk, "run")
  if @run_secondary_blk != @run_blk
    check_if_can_run_standalone(@run_secondary_blk, "run_secondary")
  end

  hold_primary_at_line_count = -1
  done = T.let(false, T::Boolean)

  error_encountered = T.let(nil, T.nilable(Exception))

  until done
    Timeout.timeout(2 * @assume_deadlocked_after) do
      hold_primary_at_line_count += 1

      context = @setup_blk.call

      primary_thread = ControllableThread.new(context, name: "primary_thread", &@run_blk)

      # Pause the primary thread after it executes hold_primary_at_line_count number of lines
      primary_thread.set_and_wait_for_next_instruction(
        PauseWhenLineCount.new(
          count: hold_primary_at_line_count,
          target_classes: @target_classes
        )
      )

      # Start secondary thread and instruct it to run until completion. The primary thread is
      # still paused part-way through its execution
      secondary_thread = ControllableThread.new(context, name: "secondary_thread", &@run_secondary_blk)
      secondary_thread.set_next_instruction(ContinueToThreadEnd.new)

      if check_for_deadlock(secondary_thread)
        # At this point, it appears that the secondary thread is deadlocked. This could be
        # because of a true deadlock, but this also is expected to happen even in thread-safe
        # code that uses blocking locks. If blocking locks are used then its quite likely that
        # pausing the primary thread at certain points might would block the secondary thread.
        # For that reason, this isn't considered an outright error.
        @secondary_deadlocked_count += 1
        primary_thread.set_and_wait_for_next_instruction(ContinueToThreadEnd.new)

        if @expect_nonblocking
          error_encountered ||= BlockingSynchronizationDetected.new(
            "Deadlock detected, but expect_nonblocking was set to true. Make sure you aren't "\
            "blocking waiting for a lock."
          )
        end
      end

      # Wait for the secondary thread to complete, taking note of any errors
      begin
        secondary_thread.join
      rescue => e
        # Defer exception until after the primary thread gets a chance to join, to avoid leaking
        # threads
        error_encountered ||= e
      end

      # Only now that the secondary thread has completed, release the primary thread
      primary_thread.set_and_wait_for_next_instruction(ContinueToThreadEnd.new)

      begin
        primary_thread.join
        @scenarios_run += 1
      rescue ThreadCompletedEarlyError
        # ThreadCompletedEarlyError will occur if the primary thread never successfully paused
        # at the specified location. This happens normally, when hold_primary_at_line_count is
        # incremented until it exceeds the number of lines actually executed in the primary
        # thread. Once that point is reached, the primary thread will never get caught on the
        # PauseWhenLineCount instruction. ControllableThread signals failures to execute a given
        # instruction by returning a ThreadCompletedEarlyError, which we use as a signal to stop
        # probing for race conditions. When this happens, we have done a race condition check
        # with the primary thread paused at every possible location in target_classes, assuming
        # the code in question is deterministic, so there is nothing left to check.
        done = true
      end

      # Now that both threads have had a chance to join, raise any errors discovered
      raise error_encountered if error_encountered

      check_passed = @check_blk.call(context)

      unless check_passed
        raise RaceConditionDetectedError.new("Test failed")
      end
    end
  end

  if @secondary_deadlocked_count == @scenarios_run
    message = "In every scenario, the secondary thread was assumed deadlocked while the "\
              "primary thread was paused. #{DEADLOCK_MIGHT_BE_CONFIG}"
    raise DeadlockDetectedError.new(message)
  end
end