Class: Aeternitas::Guard

Inherits:
Object
  • Object
show all
Defined in:
lib/aeternitas/guard.rb

Overview

A distributed lock that can not be acquired after being unlocked for a certain time (cooldown period). Using a database table (‘aeternitas_guard_locks`) with pessimistic locking we ensure atomicity and prevent race conditions.

Examples:

guard = Aeternitas::Guard.new("Twitter-MY_API_KEY", 5.seconds)
begin
  guard.with_lock do
    twitter_client.user_timeline('Darth_Max')
  end
rescue Twitter::TooManyRequests => e
  guard.sleep_until(e.rate_limit.reset_at)
  raise Aeternitas::Guard::GuardIsLocked.new(e.rate_limit.reset_at)
end

Defined Under Namespace

Classes: GuardIsLocked

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(id, cooldown, timeout = 10.minutes) ⇒ Aeternitas::Guard

Create a new Guard

Parameters:

  • id (String) —

    Lock id

  • cooldown (ActiveRecord::Duration) —

    Cooldown time

  • timeout (ActiveRecord::Duration) (defaults to: 10.minutes) —

    Lock timeout



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# File 'lib/aeternitas/guard.rb', line 36

def initialize(id, cooldown, timeout = 10.minutes)
  @id = id
  @cooldown = Aeternitas.test_mode? ? 0.seconds : cooldown
  @timeout = timeout
  @token = SecureRandom.hex(10)
end

Instance Attribute Details

#cooldown ⇒ ActiveSupport::Duration (readonly)

Returns cooldown time, in which the lock can’t be acquired after being released.

Returns:

  • (ActiveSupport::Duration) —

    cooldown time, in which the lock can’t be acquired after being released



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# File 'lib/aeternitas/guard.rb', line 27

class Guard
  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id = id
    @cooldown = Aeternitas.test_mode? ? 0.seconds : cooldown
    @timeout = timeout
    @token = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Tries to unlock the guard and starts the cooldown phase.
  # It only releases the lock if the token matches and the state is 'processing'.
  def unlock
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id, token: @token).lock.first
      return false unless lock&.processing?

      lock.update!(
        state: :cooldown,
        locked_until: @cooldown.from_now,
        reason: nil
      )
    end
    true
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, "duration must be an ActiveRecord::Duration" unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    retries = 0
    begin
      Aeternitas::GuardLock.transaction do
        lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first

        if lock
          if lock.locked_until > Time.current
            # Lock is still active
            raise GuardIsLocked.new(@id, lock.locked_until, lock.reason)
          else
            # Lock has expired
            lock.update!(
              token: @token,
              state: :processing,
              locked_until: @timeout.from_now,
              reason: nil
            )
          end
        else
          # Create new lock
          Aeternitas::GuardLock.create!(
            lock_key: @id,
            token: @token,
            state: :processing,
            locked_until: @timeout.from_now
          )
        end
      end
    rescue ActiveRecord::RecordNotUnique
      # prevent infinite loops in unexpected scenarios
      retries += 1
      raise if retries > 4
      retry
    end
  end

  # Lets the guard sleep until the given time.
  # This will create a new sleeping lock or update an existing one.
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    sleep_timeout = Time.now if Aeternitas.test_mode?
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first_or_initialize

      lock.assign_attributes(
        token: @token,
        state: :sleeping,
        locked_until: sleep_timeout,
        reason: msg
      )

      lock.save!
    end
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#id ⇒ String (readonly)

Returns the guards id.

Returns:

  • (String) —

    the guards id



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# File 'lib/aeternitas/guard.rb', line 27

class Guard
  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id = id
    @cooldown = Aeternitas.test_mode? ? 0.seconds : cooldown
    @timeout = timeout
    @token = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Tries to unlock the guard and starts the cooldown phase.
  # It only releases the lock if the token matches and the state is 'processing'.
  def unlock
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id, token: @token).lock.first
      return false unless lock&.processing?

      lock.update!(
        state: :cooldown,
        locked_until: @cooldown.from_now,
        reason: nil
      )
    end
    true
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, "duration must be an ActiveRecord::Duration" unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    retries = 0
    begin
      Aeternitas::GuardLock.transaction do
        lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first

        if lock
          if lock.locked_until > Time.current
            # Lock is still active
            raise GuardIsLocked.new(@id, lock.locked_until, lock.reason)
          else
            # Lock has expired
            lock.update!(
              token: @token,
              state: :processing,
              locked_until: @timeout.from_now,
              reason: nil
            )
          end
        else
          # Create new lock
          Aeternitas::GuardLock.create!(
            lock_key: @id,
            token: @token,
            state: :processing,
            locked_until: @timeout.from_now
          )
        end
      end
    rescue ActiveRecord::RecordNotUnique
      # prevent infinite loops in unexpected scenarios
      retries += 1
      raise if retries > 4
      retry
    end
  end

  # Lets the guard sleep until the given time.
  # This will create a new sleeping lock or update an existing one.
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    sleep_timeout = Time.now if Aeternitas.test_mode?
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first_or_initialize

      lock.assign_attributes(
        token: @token,
        state: :sleeping,
        locked_until: sleep_timeout,
        reason: msg
      )

      lock.save!
    end
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#timeout ⇒ ActiveSupport::Duration (readonly)

Returns the locks timeout duration.

Returns:

  • (ActiveSupport::Duration) —

    the locks timeout duration



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# File 'lib/aeternitas/guard.rb', line 27

class Guard
  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id = id
    @cooldown = Aeternitas.test_mode? ? 0.seconds : cooldown
    @timeout = timeout
    @token = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Tries to unlock the guard and starts the cooldown phase.
  # It only releases the lock if the token matches and the state is 'processing'.
  def unlock
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id, token: @token).lock.first
      return false unless lock&.processing?

      lock.update!(
        state: :cooldown,
        locked_until: @cooldown.from_now,
        reason: nil
      )
    end
    true
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, "duration must be an ActiveRecord::Duration" unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    retries = 0
    begin
      Aeternitas::GuardLock.transaction do
        lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first

        if lock
          if lock.locked_until > Time.current
            # Lock is still active
            raise GuardIsLocked.new(@id, lock.locked_until, lock.reason)
          else
            # Lock has expired
            lock.update!(
              token: @token,
              state: :processing,
              locked_until: @timeout.from_now,
              reason: nil
            )
          end
        else
          # Create new lock
          Aeternitas::GuardLock.create!(
            lock_key: @id,
            token: @token,
            state: :processing,
            locked_until: @timeout.from_now
          )
        end
      end
    rescue ActiveRecord::RecordNotUnique
      # prevent infinite loops in unexpected scenarios
      retries += 1
      raise if retries > 4
      retry
    end
  end

  # Lets the guard sleep until the given time.
  # This will create a new sleeping lock or update an existing one.
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    sleep_timeout = Time.now if Aeternitas.test_mode?
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first_or_initialize

      lock.assign_attributes(
        token: @token,
        state: :sleeping,
        locked_until: sleep_timeout,
        reason: msg
      )

      lock.save!
    end
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#token ⇒ String (readonly)

Returns cryptographic token which ensures we do not lock/unlock a guard held by another process.

Returns:

  • (String) —

    cryptographic token which ensures we do not lock/unlock a guard held by another process



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# File 'lib/aeternitas/guard.rb', line 27

class Guard
  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id = id
    @cooldown = Aeternitas.test_mode? ? 0.seconds : cooldown
    @timeout = timeout
    @token = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Tries to unlock the guard and starts the cooldown phase.
  # It only releases the lock if the token matches and the state is 'processing'.
  def unlock
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id, token: @token).lock.first
      return false unless lock&.processing?

      lock.update!(
        state: :cooldown,
        locked_until: @cooldown.from_now,
        reason: nil
      )
    end
    true
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, "duration must be an ActiveRecord::Duration" unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    retries = 0
    begin
      Aeternitas::GuardLock.transaction do
        lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first

        if lock
          if lock.locked_until > Time.current
            # Lock is still active
            raise GuardIsLocked.new(@id, lock.locked_until, lock.reason)
          else
            # Lock has expired
            lock.update!(
              token: @token,
              state: :processing,
              locked_until: @timeout.from_now,
              reason: nil
            )
          end
        else
          # Create new lock
          Aeternitas::GuardLock.create!(
            lock_key: @id,
            token: @token,
            state: :processing,
            locked_until: @timeout.from_now
          )
        end
      end
    rescue ActiveRecord::RecordNotUnique
      # prevent infinite loops in unexpected scenarios
      retries += 1
      raise if retries > 4
      retry
    end
  end

  # Lets the guard sleep until the given time.
  # This will create a new sleeping lock or update an existing one.
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    sleep_timeout = Time.now if Aeternitas.test_mode?
    Aeternitas::GuardLock.transaction do
      lock = Aeternitas::GuardLock.where(lock_key: @id).lock.first_or_initialize

      lock.assign_attributes(
        token: @token,
        state: :sleeping,
        locked_until: sleep_timeout,
        reason: msg
      )

      lock.save!
    end
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

Instance Method Details

#sleep_for(duration, msg = nil) ⇒ Object

Locks the guard for the given duration.

Parameters:

  • duration (ActiveSupport::Duration) —

    sleeping duration

  • msg (String) (defaults to: nil) —

    hint why the guard sleeps

Raises:

  • (ArgumentError) 


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# File 'lib/aeternitas/guard.rb', line 85

def sleep_for(duration, msg = nil)
  raise ArgumentError, "duration must be an ActiveRecord::Duration" unless duration.is_a?(ActiveSupport::Duration)
  sleep_until(duration.from_now, msg)
end

#sleep_until(until_time, msg = nil) ⇒ Object

Locks the guard until the given time.

Parameters:

  • until_time (Time) —

    sleep time

  • msg (String) (defaults to: nil) —

    hint why the guard sleeps



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# File 'lib/aeternitas/guard.rb', line 77

def sleep_until(until_time, msg = nil)
  sleep(until_time, msg)
end

#unlock ⇒ Object

Tries to unlock the guard and starts the cooldown phase. It only releases the lock if the token matches and the state is ‘processing’.



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# File 'lib/aeternitas/guard.rb', line 59

def unlock
  Aeternitas::GuardLock.transaction do
    lock = Aeternitas::GuardLock.where(lock_key: @id, token: @token).lock.first
    return false unless lock&.processing?

    lock.update!(
      state: :cooldown,
      locked_until: @cooldown.from_now,
      reason: nil
    )
  end
  true
end

#with_lock ⇒ Object

Runs a given block if the lock can be acquired and releases the lock afterwards.

Examples:

Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }

Raises:



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# File 'lib/aeternitas/guard.rb', line 48

def with_lock
  acquire_lock!
  begin
    yield
  ensure
    unlock
  end
end