Class: DynaModel::Extensions::Lock

Inherits:
Object
  • Object
show all
Includes:
Document
Defined in:
lib/dyna_model/extensions/lock.rb

Defined Under Namespace

Classes: LockNotAcquired

Constant Summary collapse

HOST = 
`hostname`.strip

Constants included from Document

Document::GUID_DELIMITER_PRECEDENCE, Document::MAX_ITEM_SIZE

Constants included from Query

Query::DEFAULT_BATCH_SIZE, Query::QUERY_TIMEOUT

Class Method Summary collapse

Methods included from Document

#all_attributes_loaded?, #dynamo_db_guid, #dynamo_db_item_key_values, #id, #load_attributes!, #to_param, #touch, #touch!

Class Method Details

.acquire(lock_name, options = {}) ⇒ Object 



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# File 'lib/dyna_model/extensions/lock.rb', line 43

def self.acquire(lock_name, options={})
  options[:acquisition_timeout] ||= 15
  options[:expires_in] ||= 10

  retries = 0
  begin
    Timeout::timeout(options[:acquisition_timeout]) do
      begin
        locked_at = DateTime.now
        expires_at = locked_at + options[:expires_in].seconds
        lock_obj = self.new(
          lock_name: lock_name,
          locked_at: locked_at,
          expires_at: expires_at,
          locked_by: self.locked_by
        )
        if lock_obj.save(expected: {
          :locked_by.null => "",
          :expires_at.le => locked_at
        }, conditional_operator: :or)
          DynaModel::Config.logger.info "Acquired lock '#{lock_name}'"
          lock_obj
        else
          raise "Error acquiring lock: #{lock_obj.errors.full_messages.to_sentence}"
        end
      rescue AWS::DynamoDB::Errors::ConditionalCheckFailedException
        DynaModel::Config.logger.info "Lock condition failed for '#{lock_name}'. Retrying..."
        sleep((2 ** retries) * 0.05)
        retries += 1
        retry
      end
    end
  rescue Timeout::Error
    raise LockNotAcquired, "Could not acquire lock after #{options[:acquisition_timeout]} seconds"
  end
end

.extend(lock_name, extension_time = 5.seconds) ⇒ Object 



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# File 'lib/dyna_model/extensions/lock.rb', line 100

def self.extend(lock_name, extension_time=5.seconds)
  locked_at = DateTime.now
  expires_at = locked_at + extension_time

  lock_obj = self.new(
    lock_name: lock_name,
    locked_at: locked_at,
    expires_at: expires_at,
    locked_by: self.locked_by
  )

  if lock_obj.save(expected: {
    :locked_by.eq => self.locked_by
  })
    DynaModel::Config.logger.info "Extended lock '#{lock_name}' for #{extension_time} seconds"
    true
  else
    raise "Error extending lock: #{lock_obj.errors.full_messages.to_sentence}"
  end
rescue AWS::DynamoDB::Errors::ConditionalCheckFailedException => e
  DynaModel::Config.logger.info "Condition failed to extend lock '#{lock_name}'"
end

.lock(lock_name, options = {}, &block) ⇒ Object 



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# File 'lib/dyna_model/extensions/lock.rb', line 28

def self.lock(lock_name, options={}, &block)
  lock_acquired = false
  if lock_obj_acquired = self.acquire(lock_name, options)
    lock_acquired = true
    if block
      begin
        result = (block.arity == 1) ? block.call(lock_obj_acquired) : block.call
      ensure
        release(lock_name) if lock_acquired
      end
    end
    result
  end
end

.locked_by ⇒ Object 



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# File 'lib/dyna_model/extensions/lock.rb', line 24

def self.locked_by
  "#{HOST}:#{Process.pid}"
end

.release(lock_name, options = {}) ⇒ Object 



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# File 'lib/dyna_model/extensions/lock.rb', line 80

def self.release(lock_name, options={})
  lock_obj = self.new(
    lock_name: lock_name,
    locked_at: nil,
    expires_at: nil,
    locked_by: nil
  )

  if lock_obj.save(expected: {
    :locked_by.eq => self.locked_by
  })
    DynaModel::Config.logger.info "Released lock '#{lock_name}'"
    true
  else
    raise "Error releasing lock: #{lock_obj.errors.full_messages.to_sentence}"
  end
rescue AWS::DynamoDB::Errors::ConditionalCheckFailedException => e
  DynaModel::Config.logger.info "Condition failed to release lock '#{lock_name}'"
end