Class: PerfectQueue::SimpleDBBackend

Inherits:
Backend
  • Object
show all
Defined in:
lib/perfectqueue/backend/simpledb.rb

Constant Summary collapse

MAX_SELECT_ROW = 
4

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods inherited from Backend

#close

Constructor Details

#initialize(key_id, secret_key, domain) ⇒ SimpleDBBackend

Returns a new instance of SimpleDBBackend.



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# File 'lib/perfectqueue/backend/simpledb.rb', line 6

def initialize(key_id, secret_key, domain)
  require 'aws-sdk'
  @consistent_read = false

  @db = AWS::SimpleDB.new(
    :access_key_id => key_id,
    :secret_access_key => secret_key)

  @domain_name = domain
  @domain = @db.domains[@domain_name]
  unless @domain.exists?
    @domain = @db.domains.create(@domain_name)
  end
end

Instance Attribute Details

#consistent_read ⇒ Object

Returns the value of attribute consistent_read.



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# File 'lib/perfectqueue/backend/simpledb.rb', line 21

def consistent_read
  @consistent_read
end

Instance Method Details

#acquire(timeout, now = Time.now.to_i) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 46

def acquire(timeout, now=Time.now.to_i)
  while true
    # TODO support resource limit
    rows = 0
    @domain.items.select('timeout', 'data', 'created_at',
                        :where => "timeout <= '#{int_encode(now)}'",
                        :order => [:timeout, :asc],
                        :consistent_read => @consistent_read,
                        :limit => MAX_SELECT_ROW) {|itemdata|
      begin
        id = itemdata.name
        attrs = itemdata.attributes
        salt = attrs['created_at'].first

        if !salt || salt.empty?
          # finished/canceled task
          @domain.items[id].delete(:if=>{'created_at'=>''})

        else
          created_at = int_decode(salt)
          @domain.items[id].attributes.replace('timeout'=>int_encode(timeout),
              :if=>{'timeout'=>attrs['timeout'].first})

          data = attrs['data'].first

          return [id,salt], Task.new(id, created_at, data, nil)
        end

      rescue AWS::SimpleDB::Errors::ConditionalCheckFailed, AWS::SimpleDB::Errors::AttributeDoesNotExist
      end

      rows += 1
    }
    if rows < MAX_SELECT_ROW
      return nil
    end
  end
end

#cancel(id, delete_timeout = 3600, now = Time.now.to_i) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 107

def cancel(id, delete_timeout=3600, now=Time.now.to_i)
  salt = @domain.items[id].attributes['created_at'].first
  unless salt
    return false
  end
  token = [id,salt]
  finish(token, delete_timeout, now)
end

#finish(token, delete_timeout = 3600, now = Time.now.to_i) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 85

def finish(token, delete_timeout=3600, now=Time.now.to_i)
  begin
    id, salt = *token
    @domain.items[id].attributes.replace('timeout'=>int_encode(now+delete_timeout), 'created_at'=>'',
        :if=>{'created_at'=>salt})
    return true
  rescue AWS::SimpleDB::Errors::ConditionalCheckFailed, AWS::SimpleDB::Errors::AttributeDoesNotExist
    return false
  end
end

#list(&block) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 28

def list(&block)
  # TODO support resource limit
  @domain.items.select('timeout', 'data', 'created_at',
                      :where => "created_at != '' AND timeout > '#{int_encode(0)}'",
                      :order => [:timeout, :asc],
                      :consistent_read => @consistent_read) {|itemdata|
    id = itemdata.name
    attrs = itemdata.attributes
    next unless attrs['created_at'].first
    created_at = int_decode(attrs['created_at'].first)
    data = attrs['data'].first
    timeout = int_decode(attrs['timeout'].first)
    yield id, created_at, data, timeout, nil
  }
end

#submit(id, data, time = Time.now.to_i, resource = nil) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 116

def submit(id, data, time=Time.now.to_i, resource=nil)
  # TODO support resource limit
  begin
    @domain.items[id].attributes.replace('timeout'=>int_encode(time), 'created_at'=>int_encode(time), 'data'=>data,
        :unless=>'timeout')
    return true
  rescue AWS::SimpleDB::Errors::ConditionalCheckFailed, AWS::SimpleDB::Errors::ExistsAndExpectedValue
    return nil
  end
end

#update(token, timeout) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 96

def update(token, timeout)
  begin
    id, salt = *token
    @domain.items[id].attributes.replace('timeout'=>int_encode(timeout),
        :if=>{'created_at'=>salt})
  rescue AWS::SimpleDB::Errors::ConditionalCheckFailed, AWS::SimpleDB::Errors::AttributeDoesNotExist
    raise CanceledError, "Task id=#{id} is canceled."
  end
  nil
end

#use_consistent_read(b = true) ⇒ Object 



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# File 'lib/perfectqueue/backend/simpledb.rb', line 23

def use_consistent_read(b=true)
  @consistent_read = b
  self
end