Class: PEROBS::ObjectBase

Inherits:
Object
  • Object
show all
Defined in:
lib/perobs/ObjectBase.rb

Overview

Base class for all persistent objects. It provides the functionality common to all classes of persistent objects.

Direct Known Subclasses

Array, Hash, Object

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(p) ⇒ ObjectBase

New PEROBS objects must always be created by calling # Store.new(). PEROBS users should never call this method or equivalents of derived methods directly.

Parameters:



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# File 'lib/perobs/ObjectBase.rb', line 123

def initialize(p)
  _initialize(p)
end

Instance Attribute Details

#_id ⇒ Object (readonly)

Returns the value of attribute _id.



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# File 'lib/perobs/ObjectBase.rb', line 117

def _id
  @_id
end

#myself ⇒ Object (readonly)

Returns the value of attribute myself.



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# File 'lib/perobs/ObjectBase.rb', line 117

def myself
  @myself
end

#store ⇒ Object (readonly)

Returns the value of attribute store.



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# File 'lib/perobs/ObjectBase.rb', line 117

def store
  @store
end

Class Method Details

._finalize(store, id) ⇒ Object

This method generates the destructor for the objects of this class. It is done this way to prevent the Proc object hanging on to a reference to self which would prevent the object from being collected. This internal method is not intended for users to call.



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# File 'lib/perobs/ObjectBase.rb', line 147

def ObjectBase._finalize(store, id)
  proc { store._collect(id) }
end

.read(store, id) ⇒ Object

Read an raw object with the specified ID from the backing store and instantiate a new object of the specific type.



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# File 'lib/perobs/ObjectBase.rb', line 195

def ObjectBase.read(store, id)
  # Read the object from database.
  db_obj = store.db.get_object(id)

  klass = store.class_map.id_to_class(db_obj['class_id'])
  # Call the constructor of the specified class.
  obj = Object.const_get(klass).allocate
  obj._initialize(Handle.new(store, id))
  obj._deserialize(db_obj['data'])
  obj.restore

  obj
end

Instance Method Details

#==(obj) ⇒ Object

Two objects are considered equal if their object IDs are the same.



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# File 'lib/perobs/ObjectBase.rb', line 175

def ==(obj)
  return false unless obj.is_a?(ObjectBase)
  obj && @_id == obj._id
end

#_initialize(p) ⇒ Object

This is the real code for initialize. It is called from initialize() but also when we restore objects from the database. In the later case, we don’t call the regular constructors. But this code must be exercised on object creation with new() and on restore from DB. param p [PEROBS::Handle] PEROBS handle



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# File 'lib/perobs/ObjectBase.rb', line 132

def _initialize(p)
  @store = p.store
  @_id = p.id
  @store._register_in_memory(self, @_id)
  ObjectSpace.define_finalizer(self, ObjectBase._finalize(@store, @_id))
  @_stash_map = nil
  # Allocate a proxy object for this object. User code should only operate
  # on this proxy, never on self.
  @myself = POXReference.new(@store, @_id)
end

#_restore(level) ⇒ Object

Restore the object state from the storage back-end.

Parameters:

  • level (Fixnum) —

    the transaction nesting level



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# File 'lib/perobs/ObjectBase.rb', line 211

def _restore(level)
  # Find the most recently stored state of this object. This could be on
  # any previous stash level or in the regular object DB. If the object
  # was created during the transaction, there is not previous state to
  # restore to.
  data = nil
  if @_stash_map
    (level - 1).downto(0) do |lvl|
      if @_stash_map[lvl]
        data = @_stash_map[lvl]
        break
      end
    end
  end
  if data
    # We have a stashed version that we can restore from.
    _deserialize(data)
  elsif @store.db.include?(@_id)
    # We have no stashed version but can restore from the database.
    db_obj = store.db.get_object(@_id)
    _deserialize(db_obj['data'])
  end
end

#_stash(level) ⇒ Object

Save the object state for this transaction level to the storage back-end. The object gets a new ID that is stored in @_stash_map to map the stash ID back to the original data.



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# File 'lib/perobs/ObjectBase.rb', line 238

def _stash(level)
  @_stash_map ||= ::Array.new
  # Get a new ID to store this version of the object.
  @_stash_map[level] = _serialize
end

#_sync ⇒ Object

Write the object into the backing store database.



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# File 'lib/perobs/ObjectBase.rb', line 181

def _sync
  # Reset the stash map to ensure that it's reset before the next
  # transaction is being started.
  @_stash_map = nil

  db_obj = {
    'class_id' => @store.class_map.class_to_id(self.class.to_s),
    'data' => _serialize
  }
  @store.db.put_object(db_obj, @_id)
end

#_transfer(store) ⇒ Object

Library internal method to transfer the Object to a new store.

Parameters:

  • store (Store) —

    New store



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# File 'lib/perobs/ObjectBase.rb', line 153

def _transfer(store)
  @store = store
  # Remove the previously defined finalizer as it is attached to the old
  # store.
  ObjectSpace.undefine_finalizer(self)
  # Register the object as in-memory object with the new store.
  @store._register_in_memory(self, @_id)
  # Register the finalizer for the new store.
  ObjectSpace.define_finalizer(self, ObjectBase._finalize(@store, @_id))
  @myself = POXReference.new(@store, @_id)
end

#restore ⇒ Object

This method can be overloaded by derived classes to do some massaging on the data after it has been restored from the database. This could either be some sanity check or code to migrate the object from one version to another. It is also the right place to initialize non-persistent instance variables as initialize() will only be called when objects are created for the first time.



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# File 'lib/perobs/ObjectBase.rb', line 171

def restore
end