Class: Archipelago::Treasure::Chest

Inherits:
Object
  • Object
show all
Includes:
Disco::Publishable
Defined in:
lib/archipelago/treasure.rb

Overview

A possibly remote database that only returns proxies to its contents, and thus runs all methods on its contents itself.

Has support for optimistically locked distributed serializable transactions.

Instance Method Summary collapse

Methods included from Disco::Publishable

#_dump, append_features, #initialize_publishable, #publish!, #service_id, #stop!, #valid?

Constructor Details

#initialize(options = {}) ⇒ Chest

Initialize a Chest

Will use a BerkeleyHashishProvider using treasure_chest.db in the same dir to get its hashes if not :persistence_provider is given.

Will try to recover crashed transaction every :transaction_recovery_interval seconds or TRANSACTION_RECOVERY_INTERVAL if none is given.

Will use Archipelago::Disco::Publishable by calling initialize_publishable with options.



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# File 'lib/archipelago/treasure.rb', line 242

def initialize(options = {})
  #
  # The provider of happy magic persistent hashes of different kinds.
  #
  @persistence_provider = options[:persistence_provider] || Archipelago::Hashish::BerkeleyHashishProvider.new(Pathname.new(File.expand_path(__FILE__)).parent.join("treasure_chest.db"))
  
  #
  # Use the given options to initialize the publishable
  # instance variables.
  #
  initialize_publishable(options)

  #
  # [transaction => [key => instance]]
  # To know what stuff is visible to a transaction.
  #
  @snapshot_by_transaction = {}
  @snapshot_by_transaction.extend(Archipelago::Current::Synchronized)

  #
  # [transaction => [key => when the key was read/updated/deleted]
  # To know if a transaction is ok to prepare and commit.
  #
  @timestamp_by_key_by_transaction = {}

  #
  # [transaction => [key => instance]]
  # To know what transactions were prepared but not
  # properly finished last run.
  #
  @crashed = Set.new

  initialize_seen_data

  #
  # The magical persistent map that defines how we actually 
  # store our data.
  #
  @db = @persistence_provider.get_cached_hashish("db")

  initialize_prepared(options[:transaction_recovery_interval] || TRANSACTION_RECOVERY_INTERVAL)

  CHEST_BY_SERVICE_ID[self.service_id] = self
end

Instance Method Details

#[](key, transaction = nil) ⇒ Object

Return the contents of this chest using a given key and transaction.



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# File 'lib/archipelago/treasure.rb', line 334

def [](key, transaction = nil)
  join!(transaction)

  instance = ensure_instance_with_transaction(key, transaction)
  return nil unless instance
  
  if Dubloon === instance
    return instance.join(transaction)
  else
    return Dubloon.new(key, self, transaction, self.service_id)
  end
end

#[]=(key, p1, p2 = nil) ⇒ Object

Put something into this chest with a given key, value and transaction.



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# File 'lib/archipelago/treasure.rb', line 389

def []=(key, p1, p2 = nil)
  if p2
    value = p2
    transaction = p1
  else
    value = p1
    transaction = nil
  end

  return set(key, value, transaction)
end

#abort!(transaction) ⇒ Object

Abort transaction in this Chest.



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# File 'lib/archipelago/treasure.rb', line 416

def abort!(transaction)
  assert_transaction(transaction)

  snapshot = @snapshot_by_transaction[transaction]
  #
  # Make sure nobody can modify this transaction while we
  # are aborting it.
  #
  snapshot.synchronize do
    serialized_transaction = Marshal.dump(transaction)

    #
    # If this transaction was successfully prepared
    #
    if @snapshot_by_transaction_db.include?(serialized_transaction)
      #
      # Unlock the keys that are part of it.
      #
      snapshot.each do |key, value|
        @db.unlock_on(key)
      end
      #
      # And remove it from persistent storage.
      #
      @snapshot_by_transaction_db[serialized_transaction] = nil
      #
      # And remove its timestamps from persistent storage.
      #
      @timestamp_by_key_by_transaction_db[serialized_transaction] = nil
    end
    #
    # Finally delete it from the snapshots.
    #
    @snapshot_by_transaction.delete(transaction)
    #
    # And from the timestamps.
    #
    @timestamp_by_key_by_transaction.delete(transaction)
  end
end

#active_transactions ⇒ Object

The transactions active in this Chest.



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# File 'lib/archipelago/treasure.rb', line 290

def active_transactions
  @snapshot_by_transaction.keys.clone
end

#call_instance_method(key, method, transaction, *arguments, &block) ⇒ Object

Call an instance method on whatever this chest holds at key with any transaction and args.



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# File 'lib/archipelago/treasure.rb', line 405

def call_instance_method(key, method, transaction, *arguments, &block)
  if transaction
    return call_with_transaction(key, method, transaction, *arguments, &block)
  else
    return call_without_transaction(key, method, *arguments, &block)
  end
end

#commit!(transaction) ⇒ Object

Commits transaction in this Chest.

NB: Transaction must be prepared before commit is called.

Raises:



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# File 'lib/archipelago/treasure.rb', line 519

def commit!(transaction)
  assert_transaction(transaction)
  raise IllegalCommitException.new(self, transaction) unless @snapshot_by_transaction_db.include?(Marshal.dump(transaction))

  snapshot = @snapshot_by_transaction[transaction]
  #
  # Make sure nobody can modify this transaction while we are
  # commiting it.
  #
  snapshot.synchronize do
    
    #
    # Copy each key and value from our private space to the real space
    #
    snapshot.each do |key, value|
      if value == :deleted
        @db.delete(key)
      else
        @db[key] = value
      end
    end

    #
    # Call abort! to clean up after the transaction.
    #
    abort!(transaction)
    
  end
end

#delete(key, transaction = nil) ⇒ Object

Delete the value of key within transaction.



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# File 'lib/archipelago/treasure.rb', line 350

def delete(key, transaction = nil)
  join!(transaction)

  rval = nil
  
  if transaction
    #
    # If we have a transaction we must note that it is deleted in a
    # separate space for that transaction.
    #
    snapshot = @snapshot_by_transaction[transaction]
    snapshot.synchronize do

      rval = snapshot[key]

      snapshot[key] = :deleted
      #
      # Make sure we remember when it was last changed according to our main db.
      #
      timestamps = @timestamp_by_key_by_transaction[transaction]
      timestamps[key] = @db.timestamp(key) unless timestamps.include?(key)
      
    end
  else
    #
    # Otherwise just ask our persistence provider to delete it.
    #
    @db.delete(key)
  end
  
  rval.freeze
  
  return rval
end

#each(callable) ⇒ Object

Will do callable.call(key, value) for each key-and-value pair in this Chest.

NB: This is totaly thread-unsafe, only do this for management or rescue!



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# File 'lib/archipelago/treasure.rb', line 301

def each(callable)
  @db.each(callable)
end

#evaluate!(label, timestamp, data) ⇒ Object

Evaluate data if we have not already seen label or if we have an earlier timestamp than the one given.



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# File 'lib/archipelago/treasure.rb', line 308

def evaluate!(label, timestamp, data)
  serialized_label = Marshal.dump(label)
  go = false

  if @seen_data.include?(serialized_label)
    last_timestamp, last_data = Marshal.load(@seen_data[serialized_label])
    go = true if timestamp > last_timestamp
  else
    go = true
  end

  if go
    begin
      Object.class_eval(data)
      @seen_data[serialized_label] = Marshal.dump([timestamp, data])
    rescue Exception => e
      @seen_data[serialized_label] = Marshal.load([timestamp, nil])
      puts e
      pp e.backtrace
    end
  end
end

#prepare!(transaction) ⇒ Object

Prepares transaction in this Chest.

NB: This will cause any update of the data within this transaction to block until it is either aborted or commited!



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# File 'lib/archipelago/treasure.rb', line 464

def prepare!(transaction)
  assert_transaction(transaction)

  #
  # If we dont know about this transaction then it can't very well
  # affect us.
  #
  return :unchanged unless @snapshot_by_transaction.include?(transaction)

  snapshot = @snapshot_by_transaction[transaction]
  #
  # Make sure nobody can modify this transaction while we are
  # preparing it.
  #
  snapshot.synchronize do

    #
    # Remember what locks we acquire so that we can
    # unlock them in case of failure.
    #
    locks = []
    timestamp_by_key = @timestamp_by_key_by_transaction[transaction]
    #
    # Acquire a lock on each key in the transaction
    #
    snapshot.each do |key, value|
      if @db.timestamp(key) == timestamp_by_key[key]
        @db.lock_on(key)
        locks << key
      else
        locks.each do |key|
          @db.unlock_on(key)
        end
        return :abort
      end
    end
    serialized_transaction = Marshal.dump(transaction)
    
    #
    # Dump its state to persistent storage.
    #
    @snapshot_by_transaction_db[serialized_transaction] = Marshal.dump(snapshot)
    #
    # And dump its timestamps to persistent storage
    #
    @timestamp_by_key_by_transaction_db[serialized_transaction] = Marshal.dump(timestamp_by_key)
    return :prepared
  end
end