# = PStore -- Transactional File Storage for Ruby Objects
# documentation by Kev Jackson and James Edward Gray II
# See PStore for documentation.
# PStore implements a file based persistence mechanism based on a Hash. User
# code can store hierarchies of Ruby objects (values) into the data store file
# by name (keys). An object hierarchy may be just a single object. User code
# may later read values back from the data store or even update data, as needed.
# The transactional behavior ensures that any changes succeed or fail together.
# This can be used to ensure that the data store is not left in a transitory
# state, where some values were updated but others were not.
# Behind the scenes, Ruby objects are stored to the data store file with
# Marshal. That carries the usual limitations. Proc objects cannot be
# marshalled, for example.
# # a mock wiki object...
# def initialize( page_name, author, contents )
# add_revision(author, contents)
# def add_revision( author, contents )
# @revisions << { :created => Time.now,
# :contents => contents }
# def wiki_page_references
# [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/)
# home_page = WikiPage.new( "HomePage", "James Edward Gray II",
# "A page about the JoysOfDocumentation..." )
# # then we want to update page data and the index together, or not at all...
# wiki = PStore.new("wiki_pages.pstore")
# wiki.transaction do # begin transaction; do all of this or none of it
# wiki[home_page.page_name] = home_page
# # ensure that an index has been created...
# wiki[:wiki_index] ||= Array.new
# wiki[:wiki_index].push(*home_page.wiki_page_references)
# end # commit changes to wiki data store file
# ### Some time later... ###
# wiki.transaction(true) do # begin read-only transaction, no changes allowed
# wiki.roots.each do |data_root_name|
# By default, file integrity is only ensured as long as the operating system
# (and the underlying hardware) doesn't raise any unexpected I/O errors. If an
# I/O error occurs while PStore is writing to its file, then the file will
# You can prevent this by setting <em>pstore.ultra_safe = true</em>.
# However, this results in a minor performance loss, and only works on platforms
# that support atomic file renames. Please consult the documentation for
# +ultra_safe+ for details.
# Needless to say, if you're storing valuable data with PStore, then you should
# backup the PStore files from time to time.
RDWR_ACCESS = {mode: IO::RDWR | IO::CREAT | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
RD_ACCESS = {mode: IO::RDONLY | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
WR_ACCESS = {mode: IO::WRONLY | IO::CREAT | IO::TRUNC | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze
# The error type thrown by all PStore methods.
class Error < StandardError
# Whether PStore should do its best to prevent file corruptions, even when under
# unlikely-to-occur error conditions such as out-of-space conditions and other
# unusual OS filesystem errors. Setting this flag comes at the price in the form
# This flag only has effect on platforms on which file renames are atomic (e.g.
# all POSIX platforms: Linux, MacOS X, FreeBSD, etc). The default value is false.
attr_accessor :ultra_safe
# To construct a PStore object, pass in the _file_ path where you would like
# PStore objects are always reentrant. But if _thread_safe_ is set to true,
# then it will become thread-safe at the cost of a minor performance hit.
def initialize(file, thread_safe = false)
dir = File::dirname(file)
unless File::directory? dir
raise PStore::Error, format("directory %s does not exist", dir)
if File::exist? file and not File::readable? file
raise PStore::Error, format("file %s not readable", file)
@thread_safe = thread_safe
# Raises PStore::Error if the calling code is not in a PStore#transaction.
raise PStore::Error, "not in transaction" unless @lock.locked?
# Raises PStore::Error if the calling code is not in a PStore#transaction or
# if the code is in a read-only PStore#transaction.
raise PStore::Error, "in read-only transaction" if @rdonly
private :in_transaction, :in_transaction_wr
# Retrieves a value from the PStore file data, by _name_. The hierarchy of
# Ruby objects stored under that root _name_ will be returned.
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
# This method is just like PStore#[], save that you may also provide a
# _default_ value for the object. In the event the specified _name_ is not
# found in the data store, your _default_ will be returned instead. If you do
# not specify a default, PStore::Error will be raised if the object is not
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
def fetch(name, default=PStore::Error)
if default == PStore::Error
raise PStore::Error, format("undefined root name `%s'", name)
# Stores an individual Ruby object or a hierarchy of Ruby objects in the data
# store file under the root _name_. Assigning to a _name_ already in the data
# store clobbers the old data.
# store = PStore.new("data_file.pstore")
# store.transaction do # begin transaction
# # load some data into the store...
# store[:single_object] = "My data..."
# store[:obj_heirarchy] = { "Kev Jackson" => ["rational.rb", "pstore.rb"],
# "James Gray" => ["erb.rb", "pstore.rb"] }
# end # commit changes to data store file
# *WARNING*: This method is only valid in a PStore#transaction and it cannot
# be read-only. It will raise PStore::Error if called at any other time.
# Removes an object hierarchy from the data store, by _name_.
# *WARNING*: This method is only valid in a PStore#transaction and it cannot
# be read-only. It will raise PStore::Error if called at any other time.
# Returns the names of all object hierarchies currently in the store.
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
# Returns true if the supplied _name_ is currently in the data store.
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
# Returns the path to the data store file.
# Ends the current PStore#transaction, committing any changes to the data
# store = PStore.new("data_file.pstore")
# store.transaction do # begin transaction
# # load some data into the store...
# store.commit # end transaction here, committing changes
# store[:three] = 3 # this change is never reached
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
throw :pstore_abort_transaction
# Ends the current PStore#transaction, discarding any changes to the data
# store = PStore.new("data_file.pstore")
# store.transaction do # begin transaction
# store[:one] = 1 # this change is not applied, see below...
# store[:two] = 2 # this change is not applied, see below...
# store.abort # end transaction here, discard all changes
# store[:three] = 3 # this change is never reached
# *WARNING*: This method is only valid in a PStore#transaction. It will
# raise PStore::Error if called at any other time.
throw :pstore_abort_transaction
# Opens a new transaction for the data store. Code executed inside a block
# passed to this method may read and write data to and from the data store
# At the end of the block, changes are committed to the data store
# automatically. You may exit the transaction early with a call to either
# PStore#commit or PStore#abort. See those methods for details about how
# changes are handled. Raising an uncaught Exception in the block is
# equivalent to calling PStore#abort.
# If _read_only_ is set to +true+, you will only be allowed to read from the
# data store during the transaction and any attempts to change the data will
# Note that PStore does not support nested transactions.
def transaction(read_only = false) # :yields: pstore
raise PStore::Error, "nested transaction" unless @lock.try_lock
raise PStore::Error, "nested transaction"
file = open_and_lock_file(@filename, read_only)
@table, checksum, original_data_size = load_data(file, read_only)
catch(:pstore_abort_transaction) do
save_data(checksum, original_data_size, file)
file.close if !file.closed?
# This can only occur if read_only == true.
catch(:pstore_abort_transaction) do
# Constant for relieving Ruby's garbage collector.
EMPTY_MARSHAL_DATA = Marshal.dump({})
EMPTY_MARSHAL_CHECKSUM = Digest::MD5.digest(EMPTY_MARSHAL_DATA)
# Open the specified filename (either in read-only mode or in
# read-write mode) and lock it for reading or writing.
# The opened File object will be returned. If _read_only_ is true,
# and the file does not exist, then nil will be returned.
# All exceptions are propagated.
def open_and_lock_file(filename, read_only)
file = File.new(filename, RD_ACCESS)
file.flock(File::LOCK_SH)
file = File.new(filename, RDWR_ACCESS)
file.flock(File::LOCK_EX)
# Load the given PStore file.
# If +read_only+ is true, the unmarshalled Hash will be returned.
# If +read_only+ is false, a 3-tuple will be returned: the unmarshalled
# Hash, an MD5 checksum of the data, and the size of the data.
def load_data(file, read_only)
raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
# This seems to be a newly-created file.
# This seems to be a newly-created file.
checksum = empty_marshal_checksum
size = empty_marshal_data.bytesize
checksum = Digest::MD5.digest(data)
raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
data.replace(EMPTY_STRING)
is_windows = RUBY_PLATFORM =~ /mswin|mingw|bccwin|wince/
self.class.__send__(:define_method, :on_windows?) do
def save_data(original_checksum, original_file_size, file)
if new_data.bytesize != original_file_size || Digest::MD5.digest(new_data) != original_checksum
if @ultra_safe && !on_windows?
# Windows doesn't support atomic file renames.
save_data_with_atomic_file_rename_strategy(new_data, file)
save_data_with_fast_strategy(new_data, file)
new_data.replace(EMPTY_STRING)
def save_data_with_atomic_file_rename_strategy(data, file)
temp_filename = "#{@filename}.tmp.#{Process.pid}.#{rand 1000000}"
temp_file = File.new(temp_filename, WR_ACCESS)
temp_file.flock(File::LOCK_EX)
File.rename(temp_filename, @filename)
File.unlink(temp_file) rescue nil
def save_data_with_fast_strategy(data, file)
file.truncate(data.bytesize)
# This method is just a wrapped around Marshal.dump
# to allow subclass overriding used in YAML::Store.
def dump(table) # :nodoc:
# This method is just a wrapped around Marshal.load.
# to allow subclass overriding used in YAML::Store.
def load(content) # :nodoc:
def empty_marshal_checksum
It is recommended that you Edit text format, this type of Fix handles quite a lot in one request
