# = PStore -- Transactional File Storage for Ruby Objects # # pstore.rb - # originally by matz # documentation by Kev Jackson and James Edward Gray II # # See PStore for documentation. require "fileutils" require "digest/md5" # # 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. # # == Usage example: # # require "pstore" # # # a mock wiki object... # class WikiPage # def initialize( page_name, author, contents ) # @page_name = page_name # @revisions = Array.new # # add_revision(author, contents) # end # # attr_reader :page_name # # def add_revision( author, contents ) # @revisions << { :created => Time.now, # :author => author, # :contents => contents } # end # # def wiki_page_references # [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/) # end # # # ... # end # # # create a new page... # 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 # # store page... # wiki[home_page.page_name] = home_page # # ensure that an index has been created... # wiki[:wiki_index] ||= Array.new # # update wiki index... # wiki[:wiki_index].push(*home_page.wiki_page_references) # end # commit changes to wiki data store file # # ### Some time later... ### # # # read wiki data... # wiki.transaction(true) do # begin read-only transaction, no changes allowed # wiki.roots.each do |data_root_name| # p data_root_name # p wiki[data_root_name] # end # end # class PStore binmode = defined?(File::BINARY) ? File::BINARY : 0 RDWR_ACCESS = File::RDWR | File::CREAT | binmode RD_ACCESS = File::RDONLY | binmode WR_ACCESS = File::WRONLY | File::CREAT | File::TRUNC | binmode # The error type thrown by all PStore methods. class Error < StandardError end # # To construct a PStore object, pass in the _file_ path where you would like # the data to be stored. # def initialize(file) dir = File::dirname(file) unless File::directory? dir raise PStore::Error, format("directory %s does not exist", dir) end if File::exist? file and not File::readable? file raise PStore::Error, format("file %s not readable", file) end @transaction = false @filename = file @abort = false end # Raises PStore::Error if the calling code is not in a PStore#transaction. def in_transaction raise PStore::Error, "not in transaction" unless @transaction end # # Raises PStore::Error if the calling code is not in a PStore#transaction or # if the code is in a read-only PStore#transaction. # def in_transaction_wr() in_transaction() raise PStore::Error, "in read-only transaction" if @rdonly end 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. # def [](name) in_transaction @table[name] end # # 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 # found. # # *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) in_transaction unless @table.key? name if default==PStore::Error raise PStore::Error, format("undefined root name `%s'", name) else return default end end @table[name] end # # 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. # # == Example: # # require "pstore" # # 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. # def []=(name, value) in_transaction_wr() @table[name] = value end # # 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. # def delete(name) in_transaction_wr() @table.delete name end # # 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. # def roots in_transaction @table.keys end # # 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. # def root?(name) in_transaction @table.key? name end # Returns the path to the data store file. def path @filename end # # Ends the current PStore#transaction, committing any changes to the data # store immediately. # # == Example: # # require "pstore" # # store = PStore.new("data_file.pstore") # store.transaction do # begin transaction # # load some data into the store... # store[:one] = 1 # store[:two] = 2 # # store.commit # end transaction here, committing changes # # store[:three] = 3 # this change is never reached # end # # *WARNING*: This method is only valid in a PStore#transaction. It will # raise PStore::Error if called at any other time. # def commit in_transaction @abort = false throw :pstore_abort_transaction end # # Ends the current PStore#transaction, discarding any changes to the data # store. # # == Example: # # require "pstore" # # 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 # end # # *WARNING*: This method is only valid in a PStore#transaction. It will # raise PStore::Error if called at any other time. # def abort in_transaction @abort = true throw :pstore_abort_transaction end # # 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 # file. # # 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 # raise a PStore::Error. # # Note that PStore does not support nested transactions. # def transaction(read_only=false) # :yields: pstore raise PStore::Error, "nested transaction" if @transaction begin @rdonly = read_only @abort = false @transaction = true value = nil new_file = @filename + ".new" content = nil unless read_only file = File.open(@filename, RDWR_ACCESS) file.flock(File::LOCK_EX) commit_new(file) if FileTest.exist?(new_file) content = file.read() else begin file = File.open(@filename, RD_ACCESS) file.flock(File::LOCK_SH) content = (File.open(new_file, RD_ACCESS) {|n| n.read} rescue file.read()) rescue Errno::ENOENT content = "" end end if content != "" @table = load(content) if !read_only size = content.size md5 = Digest::MD5.digest(content) end else @table = {} end content = nil # unreference huge data begin catch(:pstore_abort_transaction) do value = yield(self) end rescue Exception @abort = true raise ensure if !read_only and !@abort tmp_file = @filename + ".tmp" content = dump(@table) if !md5 || size != content.size || md5 != Digest::MD5.digest(content) File.open(tmp_file, WR_ACCESS) {|t| t.write(content)} File.rename(tmp_file, new_file) commit_new(file) end content = nil # unreference huge data end end ensure @table = nil @transaction = false file.close if file end value end # This method is just a wrapped around Marshal.dump. def dump(table) # :nodoc: Marshal::dump(table) end # This method is just a wrapped around Marshal.load. def load(content) # :nodoc: Marshal::load(content) end # This method is just a wrapped around Marshal.load. def load_file(file) # :nodoc: Marshal::load(file) end private # Commits changes to the data store file. def commit_new(f) f.truncate(0) f.rewind new_file = @filename + ".new" File.open(new_file, RD_ACCESS) do |nf| FileUtils.copy_stream(nf, f) end File.unlink(new_file) end end # :enddoc: if __FILE__ == $0 db = PStore.new("/tmp/foo") db.transaction do p db.roots ary = db["root"] = [1,2,3,4] ary[1] = [1,1.5] end 1000.times do db.transaction do db["root"][0] += 1 p db["root"][0] end end db.transaction(true) do p db["root"] end end