method

transaction

v1_8_6_287 - Show latest stable - 0 notes - Class: PStore

transaction(read_only=false) public

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.

Show source

# File lib/pstore.rb, line 284
  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

transaction

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