# File lib/pstore.rb, line 119
def initialize(file, thread_safe = false)
  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
  @filename = file
  @abort = false
  @ultra_safe = false
  @thread_safe = thread_safe
  @lock = Mutex.new
end

# File lib/pstore.rb, line 155
def [](name)
  in_transaction
  @table[name]
end

# File lib/pstore.rb, line 200
def []=(name, value)
  in_transaction_wr
  @table[name] = value
end

# File lib/pstore.rb, line 288
def abort
  in_transaction
  @abort = true
  throw :pstore_abort_transaction
end

# File lib/pstore.rb, line 262
def commit
  in_transaction
  @abort = false
  throw :pstore_abort_transaction
end

# File lib/pstore.rb, line 210
def delete(name)
  in_transaction_wr
  @table.delete name
end

# File lib/pstore.rb, line 169
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

# File lib/pstore.rb, line 236
def path
  @filename
end

# File lib/pstore.rb, line 231
def root?(name)
  in_transaction
  @table.key? name
end

# File lib/pstore.rb, line 221
def roots
  in_transaction
  @table.keys
end

# File lib/pstore.rb, line 311
def transaction(read_only = false)  # :yields:  pstore
  value = nil
  if !@thread_safe
    raise PStore::Error, "nested transaction" unless @lock.try_lock
  else
    begin
      @lock.lock
    rescue ThreadError
      raise PStore::Error, "nested transaction"
    end
  end
  begin
    @rdonly = read_only
    @abort = false
    file = open_and_lock_file(@filename, read_only)
    if file
      begin
        @table, checksum, original_data_size = load_data(file, read_only)

        catch(:pstore_abort_transaction) do
          value = yield(self)
        end

        if !@abort && !read_only
          save_data(checksum, original_data_size, file)
        end
      ensure
        file.close if !file.closed?
      end
    else
      # This can only occur if read_only == true.
      @table = {}
      catch(:pstore_abort_transaction) do
        value = yield(self)
      end
    end
  ensure
    @lock.unlock
  end
  value
end

# File lib/pstore.rb, line 482
def empty_marshal_checksum
  EMPTY_MARSHAL_CHECKSUM
end

# File lib/pstore.rb, line 479
def empty_marshal_data
  EMPTY_MARSHAL_DATA
end

# File lib/pstore.rb, line 135
def in_transaction
  raise PStore::Error, "not in transaction" unless @lock.locked?
end

# File lib/pstore.rb, line 142
def in_transaction_wr
  in_transaction
  raise PStore::Error, "in read-only transaction" if @rdonly
end

# File lib/pstore.rb, line 393
def load_data(file, read_only)
  if read_only
    begin
      table = load(file)
      raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
    rescue EOFError
      # This seems to be a newly-created file.
      table = {}
    end
    table
  else
    data = file.read
    if data.empty?
      # This seems to be a newly-created file.
      table = {}
      checksum = empty_marshal_checksum
      size = empty_marshal_data.bytesize
    else
      table = load(data)
      checksum = Digest::MD5.digest(data)
      size = data.bytesize
      raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash)
    end
    data.replace(EMPTY_STRING)
    [table, checksum, size]
  end
end

# File lib/pstore.rb, line 421
def on_windows?
  is_windows = RUBY_PLATFORM =~ /mswin|mingw|bccwin|wince/
  self.class.__send__(:define_method, :on_windows?) do
    is_windows
  end
  is_windows
end

# File lib/pstore.rb, line 368
def open_and_lock_file(filename, read_only)
  if read_only
    begin
      file = File.new(filename, RD_ACCESS)
      begin
        file.flock(File::LOCK_SH)
        return file
      rescue
        file.close
        raise
      end
    rescue Errno::ENOENT
      return nil
    end
  else
    file = File.new(filename, RDWR_ACCESS)
    file.flock(File::LOCK_EX)
    return file
  end
end

# File lib/pstore.rb, line 429
def save_data(original_checksum, original_file_size, file)
  new_data = dump(@table)

  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)
    else
      save_data_with_fast_strategy(new_data, file)
    end
  end

  new_data.replace(EMPTY_STRING)
end

# File lib/pstore.rb, line 444
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)
  begin
    temp_file.flock(File::LOCK_EX)
    temp_file.write(data)
    temp_file.flush
    File.rename(temp_filename, @filename)
  rescue
    File.unlink(temp_file) rescue nil
    raise
  ensure
    temp_file.close
  end
end

# File lib/pstore.rb, line 460
def save_data_with_fast_strategy(data, file)
  file.rewind
  file.write(data)
  file.truncate(data.bytesize)
end