atom

Overview

Package atom provides integer codes (also known as atoms) for a fixed set of frequently occurring strings

An atom is an unique ID of a frequently occurring name, it could be more effective in store and compare in O(1).

hello := atom.New("hello")

The atom value will be unique in the same process base on the creating order.

hello.Value()

The atom name/value mapping could be saved as a snapshot and serialized to the disk / database.

data, cache := atom.Save()

When new process start next time or on the remote, load those will restore the atom name/value mapping.

atom.Load(data, cache)

Install

Get and build package source.

go get -u github.com/flier/atom

Get and install generate atom command.

go install github.com/flier/atom/cmd/genatoms

Internal

An atom is a 4 bytes uint32, which contains the offset and length of the atom name in a global buffer, or the embedded short name (less than 4 bytes) in the value.

The highest bit set to 0 means the atom contains a long string in the global buffer.

+--------+--------------------------+
|0| len  |          offset          |
+--------+--------------------------+
|01234567|01234567|01234567|01234567|
+--------+--------------------------+

The hightest bit set to 1 means the atom embedded a short string in the value. The first byte must less than 0x80.

+--------+--------------------------+
|1|str[0]| str[1] | str[2] | str[3] |
+--------+--------------------------+
|1|  3   | str[0] | str[1] | str[2] |
+--------+--------------------------+
|1|  2   |        | str[0] | str[1] |
+--------+--------------------------+
|1|  1   |        |        | str[0] |
+--------+--------------------------+
|01234567|01234567|01234567|01234567|
+--------+--------------------------+

It means the maximum length of atom name is 127 bytes.

Atom.IsEmbedded will reports whether the atom embedded the name

Pregenerated Atoms

A build-in atoms buffer and cache could be generated with command:

$ genatoms -i atoms.txt -o atom.go -p atom -test

It will scan and extract all the Golang identifier from input file atoms.txt, the atom data and cache will be save to the output file atom.go with package name atom.

-case-insensitive
      case-insensitive atom (default true)
-format
      format the generated code (default true)
-i string
      read atom from the input file (default STDIN)
-o string
      write atom table to the output file (default STDOUT)
-p string
      generated package name (default "atom")
-test
      generate test table for the atom data

The extracted atom will be case insensitive by default.