[Experiment] Lua eXtension library with static hashing

All modifications and additional files are released into public domain.

Message on lua-l: http://lua-users.org/lists/lua-l/2020-04/msg00022.html (Refers to: https://github.com/evelance/lxlib/tree/ac4a7c85b1599ea6a588d5a371345be7032a7816)

Motivation

Lua is probably the scripting language that offers the lightest way to create fully independent execution contexts (a lua_State).

But even with the small standard library the language offers, registering all functions into the state so that the script can access them comes at a significant cost - around 90% of the total time needed to run a small pre-compiled script. Adding user-defined functions increases this cost, and dynamic loaded modules are even slower.

This experiment investigates:

1. If static hash tables can avoid this cost
2. How such modules would be written and what the implications are for scripts
3. How Lua will behave if a large amount of user-supplied functions get added.

Instructions

1. Run refresh_and_run.sh
2. The files out-lx and out-normal are benchmarks that compare the time needed to create 100K states, load the Lua standard libraries, load and execute precompiled bytecode, perform a full garbage-collection cycle and teardown the states.
3. out-lua54-normal out-lua54-lx can be used for manual testing
4. Change in Makefile: LXLIB=basex
5. Run refresh_and_run.sh
6. Now out-lx and out-lua54-lx have some more modules included (lfs and lhf.{complex, mathx, base64, ascii85})
7. Change in Makefile: LXLIB=heavy
8. Run refresh_and_run.sh (takes minutes)
9. Now out-lx and out-lua54-lx include around 100K auto-generated functions (module1 to module200 with the functions module1.m1func1 to module1.m1func200) and have an object size of around 40MB.

Sample results

Tested on a virtualized Linux 5.4.0-4-amd64, i5-2430M, 100K states

Executing test program (main.c/script.lua)

• LX lib: Lua 5.4 standard libraries
• Normal: Lua 5.4 standard libraries

./out-lx
Create states     -  1.0409s
Load libraries    -  0.1597s
Load bytecode     -  0.4913s
Execution         -  7.5180s
memory usage per state: 8KB
full gc cycle     -  0.7457s
Cleanup           -  1.1452s

./out-normal
Create states     -  1.0743s
Load libraries    - 13.6163s
Load bytecode     -  0.5637s
Execution         -  7.8426s
memory usage per state: 22KB
full gc cycle     -  0.8152s
Cleanup           -  1.8271s

• LX lib: Lua 5.4 standard libraries + LuaFileSystem + some LHF libraries

./out-lx
Create states     -  1.0495s
Load libraries    -  0.1596s
Load bytecode     -  0.4896s
Execution         -  6.4444s
memory usage per state: 8KB
full gc cycle     -  0.7956s
Cleanup           -  1.1430s

• Normal: Lua 5.4 standard libraries + require base64 (LHF)

./out-normal
Create states     -  1.0629s
Load libraries    - 11.0060s
Load bytecode     -  0.5761s
Require base64    - 40.4501s
Execution         -  7.8623s
memory usage per state: 23KB
full gc cycle     -  0.9126s
Cleanup           -  1.5989s

• LX lib: Lua 5.4 standard libraries + some LHF libraries + many auto-generated functions
• 100K functions, executable size is now almost 40MB

./out-lx 
Create states     -  1.1100s
Load libraries    -  0.1638s
Load bytecode     -  0.5040s
Execution         -  6.4105s
memory usage per state: 8KB
full gc cycle     -  0.8932s
Cleanup           -  1.2539s

Executing with the command-line interpreter

• Normal: Lua 5.4 standard libraries
• First call

$ time ./out-lua54-normal -e "print 'hello world'"
hello world

real	0m0,025s
user	0m0,000s
sys	0m0,019s

• Normal: Lua 5.4 standard libraries
• Consecutive calls

$ time ./out-lua54-normal -e "print 'hello world'"
hello world

real	0m0,010s
user	0m0,000s
sys	0m0,009s

• LX lib: Lua 5.4 standard libraries + some LHF libraries + many auto-generated functions
• 100K functions, executable size is now almost 40MB
• First call

$ time ./out-lua54-lx -e "print 'hello world'"
hello world

real	0m0,203s
user	0m0,019s
sys	0m0,112s

• LX lib: Lua 5.4 standard libraries + some LHF libraries + many auto-generated functions
• 100K functions, executable size is now almost 40MB
• Consecutive calls

$ time ./out-lua54-lx -e "print 'hello world'"
hello world

real	0m0,013s
user	0m0,000s
sys	0m0,011s