What is the BEAM?

A quick exploration will reveal the BEAM has to do with how Erlang code is executed and is the secret sauce uniting all of us - Erlang, Elixir, LFE, Efene and others. But do you really know what it is? In this talk, Michał will carefully explore the BEAM, both the runtime and the compiler. We'll see how they relate, what particular strengths this gives to our code and how we can leverage it from the applications we write every day in Erlang and Elixir. Finally, we'll see how the BEAM is similar and different to other environments and languages like Java's JVM, C#'s CLR or Lua.

Transcript

1. @michalmuskala WHAT ACTUALLY IS THE BEAM? London, 02.04.2020
2. MICHAŁ MUSKAŁA Big Tech company http://michal.muskala.eu/ https://github.com/michalmuskala/ @michalmuskala
3. @michalmuskala GLOSSARY • Erlang • Erlang/OTP • BEAM • ERTS • Elixir
4. ERLANG/OTP ERTS BEAM compiler stdlib Libraries kernel
5. @michalmuskala 1. THE VM
6. @michalmuskala QUICK HISTORY OF ERLANG • Prolog library (1986) • Joe’s Abstract Machine (1989) • Turbo Erlang Abstract Machine • Bogdan’s Erlang Abstract Machine • Virding’s Erlang Engine • Björn’s Erlang Abstract Machine
7. @michalmuskala OTHER IMPLEMENTATIONS • https://github.com/trifork/erjang • https://github.com/cloudozer/ling - Erlang on Xen • https://github.com/bettio/AtomVM • https://github.com/lumen/lumen
8. @michalmuskala WHAT IS A VIRTUAL MACHINE?
9. @michalmuskala STACK VM VS REGISTER VM Virtual Machine Showdown: Stack vs Registers https://www.usenix.org/legacy/events/vee05/full_papers/p153-yunhe.pdf
10. https://markfaction.wordpress.com/2012/07/15/stack-based-vs-register-based-virtual-machine-architecture-and-the-dalvik-vm/ STACK VS REGISTER VM PUSH 20 PUSH 7 ADD
11. https://markfaction.wordpress.com/2012/07/15/stack-based-vs-register-based-virtual-machine-architecture-and-the-dalvik-vm/ STACK VS REGISTER VM ADD R3 R1 R2 ADD R3 20 7 or
12. @michalmuskala BEAM • Register-based VM • Threaded emulator • Per-process GC with shared large-object heap • Tail recursion • First-class closures • Immutable data • No custom data types • low-level messaging primitives • NIFs/BIFs • Tracing
14. @michalmuskala PAM
15. @michalmuskala 2. THE BYTECODE
16. @michalmuskala BYTECODE • 1024 general X registers • stack slots referred to as Y registers • exchange format between the compiler and the runtime system
17. • erlc -S module.erl • mix decompile https: //github.com/michalmuskala/decompile • :erts_debug.df/1,2,3
18. LITERALS test() -> [1, 2, #{a => 5}, foo]. {function, test, 0, 2}. {label,2}. {move,{literal,[1,2, #{a => 5},foo]},{x,0}}. return.
19. STACK ALLOCATION & TAIL RECURSION defp id(x), do: x def test(a, b), do: id(id(a) + id(b)) {function, test, 2, 12}. {label,12}. {allocate,1,2}. {move,{x,1},{y,0}}. {call,1,{f,10}}. {move,{x,0},{x,1}}. {move,{y,0},{x,0}}. {move,{x,1},{y,0}}. {call,1,{f,10}}. {gc_bif,'+',{f,0},1,[{y,0},{x,0}],{x,0}}. {call_last,1,{f,10},1}.
20. MULTI-WAY BRANCH def test(x) do case x do 0 -> "zero" 1 -> "one" 2 -> "two" end end {function, test, 1, 10}. {label,10}. {test,is_integer,{f,14},[{x,0}]}. {select_val,{x,0},{f,14}, {list,[{integer,0},{f,11}, {integer,1},{f,12}, {integer,2},{f,13}]}}. {label,11}. {move,{literal, <<"zero" >>},{x,0}}. return. {label,12}. {move,{literal, <<"one" >>},{x,0}}. return. {label,13}. {move,{literal, <<"two" >>},{x,0}}. return. {label,14}. {case_end,{x,0}}.
21. @michalmuskala THE LOADER • maps .beam instructions to VM instructions • fuses some common instruction sequences • specialises instructions working on constants or registers • ops.tab and beam_makeops
22. @michalmuskala THE LOADER move S=cxy x ==0 | call Ar P=f => move_call S P i_increment rxy W t d i_plus x xy j? t d i_plus s s j? t d new_map d t I i_new_small_map_lit d t q update_map_assoc s d t I update_map_exact j? s d t I
23. LITERALS test() -> [1, 2, #{a => 5}, foo]. 00000000582FB1E8: i_func_info_IaaI 0 test test 0 00000000582FB210: move_return_c [1,2, #{a =>5},foo]
24. STACK ALLOCATION & TAIL RECURSION defp id(x), do: x def test(a, b), do: id(id(a) + id(b)) 000000001DEBA7B8: i_func_info_IaaI 0 'Elixir.Test' test 2 000000001DEBA7E0: allocate_tt 1 2 000000001DEBA7E8: move_xy x(1) y(0) 000000001DEBA7F0: i_call_f 'Elixir.Test':id/1 000000001DEBA7F8: swap_xy x(0) y(0) 000000001DEBA800: i_call_f 'Elixir.Test':id/1 000000001DEBA808: i_plus_ssjtd y(0) x(0) j(0) 1 x(0) 000000001DEBA830: i_call_last_fQ 'Elixir.Test':id/1 1
25. MULTI-WAY BRANCH def test(x) do case x do 0 -> "zero" 1 -> "one" 2 -> "two" end end 0000000014758100: i_func_info_IaaI 0 'Elixir.Test' test 1 0000000014758128: i_jump_on_val_zero_xfI x(0) f(0000000014758178) 3 f(0000000014758148) f(0000000014758168) f(0000000014758158) 0000000014758148: move_return_c <<"zero" >> 0000000014758158: move_return_c <<"two" >> 0000000014758168: move_return_c <<"one" >> 0000000014758178: case_end_x x(0)
26. @michalmuskala 3. THE COMPILER
27. @michalmuskala THE ROAD TO .BEAM Elixir Source Elixir AST Erlang Abstract Format Core Erlang Kernel Erlang BEAM SSA BEAM Erlang Source
28. ERLANG -module(test). -compile(export_all). test(sum, X, Y) -> X + Y; test(diff, X, Y) -> X - Y.
29. CORE ERLANG module 'test' ['module_info'/0, 'module_info'/1,'test'/3] attributes [ 'file' = [{[116|[101|[115|[116|[46|[101|[114|[108]]]]]]]],1}], 'compile' = ['export_all']] 'test'/3 = fun (_2,_1,_0) -> case <_2,_1,_0> of <'sum',X,Y> when 'true' -> call 'erlang':'+'(X, Y) <'diff',X,Y> when 'true' -> call 'erlang':'-'(X, Y) <_5,_4,_3> when 'true' -> primop ‘match_fail'({'function_clause',_5,_4,_3}) end 'module_info'/0 = fun () -> call 'erlang':'get_module_info'('test') 'module_info'/1 = fun (_0) -> call 'erlang':'get_module_info'('test', _0) end
30. KERNEL ERLANG fdef 'test'/3(_2, _1, _0) = match _2,_1,_0 alt select _2 type k_atom 'diff' -> do bif (remote 'erlang':'-'/2)(_1, _0) >> <_12> then <<_12 >> 'sum' -> do bif (remote 'erlang':'+'/2)(_1, _0) >> <_11> then <<_11 >> do [_0] >> <_8> then do [_1|_8] >> <_9> then do [_2|_9] >> <_10> then enter (remote 'erlang':'error'/2)('function_clause', _10) end >> <> end
31. BEAM {function, test, 3, 2}. {label,1}. {func_info,{atom,test},{atom,test},3}. {label,2}. {test,is_atom,{f,1},[{x,0}]}. {select_val,{x,0},{f,1},{list,[{atom,diff},{f,3},{atom,sum},{f,4}]}}. {label,3}. {gc_bif,’-',{f,0},3,[{x,1},{x,2}],{x,0}}. return. {label,4}. {gc_bif,'+',{f,0},3,[{x,1},{x,2}],{x,0}}. return.
32. @michalmuskala BINARY PATTERN MATCHING 89: bs_put_integer/5 90: bs_put_binary/5 91: bs_put_float/5 92: bs_put_string/2 109: bs_init2/6 111: bs_add/5 116: bs_start_match2/5 117: bs_get_integer2/7 118: bs_get_float2/7 119: bs_get_binary2/7 120: bs_skip_bits2/5 121: bs_test_tail2/3 122: bs_save2/2 123: bs_restore2/2 130: bs_context_to_binary/1 131: bs_test_unit/3 132: bs_match_string/4 133: bs_init_writable/0 134: bs_append/8 135: bs_private_append/6 137: bs_init_bits/6 138: bs_get_utf8/5 139: bs_skip_utf8/4 140: bs_get_utf16/5 141: bs_skip_utf16/4 142: bs_get_utf32/5 143: bs_skip_utf32/4 144: bs_utf8_size/3 145: bs_put_utf8/3 146: bs_utf16_size/3 147: bs_put_utf16/3 148: bs_put_utf32/3 165: bs_get_tail/3 166: bs_start_match3/4 167: bs_get_position/3 168: bs_set_position/2
33. @michalmuskala HIPE
34. @michalmuskala 4. THE COMMUNITY
36. @michalmuskala THE FUTURE
37. @michalmuskala YOU CAN PLAY WITH IT TOO • http://blog.erlang.org/ • http://blog.erlang.org/compiler-time-option/ - “Exploring the Compiler Using the 'time' Option” • http://blog.erlang.org/compiler-lost-in-translation/ - “Lost in Translation (Exploring the Compiler's Front End)” • http://blog.erlang.org/core-erlang-by-example/ - “Core Erlang by Example” • https://github.com/happi/theBeamBook - “The BEAM Book” • http://beam-wisdoms.clau.se/en/latest/ - “BEAM Wisdoms”
38. @michalmuskala WHAT ACTUALLY IS THE BEAM? London, 02.04.2020