binary的常量优化
October 10th, 2009
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本文链接地址: binary的常量优化
erlang的binary在这个网络程序里面占着非常重要的地位,所以otp团队采用了非常多的优化手段包括:
1. binary操作对应着 opcode
2. 根据生命期和作用,有4种类型的binary
3. hipe优化,把bs_操作直接翻译成asm指令
4. 编译器层面消除无必须的操作。
下面的例子就是演示4的特性:
yu-fengdemacbook-2:~ yufeng$ cat bin.erl
-module(bin). -export([start/1]). start(A)-> B1= <<12>>, B2 = <<B1/binary, 5.0/float>>, B3= <<B2/binary, "yes">>, % B3的值是预先可以知道的, 无需一步步的构造 <<"abcd", 3:32,B3:128/binary,_/binary>> = <<"abcd1234",A/binary,2:32, 8773:64, "a", 5.0/float>>. % 2:32, 8773:64, "a", 5.0/float 这些都是预先知道的 直接翻译成二进制流。
yu-fengdemacbook-2:~ yufeng$ erlc +"'S'" bin.erl yu-fengdemacbook-2:~ yufeng$ cat bin.S
{module, bin}. %% version = 0 {exports, [{module_info,0},{module_info,1},{start,1}]}. {attributes, []}. {labels, 8}. {function, start, 1, 2}. {label,1}. {func_info,{atom,bin},{atom,start},1}. {label,2}. {move,{integer,0},{x,1}}. {gc_bif,byte_size,{f,0},2,[{x,0}],{x,2}}. {bs_add,{f,0},[{x,1},{x,2},1],{x,1}}. {bs_add,{f,0},[{x,1},{integer,29},1],{x,1}}. {bs_init2,{f,0},{x,1},0,1,{field_flags,[]},{x,1}}. {bs_put_string,8,{string,"abcd1234"}}. {bs_put_binary,{f,0},{atom,all},8,{field_flags,[unsigned,big]},{x,0}}. %% 一步到位 {bs_put_string,21, {string,[0,0,0,2,0,0,0,0,0,0,34,69,97,64,20,0,0,0,0,0,0]}}. {test,bs_start_match2,{f,3},[{x,1},2,0,{x,0}]}. {test,bs_match_string,{f,3},[{x,0},64,{string,[97,98,99,100,0,0,0,3]}]}. %% 一步到位 {test,bs_get_binary2, {f,3}, [{x,0}, 2, {integer,128}, 8, {field_flags,[{anno,[8,{file,"./bin.erl"}]},unsigned,big]}, {x,2}]}. {test,bs_skip_bits2, {f,3}, [{x,0}, {atom,all}, 8, {field_flags,[{anno,[8,{file,"./bin.erl"}]},unsigned,big]}]}. {test,is_eq_exact, {f,3}, [{x,2},{literal,<<12,64,20,0,0,0,0,0,0,121,101,115>>}]}. %% 一步到位 {move,{x,1},{x,0}}. return. {label,3}. {badmatch,{x,1}}. {function, module_info, 0, 5}. {label,4}. {func_info,{atom,bin},{atom,module_info},0}. {label,5}. {move,{atom,bin},{x,0}}. {call_ext_only,1,{extfunc,erlang,get_module_info,1}}. {function, module_info, 1, 7}. {label,6}. {func_info,{atom,bin},{atom,module_info},1}. {label,7}. {move,{x,0},{x,1}}. {move,{atom,bin},{x,0}}. {call_ext_only,2,{extfunc,erlang,get_module_info,2}}.
所以我们在使用binary的时候, 尽可能的利用这个特性。
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