cover的原理及其启示
October 10th, 2009
原创文章，转载请注明： 转载自系统技术非业余研究
本文链接地址: cover的原理及其启示
我们先看下cover模块的功能：
The module cover provides a set of functions for coverage analysis of Erlang programs, counting how many times each executable line of code is executed when a program is run.
那它是如何做到的呢？
它是这样实现的： cover一个模块的时候要先编译， 这个过程中， 根据模块的abstract code 里面的行号，在每个有效的语句前面插入一个 ets:update_couter() 语句，这样编译出来的模块运行的时候，我们就可以收集到每个有效行的运行信息。
我hack了下cover.erl：
yu-fengdemacbook-2:src yufeng$ diff cover.erl cover_orig.erl |
1242,1243c1242 |
< {ok, Module, Binary} = compile:forms(Forms, [debug_info]), |
< io:format("abstract code: ~n~p~n", [get_abstract_code(Module, Binary)]), |
--- |
> {ok, Module, Binary} = compile:forms(Forms, []), |
yu-fengdemacbook-2:~ yufeng$ cat float.erl |
-module(float). |
-export([new/1,update/3]). |
new(N) -> |
hipe_bifs:bytearray(N*8,0). |
update(Arr,N,Float) -> |
<<A1,A2,A3,A4,A5,A6,A7,A8>> = <<Float/float>>, |
Start=N*8, |
hipe_bifs:bytearray_update(Arr,Start,A1), |
hipe_bifs:bytearray_update(Arr,Start+1,A2), |
hipe_bifs:bytearray_update(Arr,Start+2,A3), |
hipe_bifs:bytearray_update(Arr,Start+3,A4), |
hipe_bifs:bytearray_update(Arr,Start+4,A5), |
hipe_bifs:bytearray_update(Arr,Start+5,A6), |
hipe_bifs:bytearray_update(Arr,Start+6,A7), |
hipe_bifs:bytearray_update(Arr,Start+7,A8). |
yu-fengdemacbook-2:~ yufeng$ otp_src_R13B02-1/bin/erl |
Erlang R13B02 (erts-5.7.3) [source][/source][/source] [smp:2:2] [rq:2] [async-threads:0] [kernel-poll:false] |
Eshell V5.7.3 (abort with ^G) |
1> cover:start(). |
{ok,<0.33.0>} |
2> cover:compile(float). |
abstract code: |
{raw_abstract_v1, |
[{attribute,1,file,{"/Users/yufeng/float.erl",1}}, |
{attribute,1,module,float}, |
{attribute,3,export,[{new,1},{update,3}]}, |
{function,5,new,1, |
[{clause,5, |
[{var,5,'N'}], |
[], |
[{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,new}, |
{integer,0,1}, |
{integer,0,1}, |
{integer,0,6}]}, |
{integer,0,1}]}, |
%% 我们清楚的看到 ets:update_counter()的调用 |
{call,6, |
{remote,6,{atom,6,hipe_bifs},{atom,6,bytearray}}, |
[{op,6,'*',{var,6,'N'},{integer,6,8}},{integer,6,0}]}]}]}, |
{function,8,update,3, |
[{clause,8, |
[{var,8,'Arr'},{var,8,'N'},{var,8,'Float'}], |
[], |
[{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,9}]}, |
{integer,0,1}]}, |
{match,9, |
{bin,9, |
[{bin_element,9,{var,9,'A1'},default,default}, |
{bin_element,9,{var,9,'A2'},default,default}, |
{bin_element,9,{var,9,'A3'},default,default}, |
{bin_element,9,{var,9,'A4'},default,default}, |
{bin_element,9,{var,9,'A5'},default,default}, |
{bin_element,9,{var,9,'A6'},default,default}, |
{bin_element,9,{var,9,'A7'},default,default}, |
{bin_element,9,{var,9,'A8'},default,default}]}, |
{bin,9,[{bin_element,9,{var,9,'Float'},default,[float]}]}}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,10}]}, |
{integer,0,1}]}, |
{match,10, |
{var,10,'Start'}, |
{op,10,'*',{var,10,'N'},{integer,10,8}}}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,11}]}, |
{integer,0,1}]}, |
{call,11, |
{remote,11,{atom,11,hipe_bifs},{atom,11,bytearray_update}}, |
[{var,11,'Arr'},{var,11,'Start'},{var,11,'A1'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,12}]}, |
{integer,0,1}]}, |
{call,12, |
{remote,12,{atom,12,hipe_bifs},{atom,12,bytearray_update}}, |
[{var,12,'Arr'}, |
{op,12,'+',{var,12,'Start'},{integer,12,1}}, |
{var,12,'A2'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,13}]}, |
{integer,0,1}]}, |
{call,13, |
{remote,13,{atom,13,hipe_bifs},{atom,13,bytearray_update}}, |
[{var,13,'Arr'}, |
{op,13,'+',{var,13,'Start'},{integer,13,2}}, |
{var,13,'A3'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,14}]}, |
{integer,0,1}]}, |
{call,14, |
{remote,14,{atom,14,hipe_bifs},{atom,14,bytearray_update}}, |
[{var,14,'Arr'}, |
{op,14,'+',{var,14,'Start'},{integer,14,3}}, |
{var,14,'A4'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,15}]}, |
{integer,0,1}]}, |
{call,15, |
{remote,15,{atom,15,hipe_bifs},{atom,15,bytearray_update}}, |
[{var,15,'Arr'}, |
{op,15,'+',{var,15,'Start'},{integer,15,4}}, |
{var,15,'A5'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,16}]}, |
{integer,0,1}]}, |
{call,16, |
{remote,16,{atom,16,hipe_bifs},{atom,16,bytearray_update}}, |
[{var,16,'Arr'}, |
{op,16,'+',{var,16,'Start'},{integer,16,5}}, |
{var,16,'A6'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,17}]}, |
{integer,0,1}]}, |
{call,17, |
{remote,17,{atom,17,hipe_bifs},{atom,17,bytearray_update}}, |
[{var,17,'Arr'}, |
{op,17,'+',{var,17,'Start'},{integer,17,6}}, |
{var,17,'A7'}]}, |
{call,0, |
{remote,0,{atom,0,ets},{atom,0,update_counter}}, |
[{atom,0,cover_internal_data_table}, |
{tuple,0, |
[{atom,0,bump}, |
{atom,0,float}, |
{atom,0,update}, |
{integer,0,3}, |
{integer,0,1}, |
{integer,0,18}]}, |
{integer,0,1}]}, |
{call,18, |
{remote,18,{atom,18,hipe_bifs},{atom,18,bytearray_update}}, |
[{var,18,'Arr'}, |
{op,18,'+',{var,18,'Start'},{integer,18,7}}, |
{var,18,'A8'}]}]}]}, |
{eof,19}]} |
{ok,float} |
这个故事告诉我们对 erlang系统的跟踪除了trace机制以为， 我们还可以用parse transform在编译的时候加入我们想要的代码，达到跟踪， 了解系统的目的。具体的可以参考 compiler模块 parse_transform的文档。
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