Re: [Tarantool-patches] [PATCH luajit 4/7][v2] sysprof: introduce specific errors and default mode

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hi, Sergey,

thanks for review!

On 18.02.2025 18:43, Sergey Kaplun via Tarantool-patches wrote:
> Hi, Sergey!
> Thanks for the fixes!
> After refactoring the code become more readable, thanks!
> Now I have a few ideas, see my comments below.
>
> On 13.02.25, Sergey Bronnikov wrote:
>> sysprof has a number of options and with any incorrect option it
>> returns `false` and error message "profiler misuse". This message
>> discourage sysprof users and make using sysprof more complicated.
> Typo: s/discourage/discourages/
> Typo: s/make/makes/
Fixed.
>
>> The patch sets default profiling mode ("D", that shows only
> Typo: s/default/the default/
Fixed.
>
>> virtual machine state counters) if it was not passed and adds
>> details to the error message with possible reasons of misuse.
>> ---
>>   src/lib_misc.c                                | 80 +++++++++++++------
>>   src/lj_errmsg.h                               |  5 ++
>>   .../profilers/misclib-sysprof-lapi.test.lua   | 48 +++++++++--
>>   3 files changed, 100 insertions(+), 33 deletions(-)
>>
>> diff --git a/src/lib_misc.c b/src/lib_misc.c
>> index 5b7a4b62..d71904e4 100644
>> --- a/src/lib_misc.c
>> +++ b/src/lib_misc.c
>> @@ -163,6 +163,7 @@ static int on_stop_cb_default(void *opt, uint8_t *buf)
>>   
>>   /* The default profiling interval equals to 10 ms. */
>>   #define SYSPROF_DEFAULT_INTERVAL 10
>> +#define SYSPROF_DEFAULT_MODE "D"
>>   #define SYSPROF_DEFAULT_OUTPUT "sysprof.bin"
>>   
>>   static int set_output_path(const char *path, struct luam_Sysprof_Options *opt) {
>> @@ -177,21 +178,41 @@ static int set_output_path(const char *path, struct luam_Sysprof_Options *opt) {
>>     return PROFILE_SUCCESS;
>>   }
>>   
>> -static int parse_sysprof_opts(lua_State *L, struct luam_Sysprof_Options *opt, int idx) {
>> -  GCtab *options = lj_lib_checktab(L, idx);
>> +static int parse_sysprof_opts(lua_State *L, struct luam_Sysprof_Options *opt,
>> +	                          const char **err_details) {
>> +  int n = (int)(L->top - L->base);
>> +  if (n != 1) {
> I suppose this should be `n == 0`. Otherwise we will observe the
> following behaviour:
> | src/luajit -e 'print(misc.sysprof.start(1, 2, 3))'
> | true
Right, fixed.
>> +    opt->mode = LUAM_SYSPROF_DEFAULT;
>> +    opt->interval = SYSPROF_DEFAULT_INTERVAL;
>> +    goto set_path;
> I suppose it is better to set path explicitly here and goto ctx_allocate;

The code that make a jump to the middle of basic block smells bad.

It makes control flow more complicated, and benefits are not obvious.

>
>> +  }
>> +
>> +  if (!lua_istable(L, 1)) {
> The more I think about it, the more it looks like a bug -- all library
> functions raise an error when they get a bad parameter type.
>
> Maybe we should just use `lj_lib_checktab()` here? This will help the
> user to find an error and be consistent with memprof behaviour. So,
> bugfix isn't breaking change, since something is working incorrectly.
> Plus, as a bonus we don't need to introduce the new error with the same
> meaning we have already.
>
> OTOH, if you are against it, we may leave it as is, but check it via
> `tvistab()` instead.
>
> What do you think?
>
> And the same should be done with the parameters in table content --
> their type should be checked at once and the corresponding error should
> be raised. I suppose we can introduce a local (inside this translation
> unit) helper `key_opt_type()` here -- we will check a type for the keys
> `path`, `mode`, `interval` and raise the user-friendly error like:

What for? The reason of this patch series is bad error handling in 
profilers.

The value behind this refactoring is not obvious. Please elaborate.

This code was imperfect for about 2-3 years and this was ok for everyone

who added it initially. I don't want to fix all bad places here, just 
improve error messages visible by end users.

>
> `bad key 'mode' in 'start' argument (string expected, got table)`.
> See how it is done in `lj_lib_check*()` for inspiration.
>
>> +    *err_details = err2msg(LJ_ERR_PROF_DETAILS_BADTABLE);
>> +    return PROFILE_ERRUSE;
>> +  }
>> +
>> +  GCtab *options = lj_lib_checktab(L, 1);
> This check is excess, let's move it above, as I suggested.

it is not a check, it's a function that retrieves a table from the stack.

>
>>   
>>     /* Get profiling mode. */
>>     {
>>       const char *mode = NULL;
>>   
>>       cTValue *mode_opt = lj_tab_getstr(options, lj_str_newlit(L, "mode"));
>> -    if (!mode_opt || !tvisstr(mode_opt)) {
>> -      return PROFILE_ERRUSE;
>> +    if (mode_opt) {
>> +      if (!tvisstr(mode_opt)) {
>> +        *err_details = err2msg(LJ_ERR_PROF_DETAILS_BADMODE);
>> +        return PROFILE_ERRUSE;
>> +      }
>> +      mode = strVdata(mode_opt);
>> +      if (strlen(mode) > 0 && mode[1] != '\0') {
> Minor: It's better to use `(strlen(mode) == 0) || mode[1] != '\0'` -- we
> don't got further in code below, just early return here.

Fixed.


>
>> +        *err_details = err2msg(LJ_ERR_PROF_DETAILS_BADMODE);
>> +        return PROFILE_ERRUSE;
>> +      }
>>       }
>>   
> <snipped>
>
>> +set_path:
>> +
>>     /* Get output path. */
>>     if (opt->mode != LUAM_SYSPROF_DEFAULT)
>>     {
>> @@ -230,8 +256,10 @@ static int parse_sysprof_opts(lua_State *L, struct luam_Sysprof_Options *opt, in
>>       cTValue *pathtv = lj_tab_getstr(options, lj_str_newlit(L, "path"));
>>       if (!pathtv)
>>         path = SYSPROF_DEFAULT_OUTPUT;
>> -    else if (!tvisstr(pathtv))
>> +    else if (!tvisstr(pathtv)) {
> It is better to wrap if and else branches too like the following:
> | if () {
> | } else if () {
> | } else {
> | }

It's funny, on the previous review brackets were excess [1].

1. https://lists.tarantool.org/tarantool-patches/Z6XlUsKqu92__8fL@root/T/#t

Brackets are not needed in the first and third blocks, if we're 
following a rule "brackets for blocks with more than one statements".
>
>> +      *err_details = err2msg(LJ_ERR_PROF_DETAILS_BADPATH);
>>         return PROFILE_ERRUSE;
>> +    }
>>       else
>>         path = strVdata(pathtv);
>>   
>> @@ -251,29 +279,28 @@ static int parse_sysprof_opts(lua_State *L, struct luam_Sysprof_Options *opt, in
>>     return PROFILE_SUCCESS;
>>   }
>>   
>> -static int parse_options(lua_State *L, struct luam_Sysprof_Options *opt)
>> -{
>> -  if (lua_gettop(L) != 1)
>> -    return PROFILE_ERRUSE;
>> -
>> -  if (!lua_istable(L, 1))
>> -    return PROFILE_ERRUSE;
>> -
>> -  return parse_sysprof_opts(L, opt, 1);
>> -}
>> -
>> -static int sysprof_error(lua_State *L, int status)
>> +static int sysprof_error(lua_State *L, int status, const char *err_details)
>>   {
>>     switch (status) {
>>       case PROFILE_ERRUSE:
>>         lua_pushnil(L);
>>         lua_pushstring(L, err2msg(LJ_ERR_PROF_MISUSE));
>> +      if (err_details) {
>> +        lua_pushstring(L, ": ");
> I suppose we may use string formatting here instead of concatenation Lua
> C API call:
> See usage of `lj_strfmt_pushf()` for the details.

Sure, we may, but what for?

Previous functions are a part of Lua C API (lua_pushnil, lua_pushstring),

why do we need to mix Lua C functions with this LJ-specific function?

> Also, we may use nice helper to avoid code copy-pasting.
>
>> +        lua_pushstring(L, err_details);
>> +        lua_concat(L, 3);
>> +      }
>>         lua_pushinteger(L, EINVAL);
>>         return 3;
>>   #if LJ_HASSYSPROF
>>       case PROFILE_ERRRUN:
>>         lua_pushnil(L);
>>         lua_pushstring(L, err2msg(LJ_ERR_PROF_ISRUNNING));
>> +      if (err_details) {
>> +        lua_pushstring(L, ": ");
>> +        lua_pushstring(L, err_details);
>> +        lua_concat(L, 3);
>> +      }
>>         lua_pushinteger(L, EINVAL);
>>         return 3;
>>       case PROFILE_ERRIO:
>> @@ -291,15 +318,16 @@ LJLIB_CF(misc_sysprof_start)
> <snipped>
>
>> diff --git a/src/lj_errmsg.h b/src/lj_errmsg.h
>> index 19c41f0b..b5c3a275 100644
>> --- a/src/lj_errmsg.h
>> +++ b/src/lj_errmsg.h
>> @@ -188,6 +188,11 @@ ERRDEF(PROF_ISRUNNING,	"profiler is running already")
>>   ERRDEF(PROF_NOTRUNNING,	"profiler is not running")
>>   #endif
>>   
>> +ERRDEF(PROF_DETAILS_BADMODE, "profiler mode must be 'D', 'L' or 'C'")
>> +ERRDEF(PROF_DETAILS_BADINTERVAL, "profiler interval must be greater than 1")
>> +ERRDEF(PROF_DETAILS_BADPATH, "profiler path does not exist")
>> +ERRDEF(PROF_DETAILS_BADTABLE, "profiler expects a table with parameters")
>> +
> These changes should be under the LJ_HASSYSPROF ifdef.
> Also, I suggest the following naming:
> | SYSPROF_BADMODE
> | SYSPROF_BADINTERVAL
> With this it will be obviour that they are sysprof-specific and not too
> long.

Imagine you then introduce a table and interval number for memprof.

Will you rename constants back? I dislike your suggestion.

>
>>   #undef ERRDEF
>>   
>>   /* Detecting unused error messages:
>> diff --git a/test/tarantool-tests/profilers/misclib-sysprof-lapi.test.lua b/test/tarantool-tests/profilers/misclib-sysprof-lapi.test.lua
>> index 32fa384c..7622323a 100644
>> --- a/test/tarantool-tests/profilers/misclib-sysprof-lapi.test.lua
>> +++ b/test/tarantool-tests/profilers/misclib-sysprof-lapi.test.lua
>> @@ -10,7 +10,7 @@ local test = tap.test("misclib-sysprof-lapi"):skipcond({
>>     ["Disabled due to #10803"] = os.getenv("LUAJIT_TEST_USE_VALGRIND"),
>>   })
>>   
>> -test:plan(19)
>> +test:plan(33)
>>   
>>   jit.off()
>>   -- XXX: Run JIT tuning functions in a safe frame to avoid errors
>> @@ -65,10 +65,25 @@ end
>>   
>>   -- Wrong profiling mode.
>>   local res, err, errno = misc.sysprof.start{ mode = "A" }
>> -test:ok(res == nil anderr:match("profiler misuse"),
>> -        "result status with wrong profiling mode")
>> +test:ok(res == nil, "result status with wrong profiling mode")
>> +test:ok(err:match("profiler mode must be 'D', 'L' or 'C'"),
>> +        "error with wrong profiling mode")
> I would rather still check matching with `profiler misuse:` error (as a
> separate testcase). Here and below. But it's up to you. Feel free to
> ignore.
I think that checking specific part of error message is enough.
>
>>   test:ok(type(errno) == "number", "errno with wrong profiling mode")
>>   
>> +-- Missed profiling mode.
>> +res, err, errno = misc.sysprof.start{}
>> +test:is(res, true, "res with missed profiling mode")
>> +test:is(err, nil, "no error with missed profiling mode")
>> +test:is(errno, nil, "no errno with missed profiling mode")
>> +assert(misc.sysprof.stop())
>> +
>> +-- Not a table.
> This should be changed to the pcall() after the changes I suggested.
>
>> +res, err, errno = misc.sysprof.start("NOT A TABLE")
>> +test:ok(res == nil, "res with not a table")
>> +test:ok(err:match("profiler expects a table with parameters"),
>> +        "error with not a table")
>> +test:ok(type(errno) == "number", "errno with not a table")
> Please also check the case with multiple arguments (2 cases: all
> invalid, and only first valid).

Added:

254: ok - res with all invalid parameters
254: ok - error with all invalid parameters
254: ok - errno with all invalid parameters
254: ok - res with all invalid parameters except the first one
254: ok - error with all invalid parameters except the first one
254: ok - errno with all invalid parameters except the first one


>
>> +
>>   -- Already running.
>>   res, err = misc.sysprof.start{ mode = "D" }
>>   assert(res, err)
>> @@ -92,11 +107,30 @@test:ok(res == nil anderr:match("No such file or directory"),
>>           "result status and error with bad path")
>>   test:ok(type(errno) == "number", "errno with bad path")
>>   
>> --- Bad interval.
>> +-- Bad interval (-1).
>>   res, err, errno = misc.sysprof.start{ mode = "C", interval = -1 }
>> -test:ok(res == nil anderr:match("profiler misuse"),
>> -        "result status and error with bad interval")
>> -test:ok(type(errno) == "number", "errno with bad interval")
>> +test:is(res, nil, "result status and error with bad interval -1")
>> +test:ok(err:match("profiler interval must be greater than 1"),
>> +        "error with bad interval -1")
>> +test:ok(type(errno) == "number", "errno with bad interval -1")
>> +
>> +-- Bad interval (0).
>> +res, err, errno = misc.sysprof.start{ mode = "C", interval = 0 }
>> +test:ok(res == nil, "res with bad interval 0")
>> +test:ok(err:match("profiler interval must be greater than 1"),
>> +        "error with bad interval 0")
>> +test:ok(type(errno) == "number", "errno with bad interval 0")
>> +
>> +-- Good interval (1).
>> +res, err, errno = misc.sysprof.start{
> Minor: Please use brackets for functions call.

Case without brackets is more popular:

   local res, err = misc.sysprof.start(opts)
   res,err = misc.sysprof.stop()
local res, err, errno = misc.sysprof.start{ mode = "A" }
res, err, errno = misc.sysprof.start{}
assert(misc.sysprof.stop())
res, err, errno = misc.sysprof.start("NOT A TABLE")
res, err = misc.sysprof.start{ mode = "D" }
res, err, errno = misc.sysprof.start{ mode = "D" }
res, err = misc.sysprof.stop()
res, err, errno = misc.sysprof.stop()
res, err, errno = misc.sysprof.start({ mode = "C", path = BAD_PATH })
res, err, errno = misc.sysprof.start{ mode = "C", interval = -1 }
res, err, errno = misc.sysprof.start{ mode = "C", interval = 0 }
res, err, errno = misc.sysprof.start{
misc.sysprof.stop()
local report = misc.sysprof.report()
report = misc.sysprof.report()

proposed change will make coding style inconsistent in the file

>
>> +    mode = "C",
>> +    interval = 1,
>> +    path = "/dev/null",
>> +}
>> +test:is(res, true, "res with good interval 1")
>> +test:is(err, nil, "no error with good interval 1")
>> +test:is(errno, nil, "no errno with good interval 1")
>> +misc.sysprof.stop()
>>   
>>   -- DEFAULT MODE
>>   
>> -- 
>> 2.34.1
>>

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