Date: Wed, 27 Jan 2016 19:43:18 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: Alfred Perlstein <alfred@freebsd.org> Cc: Luigi Rizzo <rizzo@iet.unipi.it>, gljennjohn@gmail.com, threads@freebsd.org, Boris Astardzhiev <boris.astardzhiev@gmail.com>, "freebsd-net@freebsd.org" <net@freebsd.org> Subject: Re: Does FreeBSD have sendmmsg or recvmmsg system calls? Message-ID: <Pine.GSO.4.64.1601271940390.18285@sea.ntplx.net> In-Reply-To: <56A944C6.1040603@freebsd.org> References: <20160118140811.GW3942@kib.kiev.ua> <CAP=KkTzLCOnJVqt5F3ZuuZUiwkmWcne2Ynpi6-daE2jTzSBtfw@mail.gmail.com> <20160120073154.GB3942@kib.kiev.ua> <CAP=KkTx3dAUuSBrJiwNAAe%2BhHSG4j5Qp7sAcgtOgmVi8a12k1A@mail.gmail.com> <20160121093509.GK3942@kib.kiev.ua> <20160121233040.E1864@besplex.bde.org> <CAP=KkTw=ML=oPo2OgFfmor_nsL3om6HvmTQjKNMrOiU_dmWc2g@mail.gmail.com> <20160124050634.GS3942@kib.kiev.ua> <20160124100747.551f8e3f@ernst.home> <CAP=KkTyHG9Rb%2BnrDC1TDxzjUQFca9NkVp8Suo1c_-C00RUtkuQ@mail.gmail.com> <20160126134005.GD3942@kib.kiev.ua> <CA%2BhQ2%2BivWYJMDUwzdZGW88-mWzSVfPzX212sOFVmxxN0hpZ%2BQQ@mail.gmail.com> <20160126182543.64050678@ernst.home> <Pine.GSO.4.64.1601261743450.12995@sea.ntplx.net> <20160127013145.36f2aaef@ernst.home> <CA%2BhQ2%2BjcGwK69jyiU3pbO4fhcnUUgA5sWm4nidb0bmGp04OD7A@mail.gmail.com> <56A944C6.1040603@freebsd.org>
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On Wed, 27 Jan 2016, Alfred Perlstein wrote:
>
>
> On 1/26/16 4:39 PM, Luigi Rizzo wrote:
>> On Tue, Jan 26, 2016 at 4:31 PM, Gary Jennejohn <gljennjohn@gmail.com>
>> wrote:
>>> On Tue, 26 Jan 2016 17:46:52 -0500 (EST)
>>> Daniel Eischen <deischen@freebsd.org> wrote:
>>>
>>>> On Tue, 26 Jan 2016, Gary Jennejohn wrote:
>>>>
>>>>> On Tue, 26 Jan 2016 09:06:39 -0800
>>>>> Luigi Rizzo <rizzo@iet.unipi.it> wrote:
>>>>>
>>>>>> On Tue, Jan 26, 2016 at 5:40 AM, Konstantin Belousov
>>>>>> <kostikbel@gmail.com> wrote:
>>>>>>> On Mon, Jan 25, 2016 at 11:22:13AM +0200, Boris Astardzhiev wrote:
>>>>>>>> +ssize_t
>>>>>>>> +recvmmsg(int s, struct mmsghdr *__restrict msgvec, size_t vlen, int
>>>>>>>> flags,
>>>>>>>> + const struct timespec *__restrict timeout)
>>>>>>>> +{
>>>>>>>> + size_t i, rcvd;
>>>>>>>> + ssize_t ret;
>>>>>>>> +
>>>>>>>> + if (timeout != NULL) {
>>>>>>>> + fd_set fds;
>>>>>>>> + int res;
>>>>>>> Please move all local definitions to the beginning of the function.
>>>>>> This style recommendation was from 30 years ago and is
>>>>>> bad programming practice, as it tends to complicate analysis
>>>>>> for the human and increase the chance of improper usage of
>>>>>> variables.
>>>>>>
>>>>>> We should move away from this for new code.
>>>>>>
>>>>> Really? I personally find having all variables grouped together
>>>>> much easier to understand. Stumbling across declarations in the
>>>>> middle of the code in a for-loop, for example, takes me by surprise.
>>>>>
>>>>> I also greatly dislike initializing variables in their declarations.
>>>>>
>>>>> Maybe I'm just old fashioned since I have been writing C-code for
>>>>> more than 30 years.
>>>> +1
>>>>
>>>> Probably should be discouraged, but allowed on a case-by-case
>>>> basis. One could argue that if you need to declaration blocks
>>>> in the middle of code, then that code is too complex and should
>>>> be broken out into a separate function.
>>>>
>>> Right.
>>>
>>> And code like this
>>>
>>> int func(void)
>>> {
>>> int baz, zot;
>>> [some more code]
>>> if (zot < 5)
>>> {
>>> int baz = 3;
>>> [more code]
>>> }
>>> [some more code]
>>> }
>>>
>>> is even worse. The compiler (clang) seems to consider this to
>>> merely be a reinitialization of baz, but a human might be confused.
>> oh please... :)
>>
>> This is simply an inner variable shadowing the outer one
>> (which is another poor practice, flagged with -Wshadow ).
>> When you exit the scope you get the external variable
>> with its value, as you can see from the following code.
>>
>> #include <stdio.h>
>> int main(int ac, char *av[])
>> {
>> int baz = 5;
>> printf("1 baz %d\n", baz);
>> {
>> int baz = 3;
>> printf("2 baz %d\n", baz);
>> }
>> printf("3 baz %d\n", baz);
>> return 0;
>> }
>>
> I agree wholeheartedly with Luigi. I am also surprised that shadowed
> variable warnings was not more widely understood.
>
> It's time to move forward and make the code more readable and maintainable.
> Having scoped variables just makes sense. It's true that if you see very
> many of them, then it's likely time to introduce separate functions, but only
> in extreme cases, not on a case-by-case basis.
-1
It certainly doesn't make it more readable for me. It seems
like it is done out of sheer laziness as opposed to structuring
the code better.
--
DE
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