Date: Tue, 26 Jan 2016 16:39:00 -0800 From: Luigi Rizzo <rizzo@iet.unipi.it> To: gljennjohn@gmail.com Cc: Daniel Eischen <deischen@freebsd.org>, 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: <CA%2BhQ2%2BjcGwK69jyiU3pbO4fhcnUUgA5sWm4nidb0bmGp04OD7A@mail.gmail.com> In-Reply-To: <20160127013145.36f2aaef@ernst.home> 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>
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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;
}
cheers
luigi
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