On (03/27/17 19:28), Aleksey Makarov wrote:
[..]
> > > + /*
> > > + * Maintain an invariant that will help to find if
> > > + * the matching console is preferred, see
> > > + * register_console():
> > > + *
> > > + * The last non-braille console is always
> > > + * the preferred one.
> > > + */
> > > + for (last = MAX_CMDLINECONSOLES - 1;
> > > + last >= 0 && !console_cmdline[last].name[0];
> > > + last--)
> > > + ;
> >
> > This is a rather non-trivial code to find the last element.
> > I might make sense to count it in a global variable.
> > Then we might remove the check for console_cmdline[i].name[0]
> > also in the other for cycles and make them better readable.
>
> Having an additional variable console_cmdline_last pointing to the last element
> would require maintaining consistency between this variable and
> contents of console_cmdline. For the code we have it is not hard, but when code
> is changed we need to check this. Also there exists preferred_console that
> has almost the same meaning but it points not to the last element, but to the
> last non-braille element. Also we need to have a special value (-1) for this
> variable for empty array. So I personally would instead try to rewrite this:
>
> for (last = MAX_CMDLINECONSOLES - 1; last >= 0; last--)
> if (console_cmdline[last].name[0])
> break;
>
> Is it better? If not, I will send a version with console_cmdline_last.
personally I'm fine with the nested loop. the latest version
"for (last = MAX_CMDLINECONSOLES - 1; last >= 0;..."
is even easier to read.
so we do not just iterate console_cmdline anymore, but also modify it.
this, probably, has impact on the following scenario
CPU0 CPU1
add_preferred_console() add_preferred_console()
__add_preferred_console() __add_preferred_console()
swap(i1, last) swap(i2, last)
temp1 = i1
i1 = last temp2 = i2
last = temp1 i2 = last
last = temp2
so both i1 and i2 will point to 'last' now, IOW, we will have two
identical entries in console_cmdline, while i1 or i2 will be lost.
neither add_preferred_console() nor __add_preferred_console() have any
serialization. and I assume that we can call add_preferred_console()
concurrently, can't we?
-ss
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