stdio line-streaming revisited

[Sean Kelly]

Andrei Alexandrescu (See Website For Email) wrote:
> kris wrote:
>> Andrei Alexandrescu (See Website For Email) wrote:
>>> kris wrote:
>>>
>>>> Andrei Alexandrescu (See Website For Email) wrote:
>>>>
>>>>> kris wrote:
>>>>>
>>>>>> Last week there were a series of posts regarding some optimized 
>>>>>> code within phobos streams. A question posed was, without those 
>>>>>> same optimizations, would tango.io be slower than the improved 
>>>>>> phobos [1]
>>>>>>
>>>>>> As these new phobos IO functions are now available, Andrei's 
>>>>>> "benchmark" [2] was run on both Win32 and linux to see where 
>>>>>> tango.io could use some improvement.
>>>>>
>>>>>
>>>>> [snip]
>>>>>
>>>>> On my machine, Tango does 4.3 seconds and the following phobos 
>>>>> program (with Walter's readln) does 5.4 seconds:
>>>>
>>>>
>>>> On Win32, the difference is very much larger. As noted before, 
>>>> several times faster. Those benefits will likely translate to linux 
>>>> going forward.
>>>
>>>
>>> If I understand things correctly, it looks like the hope is to derive 
>>> more speed from further dropping phobos and C I/O compatibility, a 
>>> path that I personally don't consider attractive.
>>
>> Nope. That's not the case at all. The expectation (or 'hope', if you 
>> like) is that we can make the linux version operate more like the 
>> Win32 version
>>
>>>
>>> Also, the fact that the tango version is "more than twice as 
>>> efficient as the fastest C version identified" suggests a problem 
>>> with the testing method or with the C code. Are they comparable? If 
>>> you genuinely have a method to push bits through two times faster 
>>> than the fastest C can do, you may want as well go ahead and patent 
>>> it. Your method would speed up many programs, since many use C's I/O 
>>> and are I/O bound. It's huge news. 
>>
>> That's good for D then?
>>
>> There's no reason why C could not take the same approach yet, one 
>> might imagine, the IO strategies exposed and the wide variety of 
>> special cases may 'discourage' the implementation of a more efficient 
>> approach? That's just pure speculation on my part, and I'm quite 
>> positive the C version could be sped up notably if one reimplemented a 
>> bunch of things.
>>
>>> I'm not even kidding. But I doubt that that's the case.
>>
>> You're most welcome to your doubts, Andrei. However, just because "C 
>> does it that way" doesn't mean it is, or ever was, the "best" approach
> 
> I think we're not on the same page here. What I'm saying is that, unless 
> you cut a deal with Microsoft to provide you with a secret D I/O API 
> that nobody knows about, all fast APIs in existence come with a C 
> interface. It's very hard to contend that. Probably you are referring to 
> the C stdio, and I'm in agreement with that. Of course there's a variety 
> of means to be faster than stdio on any given platform, at various 
> compatibility costs. It's known how to do that. "Hot water has been 
> invented."
> 
>>>>> Also, the Tango version has a bug. Running Tango's cat without any 
>>>>> pipes does not read lines from the console and outputs them one by 
>>>>> one, as it should; instead, it reads many lines and buffers them 
>>>>> internally, echoing them only after the user has pressed 
>>>>> end-of-file (^D on Linux), or possibly after the user has entered a 
>>>>> large amount of data (I didn't have the patience). The system cat 
>>>>> program and the phobos implementation correctly process each line 
>>>>> as it was entered.
>>>>
>>>>
>>>> If you mean something that you've written, that could presumeably be 
>>>> rectified by adding the isatty() test Walter had mentioned before. 
>>>> That has not been added to tango.io since (a) it would likely make 
>>>> programs behave differently depending on whether they were 
>>>> redirected or not. It's not yet clear whether that is an appropriate 
>>>> specialization, as default behaviour
>>>
>>>
>>> What is absolutely clear is that the current version has a bug. It 
>>> can't read a line from the user and write it back. There cannot be 
>>> any question that that's a problem.
>>
>> Only with the way that you've written your program. In the general 
>> case, that is not true at all. But please do submit that bug-report :)
> 
> This is the fourth time we need to discuss this. Why do I need to 
> _argue_ that this is a bug, I don't understand.
> 
> Let me spell it again: Cin.nextLine is incorrect. It cannot be used 
> (without possibly some extra incantations I don't know about) to 
> implement a program that does this:
> 
> $ ./test.d
> Please enter your name: Moe
> Hello, Moe!
> $ _

I must be missing something.  Why is the following not acceptable?

     import tango.io.Console;

     void main()
     {
         char[] name;
         Cout( "Please enter your name: " ).flush;
         Cin.nextLine( name );
         Cout( "Hello, " )( name )( "!" );
     }

> I don't have an account on the Tango site, and in a fraction of the time 
> it would take me to create one, you can submit the bug report.

True.  But it's more effective for the person who understands the 
problem to submit the bug report.

> What Win32 primitives does tango use?

ReadFile and WriteFile.


Sean