On Mon, Apr 22, 2013 at 9:21 PM, Nathan Rajlich <[email protected]>wrote:
> I'd vote D, because then .writev() could accept an Array of these "chunk
> objects" and/or Buffer instances (which don't need "encoding" specified).
> That way, if you're just writing Buffer instances, it would be the logical:
>
> stream.writev([ buf1, buf2, buf3 ], callback);
>
Do you mean C?
I rather like the C/D family of options, though given the choice I'd go
with option E, a small tweak to more closely mirrors the signature of
stream.write...
stream.writev([ [ buf1 ], [ buf2, "ignored" ], [ str1, 'ascii' ] ],
callback);
It'd just be an array of tuples where the second arg is ignored if the
first arg is a buffer.
>
> On Mon, Apr 22, 2013 at 5:01 PM, Isaac Schlueter <[email protected]> wrote:
>
>> There's a syscall called `writev` that lets you write an array (ie,
>> "Vector") of buffers of data rather than a single buffer.
>>
>> I'd like to support something like this for Streams in Node, mostly
>> because it will allow us to save a lot of TCP write() calls, without
>> having to copy data around, especially for chunked encoding writes.
>> (We write a lot of tiny buffers for HTTP, it's kind of a nightmare,
>> actually.)
>>
>> Fedor Indutny has already done basically all of the legwork to
>> implement this. Where we're stuck is the API surface, and here are
>> some options. Node is not a democracy, but your vote counts anyway,
>> especially if it's a really good vote with some really good argument
>> behind it :)
>>
>> Goals:
>> 1. Make http more good.
>> 2. Don't break existing streams.
>> 3. Don't make things hard.
>> 4. Don't be un-node-ish
>>
>> For all of these, batched writes will only be available if the
>> Writable stream implements a `_writev()` method. No _writev, no
>> batched writes. Any bulk writes will just be passed to _write(chunk,
>> encoding, callback) one at a time in the order received.
>>
>> In all cases, any queued writes will be passed to _writev if that
>> function is implemented, even if they're just backed up from a slow
>> connection.
>>
>>
>> Ideas:
>>
>>
>> A) stream.bulk(function() { stream.write('hello');
>> stream.write('world'); stream.end('!\n') })
>>
>> Any writes done in the function passed to `stream.bulk()` will be
>> batched into a single writev.
>>
>> Upside:
>> - Easier to not fuck up and stay frozen forever. There is basically
>> zero chance that you'll leave the stream in a corked state. (Same
>> reason why domain.run() is better than enter()/exit().)
>>
>> Downsides:
>> - easier to fuck up and not actually batch things. eg,
>> s.bulk(function(){setTimeout(...)})
>> - bulk is a weird name. "batch" maybe? Nothing else really seems
>> appropriate either.
>> - somewhat inflexible, since all writes have to be done in the same
>> function call
>>
>>
>> B) stream.cork(); stream.write('hello'); stream.write('world');
>> stream.end('!\n'); stream.uncork();
>>
>> Any writes done while corked will be flushed to _writev() when uncorked.
>>
>> Upside:
>> - Easy to implement
>> - Strictly more flexible than stream.bulk(writer). (Can trivially
>> implement a bulk function using cork/uncork)
>> - Useful for cases outside of writev (like corking a http request
>> until the connection is established)
>>
>> Downsides:
>> - Easy to fuck up and stay corked forever.
>> - Two functions instead of just one (double the surface area increase)
>>
>>
>> C) stream.writev([chunks,...], [encodings,...], callback)
>>
>> That is, implement a first-class top-level function called writev()
>> which you can call with an array of chunks and an array of encodings.
>>
>> Upside:
>> - No unnecessary surface area increase
>> - NOW IT'S YOUR PROBLEM, NOT MINE, HAHA! (Seriously, though, it's
>> less magical, simpler stream.Writable implementation, etc.)
>>
>> Downside:
>> - A little bit tricky when you don't already have a list of chunks to
>> send. (For example, with cork, you could write a bunch of stuff into
>> it, and then uncork all at the end, and do one writev, even if it took
>> a few ms to get it all.)
>> - parallel arrays, ew.
>>
>>
>> D) stream.writev([ {chunk:buf, encoding: blerg}, ...], callback)
>>
>> That is, same as C, but with an array of {chunk,encoding} objects
>> instead of the parallel arrays.
>>
>> Same +/- as C, except the parallel array bit. This is probably how
>> we'd call the implementation's stream._writev() anyway, so it'd be a
>> bit simpler.
>>
>>
>>
>> Which of these seems like it makes the most sense to you?
>>
>> Is there another approach that you'd like to see here? (Note: "save
>> all writes until end of tick always" and "copy into one big buffer"
>> approaches are not feasible for obvious performance reasons.)
>>
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