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  1.  Home
  2. WEB400
  3. October 2015

Re: Why does node's Toolkit for i, use a database connection to execute CL commands?

I guess what I mean is if it is in a callback then the very next line of code gets executed instantly, so in that respect you would not notice it.

Sent from my iPad

On 13 Oct 2015, at 22:05, Aaron Bartell <aaronbartell@xxxxxxxxx> wrote:

but too minute to be noticed. If you put a trillion identical lines in the
main code you might notice it, but not if you did the same in a callback.

I don't believe this is correct, though I don't have any evidence (yet).
As I understand it it doesn't matter where the Javascript code is (callback
or not) it instead matters when that Javascript is given its turn on the
call stack. What DOES matter is when a callback, by way of a particular
APIs, makes use of C threading. It is then that Javascript (somehow)
relinquishes control to the C thread and is able to continue to the next in
the callback queue while still holding onto the callback pointer the C
thread will eventually call back to. This latter part is what I don't yet
have a firm grasp.

What is the relationship between the event loop of V8 in browsers versus
libuv in node?

An answer:
https://www.quora.com/What-provides-the-event-loop-in-node-js-v8-or-libuv

I have not yet researched what/how the browser does its event loop. To
date it's "just worked", but obviously once we get to the server-side it
becomes much more important.


Aaron Bartell
litmis.com - Services for open source on IBM i


On Tue, Oct 13, 2015 at 3:50 PM, Kevin Turner <kevin.turner@xxxxxxxxxxxxxxx>
wrote:

I think it depends on whether or not that line of code is in the main app
code or in a callback. If the former then I would say it is blocking - but
too minute to be noticed. If you put a trillion identical lines in the main
code you might notice it, but not if you did the same in a callback.

Sent from my iPad

On 13 Oct 2015, at 21:12, Aaron Bartell <aaronbartell@xxxxxxxxx> wrote:

So what you are saying is that the call to read the data queue is part
of
the DB2 adapter, and stays in the program stack until it completes rather
than dropping something on the "web api" stack.

Correct, and the way Node.js gets around that is through handing stuff
off
to C as a separate thread in the same process (aka IBM i job). This is
why
you'll see debates on the web about whether Node.js is single threaded or
multi threaded. In literal context Node.js is strictly single threaded
BUT
there can be additional threads in the same Node.js process if the
particular Node.js API (i.e. fs.readFile) implements C code under the
covers that creates a new/separate thread.

At least that's my understanding of it.

One thing I've been pondering but am not sure what audience to ask... I
do
believe everything in Javascript is blocking in nature. For example, the
below line of code blocks the Node.js thread until it is complete. The
thing is it completes really fast, so it doesn't often get put into the
category of "code that blocks". Instead only file system, networking,
and
database IO gets put into the "code that blocks" category because it
blocks
for long(er). Anybody know if that is a correct train of thought?

var x = 123;


Aaron Bartell
litmis.com - Services for open source on IBM i


On Tue, Oct 13, 2015 at 3:01 PM, Mark Murphy/STAR BASE Consulting Inc. <
mmurphy@xxxxxxxxxxxxxxx> wrote:

So what you are saying is that the call to read the data queue is part
of
the DB2 adapter, and stays in the program stack until it completes
rather
than dropping something on the "web api" stack. That makes more sense. I
like the animations, and the little tool behind this video. Makes it
easier
to understand what is going on.

Mark Murphy
STAR BASE Consulting, Inc.
mmurphy@xxxxxxxxxxxxxxx


-----Aaron Bartell <aaronbartell@xxxxxxxxx> wrote: -----
To: "Web Enabling the IBM i (AS/400 and iSeries)" <web400@xxxxxxxxxxxx>
From: Aaron Bartell <aaronbartell@xxxxxxxxx>
Date: 10/13/2015 03:28PM
Subject: Re: [WEB400] Why does node's Toolkit for i, use a database
connection to execute CL commands?

Awhile back I dug deep to learn about the Node.js/Javascript event
loop. I
found the following and I'd highly recommend watching it.
http://latentflip.com/loupe

The kicker that breaks a single Node process is when something is
blocking
in nature, and that can happen simply by writing a bit of Javascript
incorrectly (assuming the intention was to NOT block). Note, currently
the
DB2 adapter for Node.js is blocking. This more or less necessitates
multiple Node.js processes so you don't end up with a waiting line of
web
requests.
&#8203;

Aaron Bartell
litmis.com - Services for open source on IBM i


On Tue, Oct 13, 2015 at 2:06 PM, Mark Murphy/STAR BASE Consulting Inc. <
mmurphy@xxxxxxxxxxxxxxx> wrote:

I recognize this technique, but, due to my knowledge of node being
limited
at best, I have to wonder if this is an appropriate technique using
node.
That is, since Node is event driven, should there be a need to wait,
and
then loop around and check conditions again. RPG is not event driven,
hence
the need for such a loop. But I was under the impression that Node
already
incorporates this event loop and will call the appropriate function
when
the event occurs. I would expect to have to register to receive the
event
in some way, but not to have to code the event loop.

Mark Murphy
STAR BASE Consulting, Inc.
mmurphy@xxxxxxxxxxxxxxx


-----Kevin Turner <kevin.turner@xxxxxxxxxxxxxxx> wrote: -----
To: "Web Enabling the IBM i (AS/400 and iSeries)" <web400@xxxxxxxxxxxx

From: Kevin Turner <kevin.turner@xxxxxxxxxxxxxxx>
Date: 10/11/2015 04:44PM
Subject: Re: [WEB400] Why does node's Toolkit for i, use a database
connection to execute CL commands?

That's interesting stuff - thanks. I'm not entirely sure how to dig
deeper
but I will try :)

On 11 Oct 2015, at 17:47, Richard Schoen <
Richard.Schoen@xxxxxxxxxxxxxxx>
wrote:

I wonder if the loop is forcing a new job start each time on the i.

With XMLCGI, there is an IPC service that takes a few seconds each
time
it's re-initiated and I could see this being intensive if you had to
create
a new session for each interaction.

You can start the IPC session with a unique name and use the same job
over and over if I want to maintain state and use the same job on the I
which should improve performance I think.

Not sure how the node toolkit works, but this works good with .Net and
should be similar depending on how the toolkit was implemented.

Regards,

Richard Schoen | Director of Document Management Technologies,
HelpSystems
T: + 1 952-486-6802
RJS Software Systems | A Division of HelpSystems
richard.schoen@xxxxxxxxxxxxxxx
www.rjssoftware.com
Visit me on: Twitter | LinkedIn
----------------------------------------------------------------------

message: 1
date: Sat, 10 Oct 2015 22:32:23 +0000
from: Kevin Turner <kevin.turner@xxxxxxxxxxxxxxx>
subject: Re: [WEB400] Why does node's Toolkit for i, use a database
connection to execute CL commands?

It may or may not be of interest or relevant, but we have lots of code
that sits and waits of data on a keyed data queue. It waits for 5
seconds
then loops round and checks some stuff (like an instruction to end)
then
waits again.

When I did the same in a node app using itoolkit, the LPAR simply died
on its feet. It wasn't obvious why because the node app was not showing
up
as using much CPU. However it certainly was the culprit - I changed to
wait
for 60 seconds instead as it wasn't essential to loop every 5 secs. The
problem went away.

On 10 Oct 2015, at 15:58, Nathan Andelin <nandelin@xxxxxxxxx> wrote:


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