[Lazarus] TAChart question

[José Mejuto]

On 10/1/2010 08:11, Michael Van Canneyt wrote:
> On Fri, 1 Oct 2010, Michael Schnell wrote:
>
>> On 10/01/2010 02:22 PM, Michael Van Canneyt wrote:
>>>
>>> ExtJS has no such mechanism to my knowledge, but I'm not a reference.
>>
>> last time I checked some months ago it was said to be a new feature,
>> but should work, even though I did not find anybody who has tested it.
>>
>>>
>>>> This is necessary to overcome the asymmetry of the http protocol.
>>>>
>>>> IMHO "Server-Events" are necessary to design a CGI program with some
>>>> complexity.
>>>
>>> Well, I create seriously complex applications. No such mechanism was
>>> necessary till now.
>>
>> Hmm, How to do notify the user that the server has finished complex
>> work in the background without blocking the interface and/or creating
>> excessive http polling traffic ?
>
> Define excessive polling ?
>
>> An easy to do (non complex) example for a good application for such a
>> method is a server that allows tow client to chat.
>>
>>>
>>>> Moreover "server-Internal-Events" like from Timers, serial or
>>>> "direct" TCP/IP communication, thread-notification, ... are very
>>>> desirable and should be able to fire "server-events" towards the
>>>> client.
>>>
>>> Why ? What could you possibly need to do that the server needs to
>>> contact
>>> the client ? Everything you need can be programmed in the client, in my
>>> experience.
>>
>> Above trivial example ("chat server")
>>
>> Real-world: Imagine an "embedded" program automatically working with
>> some hardware interfaces and/or serial and/or TCP/IP connections. Now
>> you want to provide it with a "web" interface that allows a "user" to
>> connect to it and do configuration and monitoring. For monitoring this
>> method is essential: many "states" in the program permanently change
>> due to the work of the program and the external situation. These state
>> changes need to be shown in the remote browser with low latency and
>> without excessive communication overhead.
>
> In my experience: keeping a connection open IS excessive communication
> overhead and very unreliable to boot.
>
> I thought like you, 12 years ago. Till reality kicked in. Faulty switches,
> company firewalls and whatnot. Not all servers/firewalls support HTTP 1.1
> (for a persistent connection) etc. Too many problems.
>
> So you end up with polling anyway. 10 polls per second is enough to fool
> the
> human eye and doesn't stress the server too much.
>
> Michael.

Aren't ExtJS Ajax calls asynchronous? The JavaScript code continues 
after firing a call to the server. There is a "callback" event that we 
can use when the server sent the reply back (and process success/failure 
events on the call).
At least I had to do some things to NOT give back the control to the 
user over the client side until the response arrives from the FPC server 
CGI/FCGI app (like disabling all controls for example).

IMO Exjs and FPC/Lazarus works superbly (you need FPC and Lazarus from 
the trunk SVN at the moment for it). You do not need ExtPascal at all.

AB