[fpc-pascal] Improved FPC JSON-RPC support

[Michael Van Canneyt]

On Tue, 28 Dec 2021, Don Duvall via fpc-pascal wrote:

> Has any performance tests been ran, to see what the runtime impact of 
> utilizing RTTI is? Hopefully negligent in the grand scheme...

No tests have been run. 
I also don't know what exactly you would compare it with ?

Using some plain common sense:
The 'older' json-rpc mechanism relied on TJSONRPCHandler components on a Datamodule.
Loading a datamodule and all components (one per exposed method) on it also
uses RTTI, but is bound to beslower due to all the loading & parsing 
of the lfm file for every call.

Even so, all that will be dwarfed by the network latency & http+json  protocol:

Many years ago, I did a speed comparison test of the various protocols
offered by Remobjects SDK in delphi. It was published in Toolbox magazine:

https://www.freepascal.org/~michael/articles/index.html#remobjects2 
(the date on the article is misleading, it is actually older, must have been
2005 or so)

They showed clearly that the used protocol (http & xml) is the largest factor.
in 2013 I did many tests in a JSON REST framework: the times for streaming 
were dwarfed by the time spent on network & database access.

Translated to RPC: if you want speed, don't use HTTP or JSON. WST offers a
binary protocol and plain TCP channel, it's bound to be much faster.

Michael.

>
> Thanks,
> Don
>
> On 12/28/2021 2:11 PM, Michael Van Canneyt via fpc-pascal wrote:
>>
>>
>> On Tue, 28 Dec 2021, Graeme Geldenhuys via fpc-pascal wrote:
>>
>>> On 2021-12-28 15:25, Michael Van Canneyt via fpc-pascal wrote:
>>>>
>>>> Thanks to the magic of RTTI and Invoke(), creating a JSON-RPC server 
>>>> has
>>>> just become significantly easier !
>>>
>>> That's pretty neat - nicely done Michael.
>>
>> We do our best.
>>
>>>> // Create a class that implements the interface
>>>> Type
>>>>    TIntf2Impl = class(TInterfacedObject, IMyOtherInterface)
>>>>    public
>>>>      function Echo(args: TStringArray): String;
>>>>      function SayHello: string;
>>>>    end;
>>>
>>> ...snip...
>>>
>>>> // Register the class using an interface factory:
>>>> Function GetMyOtherInterface(Const aName : string) : IInterface;
>>>> begin
>>>>    Result:=TIntf2Impl.Create as IInterface;
>>>> end;
>>>
>>>
>>> Slightly off topic, and my Object Pascal is getting a bit rusty as 
>>> the years go by. <grin> ;-) In your factory above, is the "as 
>>> IInterface" part needed. Can't the FPC compiler automatically cast 
>>> the return type based on the function return type, and the fact that 
>>> the compiler should know that TIntf2Impl type implements 
>>> TInterfacedObject?
>>
>> No, theoretically it probably could, but type inference is not 
>> implemented in Pascal.
>>
>> Michael.
>>
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