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From "John Dougrez-Lewis" <jle...@lightblue.com>
Subject RE: THRIFT-66 - Bidirectional communication
Date Tue, 21 May 2019 05:22:23 GMT
Indeed, you could just skip the intermediate IDL generation and go straight to the language-specific
code generation.

The IDL to IDL just serves as a mechanism to localise the necessary changes, keeping the existing
language-specific code generation code as it is, so only the extra plumbing language-specific
code needs to written.


-----Original Message-----
From: Jens Geyer [mailto:jensg@apache.org] 
Sent: 20 May 2019 21:53
To: dev@thrift.apache.org
Subject: Re: THRIFT-66 - Bidirectional communication

Hi,

Sorry, I can't follow. IDL generates language specific code already.

Get me right: Having another IDL to create an IDL to create code from is not a bad idea in
general (I have done that myself), but I can't see the added value in the context of Thrift.
I only see things getting way more complicated as necessary.

Why can't we model what we want with the great, simple and "to the point" 
IDL we have aleady, maybe expand it a bit where suche becomes necessary?

Have fun,
JensG



-----Ursprüngliche Nachricht-----
From: John Dougrez-Lewis
Sent: Monday, May 20, 2019 7:26 AM
To: dev@thrift.apache.org
Subject: RE: THRIFT-66 - Bidirectional communication

> And the benefit would be ... ?

The ability to extend functionality across all languages in a consistent way using the existing
implementation.

The only additional language-specific code that would need to be added would be to plumb-in
and glue together the two channels.


-----Original Message-----
From: Jens Geyer [mailto:jensgeyer@hotmail.com]
Sent: 19 May 2019 21:01
To: dev@thrift.apache.org
Subject: Re: THRIFT-66 - Bidirectional communication

> > > async was already a keyword long ago. It's now called "oneway".
> But 'oneway' provides no guaranteed deterministic mechanism of
> indicating back to the client any

I didn't say that. I just said that async already was used as a keyword.


> >  What exactly would that preprocessor do? Generate IDL from IDL?
> Yes.

And the benefit would be ... ?



-----Ursprüngliche Nachricht-----
From: John Dougrez-Lewis
Sent: Saturday, May 18, 2019 8:39 AM
To: dev@thrift.apache.org
Subject: RE: THRIFT-66 - Bidirectional communication

Hi,

> At least PUB/SUB can be implemented solely on the transport level. No
> IDL change necessary.

My understanding is that Thrift generally provides only synchronous RPC, 
making with one synchronous return. How would multiple subsequent 
Subscription updates be sent back to the Client?


> async was already a keyword long ago. It's now called "oneway".

But 'oneway' provides no guaranteed deterministic mechanism of indicating 
back to the client any subsequent processing failures of the call on the 
server side, so it appears very fragile and so would be difficult to justify 
it being used in any serious professional applications such as Financial 
Trading Systems.


> Not sure if I can follow. What exactly would that preprocessor do?
> Generate IDL from IDL?

Yes.


>> [in/out/inout] parameter

> There was some discussion about this a while ago, don't remember the
> ticket.
> Technically that should be possible, since the data are transferred in
> a struct anyway, so multiple out parameters (or even in/out) should
> really not be that hard to implement.

Yes, even with just a synchronous IDL extension, out parameters can be 
always be rewritten as members of a struct in the returned values type.


------------------

In addition, Callback methods could be passed as arguments in the A<=>B
extended IDL and translated into interface methods on the B=>A async
response path, e.g.


A<=>B IDL:

[aync] methodReturnType Method(arg1, arg2, callbackType Arg)

// define callbackType signature

cbReturnType callbackType(cbArgtype1, cbArgtype2)

=======>

generates:

A=>B IDL

// immediate return to provide handle for context for subsequent async
return
// requires caller to supply callbackHandle to provide context for callback

handleType Method(arg1, arg2, callbackHandle)

B=>A IDL

// async return from method call
void Method(handleType, methodReturnType)

// call for async callback
cbReturnType CallbackType(handleType, callbackHandle, cbArgtype1,
cbArgtype2)


-----------------

Regards,

John


-----Original Message-----
From: Jens Geyer [mailto:jensg@apache.org]
Sent: 17 May 2019 23:36
To: dev@thrift.apache.org
Subject: Re: THRIFT-66 - Bidirectional communication

Hi,

> That gets you to the point where Thrift supports and generates
> bidirectional, async & pub/sub based on IDL

At least PUB/SUB can be implemented solely on the transport level. No IDL
change necessary.


> adding attributes [asyc] method/interface

async was already a keyword long ago. It's now called "oneway".


>  pre-processing the extended IDL with a new pre-processor to generate the
> representations of the service definitions for both sides in terms of the
> current IDL

Not sure if I can follow. What exactly would that preprocessor do? Generate
IDL from IDL?

As a general statement, I would recommend to strictly separate between an
interface contract (which the IDL is and should be) and a concrete
implementation or  configuration setup (which the IDL should not be).


> [in/out/inout] parameter

There was some discussion about this a while ago, don't remember the ticket.
Technically that should be possible, since the data are transferred in a
struct anyway, so multiple out parameters (or even in/out) should really not
be that hard to implement. I have no idea if we run into subtle problems
with certain languages and how that could be circumvented (by using structs
maybe) and if in/out is really supported by all of them on a language level,
we will find out.


Have fun,
JensG


-----Ursprüngliche Nachricht----- 
From: John Dougrez-Lewis
Sent: Thursday, May 16, 2019 6:29 AM
To: 'James E. King III'
Cc: dev@thrift.apache.org
Subject: RE: THRIFT-66 - Bidirectional communication

Yes, my suggestion is for an enhancement to Thrift to make it bidirectional,
as follows:


1) use 2 connections, A => B, and B => A using what is already in place.

2) write, by hand, a new, supporting choreography code to establish this
double connection, in the first instance for a single language

3) extend the IDL support this - adding attributes [asyc] method/interface,
[pub/sub] method/interface, [in/out/inout] parameter

4) extend the IDL generation to implement this:

      i) pre-processing the extended IDL with a new pre-processor to
generate the representations of the service definitions for both sides in
terms of the current IDL

      ii) generate the language dependent code required to hook up at of the
two ends.

5) implement across multiple languages


That gets you to the point where Thrift supports and generates
bidirectional, async & pub/sub based on IDL

Then, optionally:

6) Having achieved a working implementation defined by an extended IDL,
consider re-implementing in terms of a single bidirectional transport rather
than 2 existing unidirectional independent transports.


The extended IDL defining a single async/pubsub A<=>B interface is used to
generate 2 interfaces: an outgoing A=>B and an async response return channel
B=>A, e.g.:


A<=>B
  [async] returntype functionName (arg1, arg2)
=>
A=>B
  Handletype functionName (arg1, arg2)
B=>A
  void functionName (Handletype, returntype)

A<=>B
  [async] returntype functionName (arg1, arg2, [out] arg3)
=>
A=>B
  Handletype functionName (arg1, arg2)
B=>A
  void functionName (Handletype, returntype, arg3)


A<=>B
  [async] returntype functionName (arg1, arg2, [inout] arg3)
=>
A=>B
  Handletype functionName (arg1, arg2, arg3in)
B=>A
  void functionName (Handletype, returntype, arg3out)



-----Original Message-----
From: James E. King III [mailto:jking@apache.org]
Sent: 15 May 2019 19:02
To: jlewis@lightblue.com
Cc: James E. King III; dev@thrift.apache.org
Subject: Re: THRIFT-66 - Bidirectional communication

Re: Visio - There are no "endpoint" implementations that allow for
bi-directional communication over a single transport connection today.
Is that the Visio you were referring to?  The only implementation of that
concept is buried in the THRIFT-66 attachments, and only for C#, and it was
done on a codebase about 8 years past...

With today's thrift code if you want either end to be a client (make
requests) or a server (reply to requests) you would need to separately
instantiate a client or server on each end and have them connect to
each-other, i.e.

A ---> B (A sends requests to a thrift server on B, B replies, on a
transport) A <--- B (B sends requests to a thrift server on A, A replies, on
a transport separate from the last one)

It sounds like what you'd like to get to is:

A <--> B (A and B can function as a client or as a server over the same
transport)

Thrift cannot do the latter today, so I would recommend the former, using
one transport for each direction.

Given they will both be on the same system, if your languages support it,
unix domain sockets are quite fast.
Otherwise if you want a shared memory solution you need to write your own
transport for that.

- Jim

On Wed, May 15, 2019 at 1:12 PM John Dougrez-Lewis <jlewis@lightblue.com>
wrote:
>
> Hi Jim,
>
> The "oneway" route looks a bit fragile in the face of failures in the
> subsequent server-side processing which then cannot be signalled back to
> the client.
>
> The 2-way connection would be the way forward for me, particularly since
> it would work with across multiple languages.
>
> My primary use case would be a simple language bridge mechanism for a
> library to allow processes coded in one language to call, with potentially
> asynchronously returns, and pub/sub, to another process hosting a library
> coded in another language running (in the first instance) on the same box,
> communicating via IPC, preferably fast shared memory, but failing that
> sockets would do.
>
> You put a Visio diagram up back in 2010. Is the underlying source code for
> that available now ?
>
> Rather than hand-rolling the 2-way connection setup/teardown and
> supporting code, for each and every language each time, it would be nice
> if Framework code for that could be generated automatically from an
> enhanced and extended version of the IDL.
>
> Regards,
>
> John
>
> -----Original Message-----
> From: James E. King III [mailto:jking@apache.org]
> Sent: 15 May 2019 12:05
> To: dev@thrift.apache.org; jlewis@lightblue.com
> Subject: Re: THRIFT-66 - Bidirectional communication
>
> Hello!
>
> Thrift is still a dedicated client/server model environment where clients
> can request and servers reply.  The easiest way to make it 2-way today is
> to open a connection both ways.  If you don't have firewalls in the way
> then you can do this effectively.  The more difficult and more correct way
> to do it would be to rewrite the transport layer to use endpoints in which
> each side can be a client and/or server for any number of services (using
> TMultiplexedProtocol on top of another protocol, like TBinaryProtocol).
> This design allows one end to be a "listener", one end to be an
> "initiator" (starts the connection), and after they connect they are equal
> peers with the ability to request or reply of each-other.
>
> You can approximate asynchronous behavior by exclusively using "oneway"
> requests in your design.  I'd suggest avoiding use of oneway requests with
> THttpProtocol varieties however as today there are some issues, since Http
> transport requires a response to be sent, and "oneway" dictates there is
> no reply, and most languages do not handle it well right now (there are
> open backlog issues for this).
>
> For a matrix of supported languages, protocols, transports, and server
> types, see the file LANGUAGES.md at the root of the github repository.
>
> Another idea I was toying with a while ago was to add a message bus
> transport to Thrift which would allow for things like reliable delivery
> and broadcast semantics but that also does not exist today.
>
> - Jim
>
> On Wed, May 15, 2019 at 1:05 AM John Dougrez-Lewis <jlewis@lightblue.com>
> wrote:
> >
> > Hi,
> >
> >
> >
> > I was looking for a mechanism to be able to provide
> > language-agnostic API support to a hobby project I've been working on
> > for some time.
> >
> >
> >
> > By following a trail of papers, books and references, I eventually
> > came across Apache Thrift and have found and started going through
> > Randy Abernethy's new book.
> >
> >
> >
> >
> >
> > Essentially what I was looking for was support for asynchronous
> > calls, and by extension, pub/sub and two way communication across
> > and between multiple languages over some channel, preferably IPC but in
> > the worst case sockets.
> >
> >
> >
> >
> >
> > Having read the book, I can see that there is support for basic
> > synchronous RPC between a client and a server over a significant
> > number of languages and for just a very few languages, such as java,
> > some element of support for asynchronous callbacks, and otherwise
> > one-way methods that do not provide indication of subsequent failure.
> >
> >
> >
> > It appeared to me one way of extending bi-directional asynchronous
> > support would be to have the client to set itself up as a server for
> > the server at the other end to connect to, and then it would just be
> > a question of choreographing the setting up of a pair of RPC channels.
> >
> >
> >
> > An asynchronous call could be implemented by providing a synchronous
> > method that simply immediately returns a handle to the caller, and
> > the server would then continue to process the call request on a
> > background threadpool thread on the server, and the async result
> > would then be signalled by a call from the server back to the client
> > on the 2nd channel with the handle providing a context to lookup the
> > result.
> >
> >
> >
> > Pub/sub would just then be multiple calls from the server back to
> > the client.
> >
> >
> >
> > The whole thing could sit on top of the existing unidirectional RPC
> > implementation and provide full asynchronous calls & pub/sub across
> > *ALL* supported languages at probably very little additional effort,
> > with no changes to the existing code.
> >
> >
> >
> > You could then have a framework that extended the existing IDL to
> > include decoration with attributes for async & pub/sub methods & in/out
> > parameters.
> >
> >
> >
> > This extended IDL could then be pre-processed to generate
> > client-server and server-client service definitions in the existing
> > base IDL language, together with generating supporting glue code to
> > compile to provide the support for hooking up the channels between each
> > side.
> >
> >
> >
> > I note that THRIFT-66 was raised 10 years ago, but it looks like the
> > C# code was never made available for release by Dell.
> >
> >
> >
> > I have some questions:
> >
> >
> >
> > 1)      What is the current state of plans for this supporting this sort
> > of
> > functionality? What issues have been encountered ?
> >
> >
> >
> > 2)      Is there a document/spreadsheet somewhere showing a matrix of
> > what
> > Transports and Protocols are supported for each language?
> >
> >
> >
> >
> >
> > Regards,
> >
> >
> >
> > John
> >
> >
> >
> >
> >
> >
> >
>





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