Q: How can server callback the client's function?

[林晓锋]

Hi ,all:

    It's memtioned that "Make a request that will call back to a function defined locally." at calculator-client.c++.I'm confused how and where the server holds the function and when to call it. (I guess that it's in the EventLoop::turn() by reading code ,but i'm not sure how it works) 

[Kenton Varda]

Hi,

Sorry, I don't really understand the question. The client calls `evaluate()` and passes a `Expression` of type `call` containing a `Function` capability. The server receives this expression, calls `getCall().getFunction()` to receive a `Function::Client`, which it can then use to invoke `Function.call()`.

-Kenton

On Mon, Oct 28, 2019 at 5:41 AM 林晓锋 <lxf4...@gmail.com> wrote:

Hi ,all:

    It's memtioned that "Make a request that will call back to a function defined locally." at calculator-client.c++.I'm confused how and where the server holds the function and when to call it. (I guess that it's in the EventLoop::turn() by reading code ,but i'm not sure how it works) 

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[林晓锋]

Hi, 

    Thanks for your response!

    For me, I want to keep the `function` which was sent by the client, so that the server can call it whenever it wants. But it seems that the `function` is called immediately by sever when it is received. And I don't know how I can get the `function`'s name and params list, which may be useful when the server wants to call the `function` with its own params.

在 2019年10月29日星期二 UTC+8上午1:13:08，Kenton Varda写道：

Hi,

Sorry, I don't really understand the question. The client calls `evaluate()` and passes a `Expression` of type `call` containing a `Function` capability. The server receives this expression, calls `getCall().getFunction()` to receive a `Function::Client`, which it can then use to invoke `Function.call()`.

-Kenton

On Mon, Oct 28, 2019 at 5:41 AM 林晓锋 <lxf4...@gmail.com> wrote:

Hi ,all:

    It's memtioned that "Make a request that will call back to a function defined locally." at calculator-client.c++.I'm confused how and where the server holds the function and when to call it. (I guess that it's in the EventLoop::turn() by reading code ,but i'm not sure how it works) 

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[Kenton Varda]

On Mon, Oct 28, 2019 at 6:50 PM 林晓锋 <lxf4...@gmail.com> wrote:

Hi, 

    Thanks for your response!

    For me, I want to keep the `function` which was sent by the client, so that the server can call it whenever it wants. But it seems that the `function` is called immediately by sever when it is received.

You can keep a `Client` as long as you want. The calculator example server sends an RPC to the `Function::Client` immediately, but there's nothing stopping a server from hanging onto this value long-term.

And I don't know how I can get the `function`'s name and params list, which may be useful when the server wants to call the `function` with its own params.

Hmm, I think maybe the specific example here might be causing some confusing. The type `Function` is an interface defined in calculator.capnp -- it is specific to this example case. You can send any interface type over RPC, not just `Function`. You can of course include with it any metadata you want, by encoding the metadata in the Cap'n Proto message.

-Kenton

 

在 2019年10月29日星期二 UTC+8上午1:13:08，Kenton Varda写道：

Hi,

Sorry, I don't really understand the question. The client calls `evaluate()` and passes a `Expression` of type `call` containing a `Function` capability. The server receives this expression, calls `getCall().getFunction()` to receive a `Function::Client`, which it can then use to invoke `Function.call()`.

-Kenton

On Mon, Oct 28, 2019 at 5:41 AM 林晓锋 <lxf4...@gmail.com> wrote:

Hi ,all:

    It's memtioned that "Make a request that will call back to a function defined locally." at calculator-client.c++.I'm confused how and where the server holds the function and when to call it. (I guess that it's in the EventLoop::turn() by reading code ,but i'm not sure how it works) 

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