Moving a function into a different `place?`

[David Storrs]

What is the best way to pass a function into a child `place`?

I've got a server function that accepts a dispatch function as one of its arguments and I need to be able to run the server in a separate `place` (in the dynamic-place sense) because it's part of a GUI application. [details]

My initial thought was to start the place and then use place-channel-(put/get) to move the run-time argument from the main place over into the child.  I immediately realized that doesn't work because functions are not `place-message-allowed?` values.  Next I thought about using a parameter, but parameters in a child place are set to their *initial* values, not their run-time values.  (Barring a few special cases.)

I considered passing a string or symbol list and then eval'ing it in the child place.  I immediately rejected this idea and told my brain that it was being bad and it got no cookies.

At this point my only remaining idea is to place-channel-(put/get) a module name that can be dynamic-required in the child place in order to get the dispatch function.  Is there a better way?

[details]

The Racket GUI library has an issue where e.g. launching an 'Open File' dialog will freeze all of Racket until the user closes the dialog.  This can cause the server to time out.  Since it's all of Racket that's being frozen and not just the current thread it's necessary to put the server code into an entirely different `place`.

[Sam Tobin-Hochstadt]

Your "only remaining idea" is what I'd recommend for telling another
place what function to run (that's how dynamic-place works in the
first place). But your [details] sounds worrying. I just tested on my
machine and it didn't happen for me, and I don't think it's supposed
to happen on other platforms either.

Sam

> --
> You received this message because you are subscribed to the Google Groups "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to racket-users...@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAE8gKoemyTeoP2GW5-_h6rGxW_1YcfyCQfHSs9ee98h3pRE4mg%40mail.gmail.com.

[David Storrs]

On Thu, Jul 1, 2021 at 2:42 PM Sam Tobin-Hochstadt <sa...@cs.indiana.edu> wrote:

Your "only remaining idea" is what I'd recommend for telling another
place what function to run (that's how dynamic-place works in the
first place). But your [details] sounds worrying. I just tested on my
machine and it didn't happen for me, and I don't think it's supposed
to happen on other platforms either.

*frowns*

*goes and checks*

My mistake, I misremembered the details.  It only happens if you want the platform-specific version of the dialog.  If you use the Racket version it's fine but then your interface doesn't match what the user is expecting.

https://groups.google.com/g/racket-users/c/wexYxYYU7GE/m/3zXxn6NoAwAJ?pli=1

[Sam Tobin-Hochstadt]

Ah, this must be a case where different platforms behave differently,
because I still see other threads running even with
`finder:std-get-file` on Linux.

Sam

> To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAE8gKoemg5DpdSx-iGcmu-5huM19zCtrdZXkjHHE2JhK7aGpXg%40mail.gmail.com.

[George Neuner]

On 7/1/2021 2:36 PM, David Storrs wrote:
> What is the best way to pass a function into a child `place`?

1.  just define the functions in a context the place can see
2.  send the name of a local file for the recipient to dynamic-require
3.  send the definition file for the recipient to save locally and
dynamic-require
4.  define the function(s) with serial-lambda and serialize / deserialize

> I've got a server function that accepts a dispatch function as one of
> its arguments and I need to be able to run the server in a separate
> `place` (in the dynamic-place sense) because it's part of a GUI
> application. [details]

Not a problem if using /dynamic/  (thread in same process) places.
See
   https://docs.racket-lang.org/reference/places.html
https://docs.racket-lang.org/reference/places.html?q=place#%28part._places-syntax%29

> I considered passing a string or symbol list and then eval'ing it in
> the child place.  I immediately rejected this idea and told my brain
> that it was being bad and it got no cookies.

You /can/ do that ... but you don't ever have to stoop to eval.

> At this point my only remaining idea is to place-channel-(put/get) a
> module name that can be dynamic-required in the child place in order
> to get the dispatch function.  Is there a better way?

Depends on whether you're using /dynamic/ (same process) or
/distributed/ (separate process) places.

With dynamic places you can (often) just provide the code for the place
to execute.  For complicated things you may have to use
serial-lambda/serialize/deserialize, but often you can simply provide
the necessary functions in context.

> [details]
> The Racket GUI library has an issue where e.g. launching an 'Open
> File' dialog will freeze all of Racket until the user closes the
> dialog.  This can cause the server to time out. Since it's all of
> Racket that's being frozen and not just the current thread it's
> necessary to put the server code into an entirely different `place`.

And invalidating any part of the visible window does the same thing
until the window is redrawn.


George