[Swift-user] Question about programs, wrappers and exceptions

[Michael Wilde]

> From: "Lorenzo Pesce" <lpesce at uchicago.edu>
> 
> My current issue has to deal with returning return values from
> programs, contained into wrappers and to a degree how to
> transparently manage exceptions and return values within swift.

Programs (i.e., app() functions) can only return files.

If you want to return values (eg a set of scalars) from an app() back into the calling Swift script, your app should place them into a file, and you can then use readData() or readData2() to read these values into Swift scalars, arrays, or structures.

The best way to do this is to define a wrapping function written in Swift to do the readData() and make it transparent to higher-level callers.

Regarding errors and exceptions: Swift does not have an exception facility.  An app() is considered by the Swift runtime to have failed when it returns a non-zero exit code. When it does so, Swift considers the app() call to have failed and will then apply the retry and recovery logic specific by the properties execution.retries and lazy.errors.  Swift will also consider the app to have failed if the files that it expects the app to create (per its parameters and their mappings) do not exist.

> I would also to understand in more details about the mechanics of
> coasters. It is not entirely clear to me how sometimes they seem to
> relinquish control of nodes even when not all the calculations are
> completed. It seems like a new batch of jobs is submitted as a new
> calculation even when it is not strictly necessary (or doesn't seem
> to be).

A coaster worker will exit when no ready app() jobs submitted by the Swift script will fit into the remaining wall time of the worker.  Could that be happening in the cases of this you have seen?

- Mike