Marc Weber wrote:
Just to repeat what I said the last time someone brought this up: it is
impossible to support this in Ur/Web in the most general way, without
allowing for the possibility of some crazy behavior. The runtime system
feels free to restart program execution at any time, which wouldn't work
well with effectful commands that can't be undone.
Error triggers unlimited retry: Couldn't allocate new heap chunk contiguously
So it seems urweb tries with small heap and if everything fails it
retries with more?
That's right. The runtime system will also restart if an optimistic SQL
concurrency violation is detected, when certain errors are signaled, etc..
Currently, Ur/Web doesn't allow C FFI functions to return values in
algebraic datatypes besides those that can be represented with C enums.
However, you can easily provide the same set of operations (as
additional C FFI functions) on a new abstract type.
I think it would be cool if you could hardcode record types such as
result.blob
result.code
It would certainly be more convenient, but also less abstract, in some
sense. Because I don't think it would really make much difference, I
haven't implemented it.
http://gitorious.org/some-urweb-utility-libraries/uw-process
I'm surprised that the code you have leads compiled Ur/Web programs to
pass the GCC type checker. Your .urs file says that [Uw_process.exec]
returns a [Uw_process.result], which translates into the C type
'uw_Process_result'. However, your prototype for [Uw_process_exec]
gives the return type as 'uw_Process_result*', with an extra pointer
level. You should really define the type 'uw_Process_result' to be a
pointer type in the first place.
Right now I want to use it to outsource some jobs urweb can't do
natively yet.
I would instead recommend exposing application-specific C FFI functions
that exhibit appropriate transactional behavior. Exposing system()
directly is just a bad idea. It's obviously fine to use it internally
within transactional functions.
I'd love to add additional information such as "time out while waiting
for cmd sleep 2h" which will be very helpful. But you don't expose ctx using
the urweb.h file, do you? and the check function does not accept
additional strings as parameters.
I don't understand what you're trying to do.
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