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Feature #14819

open

Efficient cstring to RVALUE typecasting for c extension gems

Added by sam.saffron (Sam Saffron) about 3 years ago. Updated about 3 years ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:87368]

Description

A general pattern I notice in the PG / MySQL and other gems is a general need for a C string to RVALUE type casting.

A lot of the problem is that the libpq likes returning strings and you do not want to allocate an extra RVALUE string for an IP address or Date and so on when returning data for the data set.

The result is that many c extension gems carry around very similar code for casting C strings to dates/ip addresses and so on.

An example of such a function is: https://github.com/ged/ruby-pg/blob/master/ext/pg_text_decoder.c#L551-L715

Ruby already provides quite a few helpers such as rb_cstr2inum I wonder if there are some gaps we can fill like

rb_cstr2ipaddr rb_cstr2time rb_cstr2date rb_cstr2macaddr

Having these implementation could help reduce code carried in gems and offer a faster method for adoption of faster patterns. For the interim gems could copy and paste MRI implementation and longer term just add an #if to lean on MRI.

An alternative "wild" idea here would be to allow Ruby code to operate in an "unsafe" way on strings that are not RVALUES yet, .NET has a similar mechanism with unsafe. Eg:

unsafe do
  non_rvalue_string = api.getcstr
  # operate on string with a limited set of operators that only allocate on stack
  api.free non_rvalue_string
end

If the wild idea here is interesting perhaps lets open a new topic, for this purpose let's discuss rb_cstr2ipaddr rb_cstr2time rb_cstr2date rb_cstr2macaddr

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