(mac obj args (w/uniq g `(let ,g (table) - ,@(map (fn ((k v)) `(= (,g ',k) ,v)) + ,@(map (fn ((k v)) `(sref ,g ,v ',k)) (pair args)) ,g)))
Avoid unnecessary use of atomic by obj
obj a lot in my code, using tables as objects/structs, and as I was condensing my code I began to get forms like:
(obj a (if foo (throw nil) ...) (obj a (readfile "foo"))
obj expands into a call to = to store the individual values in the new table, and arc2 protects expansions of = with atomic. The first form above generates an error since the throw can’t cross the continuation boundary created by atomic, and the second is dangerous since any delay inside of a call to atomic will cause all other uses of atomic to hang until it is done.
However, in the case of
obj there’s no need to protect the setting of the table values since the newly created table will not be visible to other threads at least until
obj returns. Thus the creation of the table can be done outside of the protection of atomic.
With this patch the first form now works:
arc> (catch (obj a (throw nil))) nil
And the second has no danger of hanging other threads.
By using git or patch, you can incorporate this patch into your version of Arc.
$ git pull git://github.com/CatDancer/arc.git tag arc2.obj-no-atomic0
$ mkdir arc $ cd arc $ git init $ git pull git://github.com/CatDancer/arc.git tag arc2.obj-no-atomic0
To apply this patch to your copy of arc using the patch command, download arc2.obj-no-atomic0.patch into your Arc directory, and at the Unix command line inside the Arc directory, type:
patch” is a standard utility that comes with Unix. (If you’re running Windows, iirc
patch comes with cygwin).
$ wget http://ycombinator.com/arc/arc2.tar [... downloading ...] $ tar xf arc2.tar $ cd arc2 $ patch <arc2.obj-no-atomic0.patch patching [...] $
The original Arc source is copyrighted by Paul Graham and Robert Morris and licensed under the Perl Foundations's Artistic License 2.0 as described in the “copyright” file in the Arc distribution.
My changes to Arc (this patch that I wrote) are in the public domain.
The combination of the original Arc and my changes together (what you get after you apply my patch) is also licensed under the Perl Foundations's Artistic License 2.0.