Localizing Variables in Coroutines

While I was browsing the CPAN the other day, I came across Coro::LocalScalar and I said to myself, oh, what a useful idea… it lets you localize globals to a thread. An important feature if you do anything in your thread with those pesky globals from perlvar, for instance.

But, said I, its calling convention is the rather gross Coro::LocalScalar->new->localize($scalar); and it’s implemented using tie and only for scalar values. It would be nice to have a new keyword and support for arrays and hashes as well. As it happens, I’d also recently run across Begin::Declare, which is a Devel::Declare based module that provides custom variable declarations.

A few hours later, with the example of Begin::Declare to work from, I bring you Coro::Localize (now on a CPAN mirror near you). It’s localization is achieved through a combination of Coro’s on_enter /on_leave blocks and Data::Alias.

So you might use it this way:

our $scalar = "some value";

async {
    corolocal $scalar = "thread local";
    ...
};

$scalar will be set to "thread local" for all of the code inside the async block, even if you cede and someone else fiddles with the variable. Similarly, any code outside the async block will only ever see "some value".

Leave a comment

About Rebecca

user-pic I've been happily playing in Perl's playground since 1997, when I decided I really wanted to work with Unix and the Web, rather then DOS, where my previous work had been. Lately, my rate of publishing has code has increased a lot, in large part thanks to Github.