2020-07-11 21:25 GMT, Larry Garfield <la...@garfieldtech.com>: > On Sat, Jul 11, 2020, at 4:04 PM, Olle Härstedt wrote: > >> > I think that would do a far better job of addressing the >> > shared-mutable-state issue than reference counting, because it attacks >> > the >> > root problem rather than a symptom. >> > >> > --Larry Garfield >> > >> > -- >> > PHP Internals - PHP Runtime Development Mailing List >> > To unsubscribe, visit: https://www.php.net/unsub.php >> >> I think freezing objects might be better fit for my imagined use-case. >> The only problem I see is that you can't really unfreeze them. Imagine >> a database connection that only can be open/closed at refcount = 1: >> >> ``` >> $connection = new OwnershipConnection(); >> $connection->open(); >> $ps = new PostService($connection); >> $ps->updateAllPosts(); // Throws exception if $connection->close() >> $connection->close(); >> ``` >> >> With freeze, you could also do >> >> ``` >> $ps = new PostService($connection->freeze()); >> ``` >> >> to ensure it's not closed by mistake. But then you couldn't close the >> connection at all, except in __destruct. >> >> Especially, CoW for objects (at opt-in) is not a replacement where >> ownership is supposed to replace immutability for performance reason, >> e.g. creating a separate immutable database connection for every class >> that uses it. >> >> Immutable builder are already part of PSR, e.g. here: >> https://www.php-fig.org/psr/psr-7/ >> >> I have to wonder how reasonable this is, when freezing or ownership >> are also relevant solutions, with different trade-offs. >> >> Olle > > A database connection is the textbook example of an object that *should* be > shared; giving a separate connection to every service object is only going > to waste time opening multiple connections and waste open connections. > Please don't do that. > > Your example seems directly contrary to the goal you're describing. > > --Larry Garfield > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: https://www.php.net/unsub.php > >
You're misunderstanding. :) Yes, it should be shared, but not with the same access level as the owner. If a dependent class closes the connection it will cause spooky-action-at-a-distance somewhere else in the program. Sorry, it's related to refcount as ownership checking and not to throwing exception at refcount > 1. More like, "limit access at refcount > 1" (at borrow, that is). Reference counting can be used for both poor man's ownership semantics and to enforce non-aliasing. So yeah, maybe I should just suggest that something like this extension gets merged into vanilla PHP: https://github.com/qix/php_refcount (proper way to get refcount instead of a zval dump). Or maybe make zval dump return something instead of dumping a string. Olle -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: https://www.php.net/unsub.php
