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It seems to me that the Ruby community has been freaking out a little about autoload since this famous thread, discouraging its use for thread safety reasons.
Does anyone know if this is no longer an issue in Ruby 1.9.1 or 1.9.2? I've seen a bit of talk about wrapping requires in mutexes and such, but the 1.9 changelogs (or at least as much as I've been able to find) don't seem to address this particular question. I'd like to know if I can reasonably start autoloading in 1.9-only libraries without any reasonable grief.
Thanks in advance for any insights.
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None of the core data structures (except for Queue) in Ruby are thread-safe. The structures are mutable, and when shared between threads, there are no guarantees the threads won't overwrite each others' changes. Fortunately, this is rarely the case in Rails apps.
No, you cannot rely on Hashes being thread safe, because they aren't built to be thread safe, most probably for performance reasons. In order to overcome these limitations of the standard library, Gems have been created which provide thread safe (thread_safe) or immutable (hamster) data structures.
Bringing a 2011 update to this, since I was curious about it too.
Two tickets are currently opened:
The core devs suggest that require and autoload work in the same manner and are thread safe, in CRuby/JRuby 1.9. This, in the sense that ruby keeps a lock until the file is fully loaded.
This has the inconvenient side-effect of introducing potential deadlocks, however. Specifically:
The conclusion probably is: require everything you need before starting a thread if there's any potential for deadlock in your app.
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