[ruby-core:72619] [Ruby trunk - Misc #11904] Why was Thread.exclusive deprecated?

Issue #11904 has been updated by Benoit Daloze.


Tony Arcieri wrote:
> Is a single-threaded require actually a *guarantee* of every Ruby VM?

Not single-threaded, but each file should be loaded at most once.
Single require per file/path is certainly highly desirable,
otherwise you may load the same file twice.
It's also a lot easier to make it thread-safe than autoload IMHO.

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Misc #11904: Why was Thread.exclusive deprecated?
https://bugs.ruby-lang.org/issues/11904#change-55876

* Author: Tony Arcieri
* Status: Rejected
* Priority: Normal
* Assignee: 
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See: https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/52554

Why was Thread.exclusive deprecated? It is useful for when you're uncertain about whether the caller is multithreaded or not, and therefore cannot initialize a mutex because the mutex must be initialized in a thread-safe context where it's not possible for multiple caller threads to initialize the mutex concurrently.

One use case is here: this is an idempotent native function invoked via FFI. The contract is that it can be called repeatedly, but only by one thread at a time (concurrent calls from multiple threads can potentially corrupt its internal state):

https://github.com/cryptosphere/rbnacl/blob/master/lib/rbnacl.rb#L88

Thread.exclusive is useful because it provides an implicit mutex you can ensure is initialized correctly before any other threads start.



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