Issue #21309 has been updated by osyoyu (Daisuke Aritomo).
if we got some shareable mutable state, then we'd need a shareable mutex
Come to think of it, I now do think that `Mutex`es themselves are not the problem. So yes I agree with you, and am okay to close this ticket (I can come back when I find another use case).
For example on the Faraday case it would fail on `@default_options =` (on the `Faraday::Middleware` class).
Yes, and I feel that the usage of class variables in libraries are a big barrier for Ractor adoption. Too many gems in the wild and some in the standard library (openssl to name one) uses class variables to keep some "default" values or "cached" objects, which do not need be mutable for the entire process life.
For Timeout there is another semantics mismatch: if you use Ractors you shouldn't use Threads, otherwise you lose most benefits of using an actor model. So basically if you use Ractor you shouldn't use `Timeout`, even if Timeout wouldn't raise `Ractor::IsolationErrors`.
I am not sure about this. Sending HTTP request using net/http inside an Ractor should be a valid use case, and `Timeout` is blocking this (it is internally used to implement `open_timeout` `read_timeout` and `write_timeout`. ---------------------------------------- Feature #21309: Can Thread::Mutex be Ractor shareable? https://bugs.ruby-lang.org/issues/21309#change-112977 * Author: osyoyu (Daisuke Aritomo) * Status: Open ---------------------------------------- ## Background Keeping a `Mutex` object in a constant or a class instance variable is a common pattern seen in code with thread safety in mind. However, this kind of code does not play well with Ractors: ```ruby require 'thread' class C MUTEX = Mutex.new def self.foo MUTEX.synchronize { p 1 } end end Ractor.new { C.foo }.take ``` ``` t.rb:11: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues. #<Thread:0x000000011d80f368 run> terminated with exception (report_on_exception is true): t.rb:7:in 'C.foo': can not access non-shareable objects in constant C::MUTEX by non-main ractor. (Ractor::IsolationError) from t.rb:12:in 'block in <main>' <internal:ractor>:711:in 'Ractor#take': thrown by remote Ractor. (Ractor::RemoteError) from t.rb:13:in '<main>' t.rb:7:in 'C.foo': can not access non-shareable objects in constant C::MUTEX by non-main ractor. (Ractor::IsolationError) from t.rb:12:in 'block in <main>' ``` Many libraries follow this pattern. `Mutex` not being Ractor shareable is blocking these libraries from being used from inside Ractors. `Timeout` in stdlib in particular has large impact since it is required from many other gems by default, including `net/http`. https://github.com/ruby/timeout/blob/v0.4.3/lib/timeout.rb#L49-L50 https://github.com/lostisland/faraday/blob/v2.13.1/lib/faraday/middleware.rb... ## Proposal Make built-in concurrency primitives (Thread::Mutex, Thread::ConditionVariable and Thread::Queue) Ractor shareable. While this idea may not be strictly aligned with idea of the Ractor world (exchanging messages for controlling concurrency?), I have the feeling that too many code is blocked from running in Ractors because `Mutex` is not Ractor shareable. Allowing `Mutex`es to be shared would make a large portion of existing Ruby code Ractor-compatible, or at least make migration much easier. I believe that it won't be semantically incorrect, since they are concurrency primitives after all. One thing to consider that the current `Mutex` implementation is based on the GVL (I believe so). Migration to some other implementation e.g. pthread_mutex or CRITICAL_SECTION may be needed to make Mutex work well on Ractors. -- https://bugs.ruby-lang.org/