Issue #21309 has been reported by osyoyu (Daisuke Aritomo). ---------------------------------------- Feature #21309: Can Thread::Mutex be Ractor shareable? https://bugs.ruby-lang.org/issues/21309 * 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/