Issue #20288 has been reported by ioquatix (Samuel Williams). ---------------------------------------- Bug #20288: `rb_fiber_scheduler_close` exceptions are not handled in `rb_fiber_scheduler_set`. https://bugs.ruby-lang.org/issues/20288 * Author: ioquatix (Samuel Williams) * Status: Open * Priority: Normal * Assignee: ioquatix (Samuel Williams) * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- The code responsible for setting a new scheduler on a thread does not properly handle exceptions raised by `rb_fiber_scheduler_close`. If `rb_fiber_scheduler_close` raised an exception, the assignment `thread->scheduler = scheduler` would not be executed. This leaves the thread in an undefined state because it might still hold a reference to the old scheduler, which was supposed to be closed and replaced. ## Steps to Reproduce: 1. Define a custom fiber scheduler that raises an exception in its close method. 2. Set the custom scheduler on a thread. 3. Attempt to replace the custom scheduler with a different scheduler. 4. Observe that if the close method of the original scheduler raises an exception, the thread's scheduler reference is not updated. ## Proposed Fix: The use of `rb_ensure` can be introduced to wrap the call to `rb_fiber_scheduler_close` to ensure that, regardless of whether an exception is raised, `thread->scheduler` is set to `Qnil`, and then `thread->scheduler = scheduler` is safely executed to update the thread's scheduler reference. -- https://bugs.ruby-lang.org/