Bug #20288: `rb_fiber_scheduler_close` exceptions are not handled in `rb_fiber_scheduler_set`.

• Status: Closed
• Assignee: ioquatix (Samuel Williams)
• Target version: -
• Backport: 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED

[ioquatix (Samuel Williams)]

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.

[ioquatix (Samuel Williams)]

PR: https://github.com/ruby/ruby/pull/10042

[ioquatix (Samuel Williams)]

• Status changed from Open to Closed
• Backport changed from 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN to 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED, 3.3: REQUIRED