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When toggling perf trampoline while threads are running, or duringinterpreter finalization with daemon threads active, a use-after-freeoccurs. The munmap call in free_code_arenas releases executable memorywhile other threads may still be executing within trampolines orunwinding through them, causing SIGSEGV or SystemError.The fix uses reference counting with a code watcher. Each code objectthat receives a trampoline increments a refcount. When code objects aredestroyed, the watcher decrements the refcount and frees arenas onlywhen it reaches zero. This ensures trampolines are never freed whileany code object could still reference them.