Method f_back

crates/vm/src/builtins/frame.rs:716–755

(&self, vm: &VirtualMachine)

    #[pygetset]
    pub fn f_back(&self, vm: &VirtualMachine) -> Option<PyRef<Frame>> {
        let previous = self.previous_frame();
        if previous.is_null() {
            return None;
        }

        if let Some(frame) = vm
            .frames
            .borrow()
            .iter()
            .find(|fp| {
                // SAFETY: the caller keeps the FrameRef alive while it's in the Vec
                let py: &crate::Py<Frame> = unsafe { fp.as_ref() };
                let ptr: *const Frame = &**py;
                core::ptr::eq(ptr, previous)
            })
            .map(|fp| unsafe { fp.as_ref() }.to_owned())
        {
            return Some(frame);
        }

        #[cfg(feature = "threading")]
        {
            let registry = vm.state.thread_frames.lock();
            for slot in registry.values() {
                let frames = slot.frames.lock();
                // SAFETY: the owning thread can't pop while we hold the Mutex,
                // so FramePtr is valid for the duration of the lock.
                if let Some(frame) = frames.iter().find_map(|fp| {
                    let f = unsafe { fp.as_ref() };
                    let ptr: *const Frame = &**f;
                    core::ptr::eq(ptr, previous).then(|| f.to_owned())
                }) {
                    return Some(frame);
                }
            }
        }

        None
    }
}