annotate rust/hg-cpython/src/pybytes_deref.rs @ 51199:16d477bb0078

rust-index: return variables systematic naming convention To help knowing at a glance when a method is ready, making us more comofortable when we are close to the final removal of scaffolding, we introduce the systematic variable names `rust_res` and `c_res`. The goal of this series is to always return the formet. We take again the case of `pack_header` as example. Our personal opinion is to usually avoid such poor semantics as `res`, but usually accept it when it close to the actual return, which will be the case in most methods of this series. Also, the name can simply be dropped when we remove the scaffolding. To follow on the example, the body of `pack_header()` should become this in the final version: ``` let index = self.index(py).borrow(); let packed = index.pack_header(args.get_item(py, 0).extract(py)?); Ok(PyBytes::new(py, &packed).into_object()); ``` in these cases it is close to the actual return and will be removed at the end entirely.
author Georges Racinet <georges.racinet@octobus.net>
date Sat, 30 Sep 2023 16:15:56 +0200
parents be3b545c5cff
children 7346f93be7a4
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1 use cpython::{PyBytes, Python};
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2 use stable_deref_trait::StableDeref;
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3
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4 /// Safe abstraction over a `PyBytes` together with the `&[u8]` slice
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5 /// that borrows it. Implements `Deref<Target = [u8]>`.
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6 ///
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7 /// Calling `PyBytes::data` requires a GIL marker but we want to access the
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8 /// data in a thread that (ideally) does not need to acquire the GIL.
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9 /// This type allows separating the call an the use.
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10 ///
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11 /// It also enables using a (wrapped) `PyBytes` in GIL-unaware generic code.
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12 pub struct PyBytesDeref {
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13 #[allow(unused)]
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14 keep_alive: PyBytes,
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15
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16 /// Borrows the buffer inside `self.keep_alive`,
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17 /// but the borrow-checker cannot express self-referential structs.
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18 data: *const [u8],
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19 }
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20
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21 impl PyBytesDeref {
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22 pub fn new(py: Python, bytes: PyBytes) -> Self {
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23 Self {
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24 data: bytes.data(py),
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25 keep_alive: bytes,
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26 }
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27 }
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28
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29 pub fn unwrap(self) -> PyBytes {
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30 self.keep_alive
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31 }
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32 }
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33
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34 impl std::ops::Deref for PyBytesDeref {
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35 type Target = [u8];
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36
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37 fn deref(&self) -> &[u8] {
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38 // Safety: the raw pointer is valid as long as the PyBytes is still
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39 // alive, and the returned slice borrows `self`.
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40 unsafe { &*self.data }
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41 }
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42 }
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43
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44 unsafe impl StableDeref for PyBytesDeref {}
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45
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46 fn require_send<T: Send>() {}
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48 #[allow(unused)]
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49 fn static_assert_pybytes_is_send() {
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50 #[allow(clippy::no_effect)]
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51 require_send::<PyBytes>;
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52 }
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53
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54 // Safety: PyBytes is Send. Raw pointers are not by default,
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55 // but here sending one to another thread is fine since we ensure it stays
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56 // valid.
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57 unsafe impl Send for PyBytesDeref {}