Mercurial > hg
view rust/hg-cpython/src/dirstate/dirs_multiset.rs @ 42752:30320c7bf79f
rust-cpython: add macro for sharing references
Following an experiment done by Georges Racinet, we now have a working way of
sharing references between Python and Rust. This is needed in many points of
the codebase, for example every time we need to expose an iterator to a
Rust-backed Python class.
In a few words, references are (unsafely) marked as `'static` and coupled
with manual reference counting; we are doing manual borrow-checking.
This changes introduces two declarative macro to help reduce boilerplate.
While it is better than not using macros, they are not perfect. They need to:
- Integrate with the garbage collector for container types (not needed
as of yet), as stated in the docstring
- Allow for leaking multiple attributes at the same time
- Inject the `py_shared_state` data attribute in `py_class`-generated
structs
- Automatically namespace the functions and attributes they generate
For at least the last two points, we will need to write a procedural macro
instead of a declarative one.
While this reference-sharing mechanism is being ironed out I thought it best
not to implement it yet.
Lastly, and implementation detail renders our Rust-backed Python iterators too
strict to be proper drop-in replacements, as will be illustrated in a future
patch: if the data structure referenced by a non-depleted iterator is mutated,
an `AlreadyBorrowed` exception is raised, whereas Python would allow it, only
to raise a `RuntimeError` if `next` is called on said iterator. This will have
to be addressed at some point.
Differential Revision: https://phab.mercurial-scm.org/D6631
author | Raphaël Gomès <rgomes@octobus.net> |
---|---|
date | Tue, 09 Jul 2019 15:15:54 +0200 |
parents | 849e744b925d |
children | 2e1f74cc3350 |
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// dirs_multiset.rs // // Copyright 2019 Raphaël Gomès <rgomes@octobus.net> // // This software may be used and distributed according to the terms of the // GNU General Public License version 2 or any later version. //! Bindings for the `hg::dirstate::dirs_multiset` file provided by the //! `hg-core` package. use std::cell::RefCell; use std::convert::TryInto; use cpython::{ exc, ObjectProtocol, PyBytes, PyClone, PyDict, PyErr, PyObject, PyResult, Python, }; use crate::{dirstate::extract_dirstate, ref_sharing::PySharedState}; use hg::{ DirsIterable, DirsMultiset, DirstateMapError, DirstateParseError, EntryState, }; py_class!(pub class Dirs |py| { data inner: RefCell<DirsMultiset>; data py_shared_state: PySharedState; // `map` is either a `dict` or a flat iterator (usually a `set`, sometimes // a `list`) def __new__( _cls, map: PyObject, skip: Option<PyObject> = None ) -> PyResult<Self> { let mut skip_state: Option<EntryState> = None; if let Some(skip) = skip { skip_state = Some( skip.extract::<PyBytes>(py)?.data(py)[0] .try_into() .map_err(|e: DirstateParseError| { PyErr::new::<exc::ValueError, _>(py, e.to_string()) })?, ); } let inner = if let Ok(map) = map.cast_as::<PyDict>(py) { let dirstate = extract_dirstate(py, &map)?; DirsMultiset::new( DirsIterable::Dirstate(&dirstate), skip_state, ) } else { let map: Result<Vec<Vec<u8>>, PyErr> = map .iter(py)? .map(|o| Ok(o?.extract::<PyBytes>(py)?.data(py).to_owned())) .collect(); DirsMultiset::new( DirsIterable::Manifest(&map?), skip_state, ) }; Self::create_instance( py, RefCell::new(inner), PySharedState::default() ) } def addpath(&self, path: PyObject) -> PyResult<PyObject> { self.borrow_mut(py)?.add_path( path.extract::<PyBytes>(py)?.data(py), ); Ok(py.None()) } def delpath(&self, path: PyObject) -> PyResult<PyObject> { self.borrow_mut(py)?.delete_path( path.extract::<PyBytes>(py)?.data(py), ) .and(Ok(py.None())) .or_else(|e| { match e { DirstateMapError::PathNotFound(_p) => { Err(PyErr::new::<exc::ValueError, _>( py, "expected a value, found none".to_string(), )) } DirstateMapError::EmptyPath => { Ok(py.None()) } } }) } def __iter__(&self) -> PyResult<DirsMultisetKeysIterator> { DirsMultisetKeysIterator::create_instance( py, RefCell::new(Some(DirsMultisetLeakedRef::new(py, &self))), RefCell::new(Box::new(self.leak_immutable(py)?.iter())), ) } def __contains__(&self, item: PyObject) -> PyResult<bool> { Ok(self .inner(py) .borrow() .contains(item.extract::<PyBytes>(py)?.data(py).as_ref())) } }); py_shared_ref!(Dirs, DirsMultiset, inner, DirsMultisetLeakedRef,); impl Dirs { pub fn from_inner(py: Python, d: DirsMultiset) -> PyResult<Self> { Self::create_instance(py, RefCell::new(d), PySharedState::default()) } fn translate_key(py: Python, res: &Vec<u8>) -> PyResult<Option<PyBytes>> { Ok(Some(PyBytes::new(py, res))) } } py_shared_sequence_iterator!( DirsMultisetKeysIterator, DirsMultisetLeakedRef, Vec<u8>, Dirs::translate_key, Option<PyBytes> );