Fixes and refinements to dynamic borrow checking

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - Unreleased
   - Add dynamic borrow checking to safely construct references into the interior of NumPy arrays. ([#274](https://github.com/PyO3/rust-numpy/pull/274))
+    - The deprecated iterator builders `NpySingleIterBuilder::{readonly,readwrite}` and `NpyMultiIterBuilder::add_{readonly,readwrite}` now take referencces to `PyReadonlyArray` and `PyReadwriteArray` instead of consuming them.
+    - The destructive `PyArray::resize` method is now unsafe if used without an instance of `PyReadwriteArray`. ([#302](https://github.com/PyO3/rust-numpy/pull/302))
   - The `inner`, `dot` and `einsum` functions can also return a scalar instead of a zero-dimensional array to match NumPy's types ([#285](https://github.com/PyO3/rust-numpy/pull/285))
   - Deprecate `PyArray::from_exact_iter` after optimizing `PyArray::from_iter`. ([#292](https://github.com/PyO3/rust-numpy/pull/292))
 

src/array.rs

@@ -23,7 +23,7 @@ use crate::borrow::{PyReadonlyArray, PyReadwriteArray};
 use crate::cold;
 use crate::convert::{ArrayExt, IntoPyArray, NpyIndex, ToNpyDims, ToPyArray};
 use crate::dtype::{Element, PyArrayDescr};
-use crate::error::{DimensionalityError, FromVecError, NotContiguousError, TypeError};
+use crate::error::{BorrowError, DimensionalityError, FromVecError, NotContiguousError, TypeError};
 use crate::npyffi::{self, npy_intp, NPY_ORDER, PY_ARRAY_API};
 use crate::slice_container::PySliceContainer;
 
@@ -846,13 +846,33 @@ impl<T: Element, D: Dimension> PyArray<T, D> {
     }
 
     /// Get an immutable borrow of the NumPy array
+    pub fn try_readonly(&self) -> Result<PyReadonlyArray<'_, T, D>, BorrowError> {
+        PyReadonlyArray::try_new(self)
+    }
+
+    /// Get an immutable borrow of the NumPy array
+    ///
+    /// # Panics
+    ///
+    /// Panics if the allocation backing the array is currently mutably borrowed.
+    /// For a non-panicking variant, use [`try_readonly`][Self::try_readonly].
     pub fn readonly(&self) -> PyReadonlyArray<'_, T, D> {
-        PyReadonlyArray::try_new(self).unwrap()
+        self.try_readonly().unwrap()
     }
 
     /// Get a mutable borrow of the NumPy array
+    pub fn try_readwrite(&self) -> Result<PyReadwriteArray<'_, T, D>, BorrowError> {
+        PyReadwriteArray::try_new(self)
+    }
+
+    /// Get a mutable borrow of the NumPy array
+    ///
+    /// # Panics
+    ///
+    /// Panics if the allocation backing the array is currently borrowed.
+    /// For a non-panicking variant, use [`try_readwrite`][Self::try_readwrite].
     pub fn readwrite(&self) -> PyReadwriteArray<'_, T, D> {
-        PyReadwriteArray::try_new(self).unwrap()
+        self.try_readwrite().unwrap()
     }
 
     /// Returns the internal array as [`ArrayView`].
@@ -1057,19 +1077,30 @@ impl<T: Element> PyArray<T, Ix1> {
         data.into_pyarray(py)
     }
 
-    /// Extends or trancates the length of 1 dimension PyArray.
+    /// Extends or truncates the length of a one-dimensional array.
+    ///
+    /// # Safety
+    ///
+    /// There should be no outstanding references (shared or exclusive) into the array
+    /// as this method might re-allocate it and thereby invalidate all pointers into it.
     ///
     /// # Example
+    ///
     /// ```
     /// use numpy::PyArray;
-    /// pyo3::Python::with_gil(|py| {
+    /// use pyo3::Python;
+    ///
+    /// Python::with_gil(|py| {
     ///     let pyarray = PyArray::arange(py, 0, 10, 1);
     ///     assert_eq!(pyarray.len(), 10);
-    ///     pyarray.resize(100).unwrap();
+    ///
+    ///     unsafe {
+    ///         pyarray.resize(100).unwrap();
+    ///     }
     ///     assert_eq!(pyarray.len(), 100);
     /// });
     /// ```
-    pub fn resize(&self, new_elems: usize) -> PyResult<()> {
+    pub unsafe fn resize(&self, new_elems: usize) -> PyResult<()> {
         self.resize_(self.py(), [new_elems], 1, NPY_ORDER::NPY_ANYORDER)
     }
 

src/borrow.rs

@@ -170,6 +170,86 @@ impl BorrowFlags {
     unsafe fn get(&self) -> &mut HashMap<usize, isize> {
         (*self.0.get()).get_or_insert_with(HashMap::new)
     }
+
+    fn acquire<T, D>(&self, array: &PyArray<T, D>) -> Result<(), BorrowError> {
+        let address = base_address(array);
+
+        // SAFETY: Access to `&PyArray<T, D>` implies holding the GIL
+        // and we are not calling into user code which might re-enter this function.
+        let borrow_flags = unsafe { BORROW_FLAGS.get() };
+
+        match borrow_flags.entry(address) {
+            Entry::Occupied(entry) => {
+                let readers = entry.into_mut();
+
+                let new_readers = readers.wrapping_add(1);
+
+                if new_readers <= 0 {
+                    cold();
+                    return Err(BorrowError::AlreadyBorrowed);
+                }
+
+                *readers = new_readers;
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(1);
+            }
+        }
+
+        Ok(())
+    }
+
+    fn release<T, D>(&self, array: &PyArray<T, D>) {
+        let address = base_address(array);
+
+        // SAFETY: Access to `&PyArray<T, D>` implies holding the GIL
+        // and we are not calling into user code which might re-enter this function.
+        let borrow_flags = unsafe { BORROW_FLAGS.get() };
+
+        let readers = borrow_flags.get_mut(&address).unwrap();
+
+        *readers -= 1;
+
+        if *readers == 0 {
+            borrow_flags.remove(&address).unwrap();
+        }
+    }
+
+    fn acquire_mut<T, D>(&self, array: &PyArray<T, D>) -> Result<(), BorrowError> {
+        let address = base_address(array);
+
+        // SAFETY: Access to `&PyArray<T, D>` implies holding the GIL
+        // and we are not calling into user code which might re-enter this function.
+        let borrow_flags = unsafe { BORROW_FLAGS.get() };
+
+        match borrow_flags.entry(address) {
+            Entry::Occupied(entry) => {
+                let writers = entry.into_mut();
+
+                if *writers != 0 {
+                    cold();
+                    return Err(BorrowError::AlreadyBorrowed);
+                }
+
+                *writers = -1;
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(-1);
+            }
+        }
+
+        Ok(())
+    }
+
+    fn release_mut<T, D>(&self, array: &PyArray<T, D>) {
+        let address = base_address(array);
+
+        // SAFETY: Access to `&PyArray<T, D>` implies holding the GIL
+        // and we are not calling into user code which might re-enter this function.
+        let borrow_flags = unsafe { self.get() };
+
+        borrow_flags.remove(&address).unwrap();
+    }
 }
 
 static BORROW_FLAGS: BorrowFlags = BorrowFlags::new();
@@ -224,29 +304,7 @@ where
     D: Dimension,
 {
     pub(crate) fn try_new(array: &'py PyArray<T, D>) -> Result<Self, BorrowError> {
-        let address = base_address(array);
-
-        // SAFETY: Access to a `&'py PyArray<T, D>` implies holding the GIL
-        // and we are not calling into user code which might re-enter this function.
-        let borrow_flags = unsafe { BORROW_FLAGS.get() };
-
-        match borrow_flags.entry(address) {
-            Entry::Occupied(entry) => {
-                let readers = entry.into_mut();
-
-                let new_readers = readers.wrapping_add(1);
-
-                if new_readers <= 0 {
-                    cold();
-                    return Err(BorrowError::AlreadyBorrowed);
-                }
-
-                *readers = new_readers;
-            }
-            Entry::Vacant(entry) => {
-                entry.insert(1);
-            }
-        }
+        BORROW_FLAGS.acquire(array)?;
 
         Ok(Self(array))
     }
@@ -275,21 +333,19 @@ where
     }
 }
 
+impl<'a, T, D> Clone for PyReadonlyArray<'a, T, D>
+where
+    T: Element,
+    D: Dimension,
+{
+    fn clone(&self) -> Self {
+        Self::try_new(self.0).unwrap()
+    }
+}
+
 impl<'a, T, D> Drop for PyReadonlyArray<'a, T, D> {
     fn drop(&mut self) {
-        let address = base_address(self.0);
-
-        // SAFETY: Access to a `&'py PyArray<T, D>` implies holding the GIL
-        // and we are not calling into user code which might re-enter this function.
-        let borrow_flags = unsafe { BORROW_FLAGS.get() };
-
-        let readers = borrow_flags.get_mut(&address).unwrap();
-
-        *readers -= 1;
-
-        if *readers == 0 {
-            borrow_flags.remove(&address).unwrap();
-        }
+        BORROW_FLAGS.release(self.0);
     }
 }
 
@@ -348,27 +404,7 @@ where
             return Err(BorrowError::NotWriteable);
         }
 
-        let address = base_address(array);
-
-        // SAFETY: Access to a `&'py PyArray<T, D>` implies holding the GIL
-        // and we are not calling into user code which might re-enter this function.
-        let borrow_flags = unsafe { BORROW_FLAGS.get() };
-
-        match borrow_flags.entry(address) {
-            Entry::Occupied(entry) => {
-                let writers = entry.into_mut();
-
-                if *writers != 0 {
-                    cold();
-                    return Err(BorrowError::AlreadyBorrowed);
-                }
-
-                *writers = -1;
-            }
-            Entry::Vacant(entry) => {
-                entry.insert(-1);
-            }
-        }
+        BORROW_FLAGS.acquire_mut(array)?;
 
         Ok(Self(array))
     }
@@ -397,15 +433,44 @@ where
     }
 }
 
-impl<'a, T, D> Drop for PyReadwriteArray<'a, T, D> {
-    fn drop(&mut self) {
-        let address = base_address(self.0);
+impl<'py, T> PyReadwriteArray<'py, T, Ix1>
+where
+    T: Element,
+{
+    /// Extends or truncates the length of a one-dimensional array.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use numpy::PyArray;
+    /// use pyo3::Python;
+    ///
+    /// Python::with_gil(|py| {
+    ///     let pyarray = PyArray::arange(py, 0, 10, 1);
+    ///     assert_eq!(pyarray.len(), 10);
+    ///
+    ///     let pyarray = pyarray.readwrite();
+    ///     let pyarray = pyarray.resize(100).unwrap();
+    ///     assert_eq!(pyarray.len(), 100);
+    /// });
+    /// ```
+    pub fn resize(self, new_elems: usize) -> PyResult<Self> {
+        BORROW_FLAGS.release_mut(self.0);
+
+        // SAFETY: Ownership of `self` proves exclusive access to the interior of the array.
+        unsafe {
+            self.0.resize(new_elems)?;
+        }
 
-        // SAFETY: Access to a `&'py PyArray<T, D>` implies holding the GIL
-        // and we are not calling into user code which might re-enter this function.
-        let borrow_flags = unsafe { BORROW_FLAGS.get() };
+        BORROW_FLAGS.acquire_mut(self.0)?;
 
-        borrow_flags.remove(&address).unwrap();
+        Ok(self)
+    }
+}
+
+impl<'a, T, D> Drop for PyReadwriteArray<'a, T, D> {
+    fn drop(&mut self) {
+        BORROW_FLAGS.release_mut(self.0);
     }
 }
 

src/convert.rs

@@ -29,7 +29,9 @@ use crate::sealed::Sealed;
 ///     assert_eq!(py_array.readonly().as_slice().unwrap(), &[1, 2, 3]);
 ///
 ///     // Array cannot be resized when its data is owned by Rust.
-///     assert!(py_array.resize(100).is_err());
+///     unsafe {
+///         assert!(py_array.resize(100).is_err());
+///     }
 /// });
 /// ```
 pub trait IntoPyArray {

tests/borrow.rs

@@ -115,6 +115,19 @@ fn borrows_span_threads() {
     });
 }
 
+#[test]
+fn shared_borrows_can_be_cloned() {
+    Python::with_gil(|py| {
+        let array = PyArray::<f64, _>::zeros(py, (1, 2, 3), false);
+
+        let shared1 = array.readonly();
+        let shared2 = shared1.clone();
+
+        assert_eq!(shared2.shape(), [1, 2, 3]);
+        assert_eq!(shared1.shape(), [1, 2, 3]);
+    });
+}
+
 #[test]
 #[should_panic(expected = "AlreadyBorrowed")]
 fn overlapping_views_conflict() {
@@ -235,3 +248,17 @@ fn readwrite_as_array_slice() {
         assert_eq!(*array.get_mut([0, 1, 2]).unwrap(), 0.0);
     });
 }
+
+#[test]
+fn resize_using_exclusive_borrow() {
+    Python::with_gil(|py| {
+        let array = PyArray::<f64, _>::zeros(py, 3, false);
+        assert_eq!(array.shape(), [3]);
+
+        let mut array = array.readwrite();
+        assert_eq!(array.as_slice_mut().unwrap(), &[0.0; 3]);
+
+        let mut array = array.resize(5).unwrap();
+        assert_eq!(array.as_slice_mut().unwrap(), &[0.0; 5]);
+    });
+}

tests/to_py.rs

@@ -161,7 +161,9 @@ fn into_pyarray_cannot_resize() {
     Python::with_gil(|py| {
         let arr = vec![1, 2, 3].into_pyarray(py);
 
-        assert!(arr.resize(100).is_err())
+        unsafe {
+            assert!(arr.resize(100).is_err());
+        }
     });
 }