RFC: Add intern! macro which can be used to amortize the cost of creating Python objects by storing them inside a GILOnceCell.

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added methods on `InterpreterConfig` to run Python scripts using the configured executable. [#2092](https://github.com/PyO3/pyo3/pull/2092)
 - Added FFI definitions for `PyType_FromModuleAndSpec`, `PyType_GetModule`, `PyType_GetModuleState` and `PyModule_AddType`. [#2250](https://github.com/PyO3/pyo3/pull/2250)
 - Add `PyString::intern` to enable usage of the Python's built-in string interning. [#2268](https://github.com/PyO3/pyo3/pull/2268)
+- Add `intern!` macro which can be used to amortize the cost of creating Python strings by storing them inside a `GILOnceCell`. [#2269](https://github.com/PyO3/pyo3/pull/2269)
 
 ### Changed
 

Cargo.toml

@@ -142,6 +142,10 @@ harness = false
 name = "bench_tuple"
 harness = false
 
+[[bench]]
+name = "bench_intern"
+harness = false
+
 [workspace]
 members = [
     "pyo3-ffi",

benches/bench_intern.rs

@@ -0,0 +1,33 @@
+use criterion::{criterion_group, criterion_main, Bencher, Criterion};
+
+use pyo3::prelude::*;
+
+use pyo3::{intern, prepare_freethreaded_python};
+
+fn getattr_direct(b: &mut Bencher<'_>) {
+    prepare_freethreaded_python();
+
+    Python::with_gil(|py| {
+        let sys = py.import("sys").unwrap();
+
+        b.iter(|| sys.getattr("version").unwrap());
+    });
+}
+
+fn getattr_intern(b: &mut Bencher<'_>) {
+    prepare_freethreaded_python();
+
+    Python::with_gil(|py| {
+        let sys = py.import("sys").unwrap();
+
+        b.iter(|| sys.getattr(intern!(py, "version")).unwrap());
+    });
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    c.bench_function("getattr_direct", getattr_direct);
+    c.bench_function("getattr_intern", getattr_intern);
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

src/lib.rs

@@ -375,6 +375,7 @@ pub mod impl_;
 mod instance;
 pub mod marker;
 pub mod marshal;
+#[macro_use]
 pub mod once_cell;
 pub mod panic;
 pub mod prelude;

src/once_cell.rs

@@ -42,6 +42,7 @@ impl<T> GILOnceCell<T> {
     }
 
     /// Get a reference to the contained value, or `None` if the cell has not yet been written.
+    #[inline]
     pub fn get(&self, _py: Python<'_>) -> Option<&T> {
         // Safe because if the cell has not yet been written, None is returned.
         unsafe { &*self.0.get() }.as_ref()
@@ -61,15 +62,23 @@ impl<T> GILOnceCell<T> {
     ///     exactly once, even if multiple threads attempt to call `get_or_init`
     ///  4) if f() can panic but still does not release the GIL, it may be called multiple times,
     ///     but it is guaranteed that f() will never be called concurrently
+    #[inline]
     pub fn get_or_init<F>(&self, py: Python<'_>, f: F) -> &T
     where
         F: FnOnce() -> T,
     {
-        let inner = unsafe { &*self.0.get() }.as_ref();
-        if let Some(value) = inner {
+        if let Some(value) = self.get(py) {
             return value;
         }
 
+        self.init(py, f)
+    }
+
+    #[cold]
+    fn init<F>(&self, py: Python<'_>, f: F) -> &T
+    where
+        F: FnOnce() -> T,
+    {
         // Note that f() could temporarily release the GIL, so it's possible that another thread
         // writes to this GILOnceCell before f() finishes. That's fine; we'll just have to discard
         // the value computed here and accept a bit of wasted computation.
@@ -101,3 +110,69 @@ impl<T> GILOnceCell<T> {
         Ok(())
     }
 }
+
+/// Interns `text` as a Python string and stores a reference to it in static storage.
+///
+/// A reference to the same Python string is returned on each invocation.
+///
+/// # Example: Using `intern!` to avoid needlessly recreating the same Python string
+///
+/// ```
+/// use pyo3::intern;
+/// # use pyo3::{pyfunction, types::PyDict, PyResult, Python};
+///
+/// #[pyfunction]
+/// fn create_dict(py: Python<'_>) -> PyResult<&PyDict> {
+///    let dict = PyDict::new(py);
+///    //             👇 A new `PyString` is created
+///    //                for every call of this function.
+///    dict.set_item("foo", 42)?;
+///    Ok(dict)
+/// }
+///
+/// #[pyfunction]
+/// fn create_dict_faster(py: Python<'_>) -> PyResult<&PyDict> {
+///    let dict = PyDict::new(py);
+///    //               👇 A `PyString` is created once and reused
+///    //                  for the lifetime of the program.
+///    dict.set_item(intern!(py, "foo"), 42)?;
+///    Ok(dict)
+/// }
+/// ```
+#[macro_export]
+macro_rules! intern {
+    ($py: expr, $text: expr) => {{
+        static INTERNED: $crate::once_cell::GILOnceCell<$crate::Py<$crate::types::PyString>> =
+            $crate::once_cell::GILOnceCell::new();
+
+        INTERNED
+            .get_or_init($py, || {
+                $crate::conversion::IntoPy::into_py(
+                    $crate::types::PyString::intern($py, $text),
+                    $py,
+                )
+            })
+            .as_ref($py)
+    }};
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::types::PyDict;
+
+    #[test]
+    fn test_intern() {
+        Python::with_gil(|py| {
+            let foo1 = "foo";
+            let foo2 = intern!(py, "foo");
+            let foo3 = intern!(py, stringify!(foo));
+
+            let dict = PyDict::new(py);
+            dict.set_item(foo1, 42_usize).unwrap();
+            assert!(dict.contains(foo2).unwrap());
+            assert_eq!(dict.get_item(foo3).unwrap().extract::<usize>().unwrap(), 42);
+        });
+    }
+}

src/test_hygiene/misc.rs

@@ -27,3 +27,9 @@ enum Derive4 {
 
 crate::create_exception!(mymodule, CustomError, crate::exceptions::PyException);
 crate::import_exception!(socket, gaierror);
+
+#[allow(dead_code)]
+fn intern(py: crate::Python<'_>) {
+    let _foo = crate::intern!(py, "foo");
+    let _bar = crate::intern!(py, stringify!(bar));
+}