Handle EINTR retry in os.write() (PEP 475) (#7482)

* Handle EINTR retry in os.write() (PEP 475)

Add EINTR retry loop to os.write(), matching the existing
pattern in os.read() and os.readinto(). Remove the
expectedFailure marker from test_write in _test_eintr.py.

* Add atomic snapshot for dict/dict_keys in extract_elements

Add fast paths for dict and dict_keys types in
extract_elements_with, matching _list_extend() in CPython
Objects/listobject.c. Each branch takes an atomic snapshot
under a single read lock, preventing race conditions from
concurrent dict mutation without the GIL.

Remove expectedFailure from test_thread_safety.

Lib/test/_test_eintr.py

@@ -163,7 +163,6 @@ class OSEINTRTest(EINTRBaseTest):
             self.assertEqual(os.readinto(fd, buffer), len(expected))
             self.assertEqual(buffer, expected)
 
-    @unittest.expectedFailure  # TODO: RUSTPYTHON; InterruptedError: [Errno 4] Interrupted system call
     def test_write(self):
         rd, wr = os.pipe()
         self.addCleanup(os.close, wr)

Lib/test/_test_multiprocessing.py

@@ -4814,8 +4814,6 @@ class _TestFinalize(BaseTestCase):
         self.assertEqual(result, ['a', 'b', 'd10', 'd03', 'd02', 'd01', 'e'])
 
     @support.requires_resource('cpu')
-    # TODO: RUSTPYTHON; dict iteration races with concurrent GC mutations
-    @unittest.expectedFailure
     def test_thread_safety(self):
         # bpo-24484: _run_finalizers() should be thread-safe
         def cb():

crates/vm/src/stdlib/os.rs

@@ -321,12 +321,19 @@ pub(super) mod _os {
     }
 
     #[pyfunction]
-    fn write(
-        fd: crt_fd::Borrowed<'_>,
-        data: ArgBytesLike,
-        vm: &VirtualMachine,
-    ) -> io::Result<usize> {
-        data.with_ref(|b| vm.allow_threads(|| crt_fd::write(fd, b)))
+    fn write(fd: crt_fd::Borrowed<'_>, data: ArgBytesLike, vm: &VirtualMachine) -> PyResult<usize> {
+        data.with_ref(|b| {
+            loop {
+                match vm.allow_threads(|| crt_fd::write(fd, b)) {
+                    Ok(n) => return Ok(n),
+                    Err(e) if e.raw_os_error() == Some(libc::EINTR) => {
+                        vm.check_signals()?;
+                        continue;
+                    }
+                    Err(e) => return Err(e.into_pyexception(vm)),
+                }
+            }
+        })
     }
 
     #[cfg(not(windows))]

crates/vm/src/vm/mod.rs

@@ -22,7 +22,7 @@ use crate::{
         self, PyBaseExceptionRef, PyDict, PyDictRef, PyInt, PyList, PyModule, PyStr, PyStrInterned,
         PyStrRef, PyTypeRef, PyUtf8Str, PyUtf8StrInterned, PyWeak,
         code::PyCode,
-        dict::{PyDictItems, PyDictValues},
+        dict::{PyDictItems, PyDictKeys, PyDictValues},
         pystr::AsPyStr,
         tuple::PyTuple,
     },
@@ -1822,7 +1822,9 @@ impl VirtualMachine {
     where
         F: Fn(PyObjectRef) -> PyResult<T>,
     {
-        // Extract elements from item, if possible:
+        // Type-specific fast paths corresponding to _list_extend() in CPython
+        // Objects/listobject.c. Each branch takes an atomic snapshot to avoid
+        // race conditions from concurrent mutation (no GIL).
         let cls = value.class();
         let list_borrow;
         let slice = if cls.is(self.ctx.types.tuple_type) {
@@ -1830,8 +1832,13 @@ impl VirtualMachine {
         } else if cls.is(self.ctx.types.list_type) {
             list_borrow = value.downcast_ref::<PyList>().unwrap().borrow_vec();
             &list_borrow
+        } else if cls.is(self.ctx.types.dict_type) {
+            let keys = value.downcast_ref::<PyDict>().unwrap().keys_vec();
+            return keys.into_iter().map(func).collect();
+        } else if cls.is(self.ctx.types.dict_keys_type) {
+            let keys = value.downcast_ref::<PyDictKeys>().unwrap().dict.keys_vec();
+            return keys.into_iter().map(func).collect();
         } else if cls.is(self.ctx.types.dict_values_type) {
-            // Atomic snapshot of dict values - prevents race condition during iteration
             let values = value
                 .downcast_ref::<PyDictValues>()
                 .unwrap()
@@ -1839,7 +1846,6 @@ impl VirtualMachine {
                 .values_vec();
             return values.into_iter().map(func).collect();
         } else if cls.is(self.ctx.types.dict_items_type) {
-            // Atomic snapshot of dict items - prevents race condition during iteration
             let items = value
                 .downcast_ref::<PyDictItems>()
                 .unwrap()