Fix generation race condition with sync storage (#2638)

* Fix generation race condition with sync storage

* Document GenerationalPointer

* check generation before recycling generational box

* fix clippy

* make race_condition_regression test panic if it fails

packages/generational-box/tests/errors.rs

@@ -1,38 +1,33 @@
-use std::cell::{Ref, RefMut};
-
 use generational_box::{
-    AlreadyBorrowedError, AlreadyBorrowedMutError, AnyStorage, BorrowError, BorrowMutError,
-    GenerationalBox, GenerationalRef, GenerationalRefMut, Owner, UnsyncStorage, ValueDroppedError,
+    AlreadyBorrowedError, AlreadyBorrowedMutError, BorrowError, BorrowMutError, GenerationalBox,
+    Owner, Storage, SyncStorage, UnsyncStorage, ValueDroppedError,
 };
 
 #[track_caller]
-fn read_at_location(
-    value: GenerationalBox<i32>,
-) -> (
-    GenerationalRef<Ref<'static, i32>>,
-    &'static std::panic::Location<'static>,
-) {
+fn read_at_location<S: Storage<i32>>(
+    value: GenerationalBox<i32, S>,
+) -> (S::Ref<'static, i32>, &'static std::panic::Location<'static>) {
     let location = std::panic::Location::caller();
     let read = value.read();
     (read, location)
 }
 
 #[track_caller]
-fn write_at_location(
-    value: GenerationalBox<i32>,
-) -> (
-    GenerationalRefMut<RefMut<'static, i32>>,
-    &'static std::panic::Location<'static>,
-) {
+fn write_at_location<S: Storage<i32>>(
+    value: GenerationalBox<i32, S>,
+) -> (S::Mut<'static, i32>, &'static std::panic::Location<'static>) {
     let location = std::panic::Location::caller();
     let write = value.write();
     (write, location)
 }
 
 #[track_caller]
-fn create_at_location(
-    owner: &Owner,
-) -> (GenerationalBox<i32>, &'static std::panic::Location<'static>) {
+fn create_at_location<S: Storage<i32>>(
+    owner: &Owner<S>,
+) -> (
+    GenerationalBox<i32, S>,
+    &'static std::panic::Location<'static>,
+) {
     let location = std::panic::Location::caller();
     let value = owner.insert(1);
     (value, location)
@@ -40,65 +35,85 @@ fn create_at_location(
 
 #[test]
 fn read_while_writing_error() {
-    let owner = UnsyncStorage::owner();
-    let value = owner.insert(1);
+    fn read_while_writing_error_test<S: Storage<i32>>() {
+        let owner = S::owner();
+        let value = owner.insert(1);
 
-    let (write, location) = write_at_location(value);
+        let (write, location) = write_at_location(value);
 
-    assert_eq!(
-        value.try_read().err(),
-        Some(BorrowError::AlreadyBorrowedMut(
-            AlreadyBorrowedMutError::new(location)
-        ))
-    );
-    drop(write);
+        assert_eq!(
+            value.try_read().err(),
+            Some(BorrowError::AlreadyBorrowedMut(
+                AlreadyBorrowedMutError::new(location)
+            ))
+        );
+        drop(write);
+    }
+
+    // For sync storage this will deadlock
+    read_while_writing_error_test::<UnsyncStorage>();
 }
 
 #[test]
 fn read_after_dropped_error() {
-    let owner = UnsyncStorage::owner();
-    let (value, location) = create_at_location(&owner);
-    drop(owner);
-    assert_eq!(
-        value.try_read().err(),
-        Some(BorrowError::Dropped(ValueDroppedError::new(location)))
-    );
+    fn read_after_dropped_error_test<S: Storage<i32>>() {
+        let owner = S::owner();
+        let (value, location) = create_at_location(&owner);
+        drop(owner);
+        assert_eq!(
+            value.try_read().err(),
+            Some(BorrowError::Dropped(ValueDroppedError::new(location)))
+        );
+    }
+
+    read_after_dropped_error_test::<UnsyncStorage>();
+    read_after_dropped_error_test::<SyncStorage>();
 }
 
 #[test]
 fn write_while_writing_error() {
-    let owner = UnsyncStorage::owner();
-    let value = owner.insert(1);
+    fn write_while_writing_error_test<S: Storage<i32>>() {
+        let owner = S::owner();
+        let value = owner.insert(1);
 
-    #[allow(unused)]
-    let (write, location) = write_at_location(value);
+        #[allow(unused)]
+        let (write, location) = write_at_location(value);
 
-    let write_result = value.try_write();
-    assert!(write_result.is_err());
-    #[cfg(debug_assertions)]
-    assert_eq!(
-        write_result.err(),
-        Some(BorrowMutError::AlreadyBorrowedMut(
-            AlreadyBorrowedMutError::new(location)
-        ))
-    );
+        let write_result = value.try_write();
+        assert!(write_result.is_err());
+        #[cfg(any(debug_assertions, feature = "debug_borrows"))]
+        assert_eq!(
+            write_result.err(),
+            Some(BorrowMutError::AlreadyBorrowedMut(
+                AlreadyBorrowedMutError::new(location)
+            ))
+        );
 
-    drop(write);
+        drop(write);
+    }
+
+    // For sync storage this will deadlock
+    write_while_writing_error_test::<UnsyncStorage>();
 }
 
 #[test]
 fn write_while_reading_error() {
-    let owner = UnsyncStorage::owner();
-    let value = owner.insert(1);
+    fn write_while_reading_error_test<S: Storage<i32>>() {
+        let owner = S::owner();
+        let value = owner.insert(1);
 
-    let (read, location) = read_at_location(value);
+        let (read, location) = read_at_location(value);
 
-    assert_eq!(
-        value.try_write().err(),
-        Some(BorrowMutError::AlreadyBorrowed(AlreadyBorrowedError::new(
-            vec![location]
-        )))
-    );
+        assert_eq!(
+            value.try_write().err(),
+            Some(BorrowMutError::AlreadyBorrowed(AlreadyBorrowedError::new(
+                vec![location]
+            )))
+        );
 
-    drop(read);
+        drop(read);
+    }
+
+    // For sync storage this will deadlock
+    write_while_reading_error_test::<UnsyncStorage>();
 }