Auto merge of rust-lang#136772 - safinaskar:parallel-2025-02-08-11-55, r=<try>

parallel: rustc_data_structures: sync: implement RwLock as enum { Sync(parking_lot::RwLock), NoSync(RefCell) }

parallel: rustc_data_structures: sync: implement `RwLock` as `enum { Sync(parking_lot::RwLock), NoSync(RefCell) }`

Hopefully this will make single threaded front end faster.

I carefully split changes into commits. Commit messages are self-explanatory. Squashing is not recommended.

cc "Parallel Rustc Front-end" rust-lang#113349

r? SparrowLii

`@rustbot` label: +WG-compiler-parallel

Author: bors

compiler/rustc_data_structures/src/sync.rs

@@ -111,11 +111,7 @@ pub use std::sync::atomic::{AtomicBool, AtomicU32, AtomicUsize};
 pub use std::sync::{OnceLock, Weak};
 
 pub use mode::{is_dyn_thread_safe, set_dyn_thread_safe_mode};
-pub use parking_lot::{
-    MappedMutexGuard as MappedLockGuard, MappedRwLockReadGuard as MappedReadGuard,
-    MappedRwLockWriteGuard as MappedWriteGuard, RwLockReadGuard as ReadGuard,
-    RwLockWriteGuard as WriteGuard,
-};
+pub use parking_lot::MappedMutexGuard as MappedLockGuard;
 #[cfg(not(target_has_atomic = "64"))]
 pub use portable_atomic::AtomicU64;
 
@@ -151,12 +147,6 @@ impl<T> MTLock<T> {
     }
 }
 
-use parking_lot::RwLock as InnerRwLock;
-
-/// This makes locks panic if they are already held.
-/// It is only useful when you are running in a single thread
-const ERROR_CHECKING: bool = false;
-
 pub type MTLockRef<'a, T> = LRef<'a, MTLock<T>>;
 
 #[derive(Default)]
@@ -175,85 +165,7 @@ impl<K: Eq + Hash, V: Eq, S: BuildHasher> HashMapExt<K, V> for HashMap<K, V, S>
     }
 }
 
-#[derive(Debug, Default)]
-pub struct RwLock<T>(InnerRwLock<T>);
-
-impl<T> RwLock<T> {
-    #[inline(always)]
-    pub fn new(inner: T) -> Self {
-        RwLock(InnerRwLock::new(inner))
-    }
-
-    #[inline(always)]
-    pub fn into_inner(self) -> T {
-        self.0.into_inner()
-    }
-
-    #[inline(always)]
-    pub fn get_mut(&mut self) -> &mut T {
-        self.0.get_mut()
-    }
-
-    #[inline(always)]
-    pub fn read(&self) -> ReadGuard<'_, T> {
-        if ERROR_CHECKING {
-            self.0.try_read().expect("lock was already held")
-        } else {
-            self.0.read()
-        }
-    }
-
-    #[inline(always)]
-    #[track_caller]
-    pub fn with_read_lock<F: FnOnce(&T) -> R, R>(&self, f: F) -> R {
-        f(&*self.read())
-    }
-
-    #[inline(always)]
-    pub fn try_write(&self) -> Result<WriteGuard<'_, T>, ()> {
-        self.0.try_write().ok_or(())
-    }
-
-    #[inline(always)]
-    pub fn write(&self) -> WriteGuard<'_, T> {
-        if ERROR_CHECKING {
-            self.0.try_write().expect("lock was already held")
-        } else {
-            self.0.write()
-        }
-    }
-
-    #[inline(always)]
-    #[track_caller]
-    pub fn with_write_lock<F: FnOnce(&mut T) -> R, R>(&self, f: F) -> R {
-        f(&mut *self.write())
-    }
-
-    #[inline(always)]
-    #[track_caller]
-    pub fn borrow(&self) -> ReadGuard<'_, T> {
-        self.read()
-    }
-
-    #[inline(always)]
-    #[track_caller]
-    pub fn borrow_mut(&self) -> WriteGuard<'_, T> {
-        self.write()
-    }
-
-    #[inline(always)]
-    pub fn leak(&self) -> &T {
-        let guard = self.read();
-        let ret = unsafe { &*(&raw const *guard) };
-        std::mem::forget(guard);
-        ret
-    }
-}
-
-// FIXME: Probably a bad idea
-impl<T: Clone> Clone for RwLock<T> {
-    #[inline]
-    fn clone(&self) -> Self {
-        RwLock::new(self.borrow().clone())
-    }
-}
+mod rwlock;
+pub use rwlock::{
+    MappedReadGuard, MappedWriteGuard, ReadError, ReadGuard, RwLock, WriteError, WriteGuard,
+};