Remove ptr-int transmute by converting UnsafeWeakPointer from usize to *mut T

Cargo.toml

@@ -39,7 +39,7 @@ unstable-debug-counters = ["future"]
 
 [dependencies]
 crossbeam-channel = "0.5.4"
-crossbeam-epoch = "0.8.2"
+crossbeam-epoch = "0.9"
 crossbeam-utils = "0.8"
 num_cpus = "1.13"
 once_cell = "1.7"

src/common/unsafe_weak_pointer.rs

@@ -3,39 +3,31 @@ use std::sync::{Arc, Weak};
 /// WARNING: Do not use this struct unless you are absolutely sure what you are
 /// doing. Using this struct is unsafe and may cause memory related crashes and/or
 /// security vulnerabilities.
-///
-/// This struct exists with the sole purpose of avoiding compile errors relevant to
-/// the thread pool usages. The thread pool requires that the generic parameters on
-/// the `Cache` and `Inner` structs to have trait bounds `Send`, `Sync` and
-/// `'static`. This will be unacceptable for many cache usages.
-///
-/// This struct avoids the trait bounds by transmuting a pointer between
-/// `std::sync::Weak<Inner<K, V, S>>` and `usize`.
-///
-/// If you know a better solution than this, we would love te hear it.
-pub(crate) struct UnsafeWeakPointer {
+pub(crate) struct UnsafeWeakPointer<T> {
     // This is a std::sync::Weak pointer to Inner<K, V, S>.
-    raw_ptr: usize,
+    raw_ptr: *mut T,
 }
 
-impl UnsafeWeakPointer {
-    pub(crate) fn from_weak_arc<T>(p: Weak<T>) -> Self {
+unsafe impl<T> Send for UnsafeWeakPointer<T> {}
+
+impl<T> UnsafeWeakPointer<T> {
+    pub(crate) fn from_weak_arc(p: Weak<T>) -> Self {
         Self {
-            raw_ptr: unsafe { std::mem::transmute(p) },
+            raw_ptr: p.into_raw() as *mut T,
         }
     }
 
-    pub(crate) unsafe fn as_weak_arc<T>(&self) -> Weak<T> {
-        std::mem::transmute(self.raw_ptr)
+    pub(crate) unsafe fn as_weak_arc(&self) -> Weak<T> {
+        Weak::from_raw(self.raw_ptr.cast())
     }
 
-    pub(crate) fn forget_arc<T>(p: Arc<T>) {
+    pub(crate) fn forget_arc(p: Arc<T>) {
         // Downgrade the Arc to Weak, then forget.
         let weak = Arc::downgrade(&p);
         std::mem::forget(weak);
     }
 
-    pub(crate) fn forget_weak_arc<T>(p: Weak<T>) {
+    pub(crate) fn forget_weak_arc(p: Weak<T>) {
         std::mem::forget(p);
     }
 }
@@ -46,7 +38,7 @@ impl UnsafeWeakPointer {
 ///
 /// When you want to drop the Weak pointer, ensure that you drop it only once for the
 /// same `raw_ptr` across clones.
-impl Clone for UnsafeWeakPointer {
+impl<T> Clone for UnsafeWeakPointer<T> {
     fn clone(&self) -> Self {
         Self {
             raw_ptr: self.raw_ptr,

src/sync/housekeeper.rs

@@ -39,7 +39,7 @@ pub(crate) trait InnerSync {
 }
 
 pub(crate) struct Housekeeper<T> {
-    inner: Arc<Mutex<UnsafeWeakPointer>>,
+    inner: Arc<Mutex<UnsafeWeakPointer<T>>>,
     thread_pool: Arc<ThreadPool>,
     is_shutting_down: Arc<AtomicBool>,
     periodical_sync_job: Mutex<Option<JobHandle>>,
@@ -73,12 +73,12 @@ impl<T> Drop for Housekeeper<T> {
 
         // All sync jobs should have been finished by now. Clean other stuff up.
         ThreadPoolRegistry::release_pool(&self.thread_pool);
-        std::mem::drop(unsafe { self.inner.lock().as_weak_arc::<T>() });
+        std::mem::drop(unsafe { self.inner.lock().as_weak_arc() });
     }
 }
 
 // functions/methods used by Cache
-impl<T: InnerSync> Housekeeper<T> {
+impl<T: InnerSync> Housekeeper<T> where T: 'static {
     pub(crate) fn new(inner: Weak<T>) -> Self {
         use crate::common::thread_pool::PoolName;
 
@@ -107,7 +107,7 @@ impl<T: InnerSync> Housekeeper<T> {
 
     fn start_periodical_sync_job(
         thread_pool: &Arc<ThreadPool>,
-        unsafe_weak_ptr: Arc<Mutex<UnsafeWeakPointer>>,
+        unsafe_weak_ptr: Arc<Mutex<UnsafeWeakPointer<T>>>,
         is_shutting_down: Arc<AtomicBool>,
         periodical_sync_running: Arc<Mutex<()>>,
     ) -> JobHandle {
@@ -173,10 +173,10 @@ impl<T: InnerSync> Housekeeper<T> {
 
 // private functions/methods
 impl<T: InnerSync> Housekeeper<T> {
-    fn call_sync(unsafe_weak_ptr: &Arc<Mutex<UnsafeWeakPointer>>) -> Option<SyncPace> {
+    fn call_sync(unsafe_weak_ptr: &Arc<Mutex<UnsafeWeakPointer<T>>>) -> Option<SyncPace> {
         let lock = unsafe_weak_ptr.lock();
         // Restore the Weak pointer to Inner<K, V, S>.
-        let weak = unsafe { lock.as_weak_arc::<T>() };
+        let weak = unsafe { lock.as_weak_arc() };
         if let Some(inner) = weak.upgrade() {
             // TODO: Protect this call with catch_unwind().
             let sync_pace = inner.sync(MAX_SYNC_REPEATS);

src/sync/invalidator.rs

@@ -288,7 +288,7 @@ impl<K, V, S> Invalidator<K, V, S> {
 
 struct ScanContext<K, V, S> {
     predicates: Mutex<Vec<Predicate<K, V>>>,
-    cache: Mutex<UnsafeWeakPointer>,
+    cache: Mutex<UnsafeWeakPointer<Inner<K, V, S>>>,
     result: Mutex<Option<ScanResult<K, V>>>,
     is_running: AtomicBool,
     is_shutting_down: AtomicBool,
@@ -373,7 +373,7 @@ where
         let cache_lock = self.scan_context.cache.lock();
 
         // Restore the Weak pointer to Inner<K, V, S>.
-        let weak = unsafe { cache_lock.as_weak_arc::<Inner<K, V, S>>() };
+        let weak = unsafe { cache_lock.as_weak_arc() };
         if let Some(inner_cache) = weak.upgrade() {
             // TODO: Protect this call with catch_unwind().
             *self.scan_context.result.lock() = Some(self.do_execute(&inner_cache));