From b2555bd5456ee12b24777a4eb65dd80fdc788923 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20K=C3=A5re=20Alsaker?= <john.kare.alsaker@gmail.com>
Date: Thu, 31 May 2018 20:24:56 +0200
Subject: [PATCH] Make QueryWaiter use safe code

---
 src/librustc/ty/maps/job.rs | 54 +++++++++++++++----------------------
 1 file changed, 22 insertions(+), 32 deletions(-)

diff --git a/src/librustc/ty/maps/job.rs b/src/librustc/ty/maps/job.rs
index 8b8f8420163..1a0347b86ab 100644
--- a/src/librustc/ty/maps/job.rs
+++ b/src/librustc/ty/maps/job.rs
@@ -94,15 +94,15 @@ pub(super) fn await<'lcx>(
         #[cfg(parallel_queries)]
         {
             tls::with_related_context(tcx, move |icx| {
-                let mut waiter = QueryWaiter {
-                    query: &icx.query,
+                let mut waiter = Lrc::new(QueryWaiter {
+                    query: icx.query.clone(),
                     span,
-                    cycle: None,
+                    cycle: Lock::new(None),
                     condvar: Condvar::new(),
-                };
-                self.latch.await(&mut waiter);
+                });
+                self.latch.await(&waiter);
 
-                match waiter.cycle {
+                match Lrc::get_mut(&mut waiter).unwrap().cycle.get_mut().take() {
                     None => Ok(()),
                     Some(cycle) => Err(cycle)
                 }
@@ -154,10 +154,10 @@ pub fn signal_complete(&self) {
 
 #[cfg(parallel_queries)]
 struct QueryWaiter<'tcx> {
-    query: *const Option<Lrc<QueryJob<'tcx>>>,
+    query: Option<Lrc<QueryJob<'tcx>>>,
     condvar: Condvar,
     span: Span,
-    cycle: Option<CycleError<'tcx>>,
+    cycle: Lock<Option<CycleError<'tcx>>>,
 }
 
 #[cfg(parallel_queries)]
@@ -171,13 +171,9 @@ fn notify(&self, registry: &rayon_core::Registry) {
 #[cfg(parallel_queries)]
 struct QueryLatchInfo<'tcx> {
     complete: bool,
-    waiters: Vec<*mut QueryWaiter<'tcx>>,
+    waiters: Vec<Lrc<QueryWaiter<'tcx>>>,
 }
 
-// Required because of raw pointers
-#[cfg(parallel_queries)]
-unsafe impl<'tcx> Send for QueryLatchInfo<'tcx> {}
-
 #[cfg(parallel_queries)]
 struct QueryLatch<'tcx> {
     info: Mutex<QueryLatchInfo<'tcx>>,
@@ -195,14 +191,14 @@ fn new() -> Self {
     }
 
     /// Awaits the caller on this latch by blocking the current thread.
-    fn await(&self, waiter: &mut QueryWaiter<'tcx>) {
+    fn await(&self, waiter: &Lrc<QueryWaiter<'tcx>>) {
         let mut info = self.info.lock();
         if !info.complete {
             // We push the waiter on to the `waiters` list. It can be accessed inside
             // the `wait` call below, by 1) the `set` method or 2) by deadlock detection.
             // Both of these will remove it from the `waiters` list before resuming
             // this thread.
-            info.waiters.push(waiter);
+            info.waiters.push(waiter.clone());
 
             // If this detects a deadlock and the deadlock handler want to resume this thread
             // we have to be in the `wait` call. This is ensured by the deadlock handler
@@ -219,9 +215,7 @@ fn set(&self) {
         info.complete = true;
         let registry = rayon_core::Registry::current();
         for waiter in info.waiters.drain(..) {
-            unsafe {
-                (*waiter).notify(&registry);
-            }
+            waiter.notify(&registry);
         }
     }
 
@@ -230,7 +224,7 @@ fn set(&self) {
     fn extract_waiter(
         &self,
         waiter: usize,
-    ) -> *mut QueryWaiter<'tcx> {
+    ) -> Lrc<QueryWaiter<'tcx>> {
         let mut info = self.info.lock();
         debug_assert!(!info.complete);
         // Remove the waiter from the list of waiters
@@ -270,13 +264,11 @@ fn visit_waiters<'tcx, F>(query_ref: Ref<'tcx>, mut visit: F) -> Option<Option<W
     }
 
     // Visit the explict waiters which use condvars and are resumable
-    for (i, &waiter) in query.latch.info.lock().waiters.iter().enumerate() {
-        unsafe {
-            if let Some(ref waiter_query) = *(*waiter).query {
-                if visit((*waiter).span, &**waiter_query as Ref).is_some() {
-                    // Return a value which indicates that this waiter can be resumed
-                    return Some(Some((query_ref, i)));
-                }
+    for (i, waiter) in query.latch.info.lock().waiters.iter().enumerate() {
+        if let Some(ref waiter_query) = waiter.query {
+            if visit(waiter.span, &**waiter_query).is_some() {
+                // Return a value which indicates that this waiter can be resumed
+                return Some(Some((query_ref, i)));
             }
         }
     }
@@ -359,7 +351,7 @@ fn connected_to_root<'tcx>(query: Ref<'tcx>, visited: &mut HashSet<Ref<'tcx>>) -
 #[cfg(parallel_queries)]
 fn remove_cycle<'tcx>(
     jobs: &mut Vec<Ref<'tcx>>,
-    wakelist: &mut Vec<*mut QueryWaiter<'tcx>>,
+    wakelist: &mut Vec<Lrc<QueryWaiter<'tcx>>>,
     tcx: TyCtxt<'_, 'tcx, '_>
 ) -> bool {
     let mut visited = HashSet::new();
@@ -439,9 +431,9 @@ fn remove_cycle<'tcx>(
         // Extract the waiter we want to resume
         let waiter = waitee_query.latch.extract_waiter(waiter_idx);
 
-        // Set the cycle error it will be picked it up when resumed
+        // Set the cycle error so it will be picked up when resumed
         unsafe {
-            (*waiter).cycle = Some(error);
+            *waiter.cycle.lock() = Some(error);
         }
 
         // Put the waiter on the list of things to resume
@@ -525,9 +517,7 @@ fn deadlock(tcx: TyCtxt<'_, '_, '_>, registry: &rayon_core::Registry) {
 
     // FIXME: Ensure this won't cause a deadlock before we return
     for waiter in wakelist.into_iter() {
-        unsafe {
-            (*waiter).notify(registry);
-        }
+        waiter.notify(registry);
     }
 
     on_panic.disable();