fix and test order of TLS dtors and thread joining

Author: RalfJung

src/shims/tls.rs

@@ -328,9 +328,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     /// schedules them one by one each time it is called and reenables the
     /// thread so that it can be executed normally by the main execution loop.
     ///
-    /// FIXME: we do not support yet deallocation of thread local statics.
-    /// Issue: https://github.com/rust-lang/miri/issues/1369
-    ///
     /// Note: we consistently run TLS destructors for all threads, including the
     /// main thread. However, it is not clear that we should run the TLS
     /// destructors for the main thread. See issue:
@@ -367,6 +364,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         // All dtors done!
         this.machine.tls.delete_all_thread_tls(active_thread);
+        this.thread_terminated();
 
         Ok(())
     }

src/thread.rs

@@ -410,6 +410,20 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
         None
     }
 
+    /// Handles thread termination of the active thread: wakes up threads joining on this one,
+    /// and deallocated thread-local statics.
+    ///
+    /// This is called from `tls.rs` after handling the TLS dtors.
+    fn thread_terminated(&mut self) {
+        for (i, thread) in self.threads.iter_enumerated_mut() {
+            // Check if we need to unblock any threads.
+            if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
+                trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
+                thread.state = ThreadState::Enabled;
+            }
+        }
+    }
+
     /// Decide which action to take next and on which thread.
     ///
     /// The currently implemented scheduling policy is the one that is commonly
@@ -421,13 +435,6 @@ impl<'mir, 'tcx: 'mir> ThreadManager<'mir, 'tcx> {
         // checks whether the thread has popped all its stack and if yes, sets
         // the thread state to terminated).
         if self.threads[self.active_thread].check_terminated() {
-            // Check if we need to unblock any threads.
-            for (i, thread) in self.threads.iter_enumerated_mut() {
-                if thread.state == ThreadState::BlockedOnJoin(self.active_thread) {
-                    trace!("unblocking {:?} because {:?} terminated", i, self.active_thread);
-                    thread.state = ThreadState::Enabled;
-                }
-            }
             return Ok(SchedulingAction::ExecuteDtors);
         }
         if self.threads[MAIN_THREAD].state == ThreadState::Terminated {
@@ -660,4 +667,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
         this.machine.threads.schedule()
     }
+
+    #[inline]
+    fn thread_terminated(&mut self) {
+        self.eval_context_mut().machine.threads.thread_terminated()
+    }
 }

tests/run-pass/concurrency/tls_lib_drop.rs

@@ -9,7 +9,8 @@ struct TestCell {
 
 impl Drop for TestCell {
     fn drop(&mut self) {
-        println!("Dropping: {}", self.value.borrow())
+        for _ in 0..10 { thread::yield_now(); }
+        println!("Dropping: {} (should be before 'Continue main 1').", self.value.borrow())
     }
 }
 
@@ -28,7 +29,7 @@ fn check_destructors() {
     })
     .join()
     .unwrap();
-    println!("Continue main.")
+    println!("Continue main 1.")
 }
 
 struct JoinCell {
@@ -37,8 +38,9 @@ struct JoinCell {
 
 impl Drop for JoinCell {
     fn drop(&mut self) {
+        for _ in 0..10 { thread::yield_now(); }
         let join_handle = self.value.borrow_mut().take().unwrap();
-        println!("Joining: {}", join_handle.join().unwrap());
+        println!("Joining: {} (should be before 'Continue main 2').", join_handle.join().unwrap());
     }
 }
 

tests/run-pass/concurrency/tls_lib_drop.stdout

@@ -1,4 +1,4 @@
-Dropping: 5
-Continue main.
+Dropping: 5 (should be before 'Continue main 1').
+Continue main 1.
+Joining: 7 (should be before 'Continue main 2').
 Continue main 2.
-Joining: 7