From aa84cff4f68e09cc33129ce3fe1bad5aff19e5d9 Mon Sep 17 00:00:00 2001
From: Teo Camarasu <teofilcamarasu@gmail.com>
Date: Wed, 3 May 2023 13:52:59 +0100
Subject: rts: Ensure non-moving gc is not running when pausing

---
 rts/RtsAPI.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/rts/RtsAPI.c b/rts/RtsAPI.c
index 46cb8a91f8..1d046afbbd 100644
--- a/rts/RtsAPI.c
+++ b/rts/RtsAPI.c
@@ -19,6 +19,7 @@
 #include "StablePtr.h"
 #include "Threads.h"
 #include "Weak.h"
+#include "sm/NonMoving.h"
 
 /* ----------------------------------------------------------------------------
    Building Haskell objects from C datatypes.
@@ -709,6 +710,16 @@ Capability *pauseTokenCapability(PauseToken *pauseToken) {
 // See Note [Locking and Pausing the RTS]
 PauseToken *rts_pause (void)
 {
+
+    // Wait for any nonmoving collection to finish before pausing the RTS.
+    // The nonmoving collector needs to synchronise with the mutator,
+    // so pausing the mutator while a collection is ongoing might lead to deadlock or
+    // capabilities being prematurely re-awoken.
+    if (RtsFlags.GcFlags.useNonmoving) {
+      ACQUIRE_LOCK(&nonmoving_collection_mutex);
+    }
+
+
     // It is an error if this thread already paused the RTS. If another
     // thread has paused the RTS, then rts_pause will block until rts_resume is
     // called (and compete with other threads calling rts_pause). The blocking
@@ -771,6 +782,10 @@ void rts_resume (PauseToken *pauseToken)
     releaseAllCapabilities(getNumCapabilities(), NULL, task);
     exitMyTask();
     stgFree(pauseToken);
+
+    if (RtsFlags.GcFlags.useNonmoving) {
+      RELEASE_LOCK(&nonmoving_collection_mutex);
+    }
 }
 
 // See RtsAPI.h
-- 
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