Detect C finalizer callbacks in rts_lock() instead of schedule()

Otherwise, finalizer callbacks cause a deadlock in the threaded RTS
(including GHCi)

1 files changed, 9 insertions, 0 deletions

diff --git a/rts/RtsAPI.c b/rts/RtsAPI.c
index 3eecab14d4..54d1e75672 100644
--- a/rts/RtsAPI.c
+++ b/rts/RtsAPI.c
@@ -16,6 +16,7 @@
 #include "Schedule.h"
 #include "Capability.h"
 #include "Stable.h"
+#include "Weak.h"
 
 /* ----------------------------------------------------------------------------
    Building Haskell objects from C datatypes.
@@ -537,6 +538,14 @@ rts_lock (void)
     Capability *cap;
     Task *task;
 
+    if (running_finalizers) {
+        errorBelch("error: a C finalizer called back into Haskell.\n"
+                   "   This was previously allowed, but is disallowed in GHC 6.10.2 and later.\n"
+                   "   To create finalizers that may call back into Haskll, use\n"
+                   "   Foreign.Concurrent.newForeignPtr instead of Foreign.newForeignPtr.");
+        stg_exit(EXIT_FAILURE);
+    }
+
     task = newBoundTask();
 
     cap = NULL;