Add ASSERT_vm_locking_with_barrier

Previously we just had a comment stating that the code required a
barrier. Turns out it's not too difficult to properly assert that.

Co-authored-by: Luke Gruber <luke.gru@gmail.com>

Author: jhawthorn

concurrent_set.c

@@ -352,8 +352,7 @@ rb_concurrent_set_find_or_insert(VALUE *set_obj_ptr, VALUE key, void *data)
 VALUE
 rb_concurrent_set_delete_by_identity(VALUE set_obj, VALUE key)
 {
-    // Assume locking and barrier (which there is no assert for).
-    ASSERT_vm_locking();
+    ASSERT_vm_locking_with_barrier();
 
     struct concurrent_set *set = RTYPEDDATA_GET_DATA(set_obj);
 
@@ -391,8 +390,7 @@ rb_concurrent_set_delete_by_identity(VALUE set_obj, VALUE key)
 void
 rb_concurrent_set_foreach_with_replace(VALUE set_obj, int (*callback)(VALUE *key, void *data), void *data)
 {
-    // Assume locking and barrier (which there is no assert for).
-    ASSERT_vm_locking();
+    ASSERT_vm_locking_with_barrier();
 
     struct concurrent_set *set = RTYPEDDATA_GET_DATA(set_obj);
 

string.c

@@ -600,8 +600,7 @@ rb_obj_is_fstring_table(VALUE obj)
 void
 rb_gc_free_fstring(VALUE obj)
 {
-    // Assume locking and barrier (which there is no assert for)
-    ASSERT_vm_locking();
+    ASSERT_vm_locking_with_barrier();
 
     rb_concurrent_set_delete_by_identity(fstring_table_obj, obj);
 

vm_sync.c

@@ -25,6 +25,20 @@ RUBY_ASSERT_vm_locking(void)
     }
 }
 
+void
+RUBY_ASSERT_vm_locking_with_barrier(void)
+{
+    if (rb_multi_ractor_p()) {
+        rb_vm_t *vm = GET_VM();
+        VM_ASSERT(vm_locked(vm));
+
+        if (vm->ractor.cnt > 1) {
+            /* Written to only when holding both ractor.sync and ractor.sched lock */
+            VM_ASSERT(vm->ractor.sched.barrier_waiting);
+        }
+    }
+}
+
 void
 RUBY_ASSERT_vm_unlocking(void)
 {

vm_sync.h

@@ -142,11 +142,14 @@ rb_vm_lock_leave_cr(struct rb_ractor_struct *cr, unsigned int *levp, const char
 
 #if RUBY_DEBUG > 0
 void RUBY_ASSERT_vm_locking(void);
+void RUBY_ASSERT_vm_locking_with_barrier(void);
 void RUBY_ASSERT_vm_unlocking(void);
 #define ASSERT_vm_locking() RUBY_ASSERT_vm_locking()
+#define ASSERT_vm_locking_with_barrier() RUBY_ASSERT_vm_locking_with_barrier()
 #define ASSERT_vm_unlocking() RUBY_ASSERT_vm_unlocking()
 #else
 #define ASSERT_vm_locking()
+#define ASSERT_vm_locking_with_barrier()
 #define ASSERT_vm_unlocking()
 #endif