Oops, avoid deadlock.

CHANGELOG.md

@@ -18,6 +18,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   * Python backend now disables spurious NumPy overflow warnings for
     both library and binary code (#1180).
 
+  * Undid deadlocking over-synchronisation for freeing opaque objects.
+
 ## [0.18.2]
 
 ### Added

libtests/c/a.fut

@@ -2,11 +2,11 @@ type s = i32
 
 entry a (x: s) : s = x + 2
 
-type t1 = {x:i32}
+type t1 = {x:[1]i32}
 type t2 = t1
 
-entry b (x: i32) : t1 = {x=x + 3}
+entry b (x: i32) : t1 = {x=[x + 3]}
 
 entry c : t1 -> t2 = id
 
-entry d ({x}: t2) : i32 = x
+entry d ({x}: t2) : i32 = x[0]

src/Futhark/CodeGen/Backends/GenericC.hs

@@ -1053,13 +1053,14 @@ opaqueLibraryFunctions desc vds = do
     (OpaqueDecl desc)
     [C.cedecl|int $id:free_opaque($ty:ctx_ty *ctx, $ty:opaque_type *obj);|]
 
-  ops <- asks envOperations
-
+  -- We do not need to enclose the body in a critical section, because
+  -- when we free the components of the opaque, we are calling public
+  -- API functions that do their own locking.
   return
     [C.cunit|
           int $id:free_opaque($ty:ctx_ty *ctx, $ty:opaque_type *obj) {
             int ret = 0, tmp;
-            $items:(criticalSection ops free_body)
+            $items:free_body
             free(obj);
             return ret;
           }