[m-rev.] for review: disable concurrency in non .par LLDS grades

[Julien Fischer]

For review by Peter.

-----------------------------------------------

Disable concurrency in non .par LLDS grades.

The non .par LLDS grades currently "support" concurrency. However, this support
is really on usable with a small few benchmark programs, due to the inability
of the implementation to switch threads if the executing thread blocks. Disable
this capability by causing spawn/3 to abort if used in non .par LLDS grades.

library/thread.m:
    Make the above change to spawn/3.

compiler/globals.m:
    Update the code that checks if the current grade supports concurrency.

Julien.

diff --git a/compiler/globals.m b/compiler/globals.m
index 576a3d9ff..ec1d61edf 100644
--- a/compiler/globals.m
+++ b/compiler/globals.m
@@ -1226,16 +1226,8 @@ current_grade_supports_concurrency(Globals,
ThreadsSupported) :-
     globals.get_target(Globals, Target),
     (
         Target = target_c,
-        globals.lookup_bool_option(Globals, highlevel_code, HighLevelCode),
-        % In high-level C grades we only support threads in .par grades.
-        (
-            HighLevelCode = no,
-            ThreadsSupported = yes
-        ;
-            HighLevelCode = yes,
-            globals.lookup_bool_option(Globals, parallel, Parallel),
-            ThreadsSupported = Parallel
-        )
+        globals.lookup_bool_option(Globals, parallel, Parallel),
+        ThreadsSupported = Parallel
     ;
         ( Target = target_java
         ; Target = target_csharp
diff --git a/library/thread.m b/library/thread.m
index 029742edd..0417a8368 100644
--- a/library/thread.m
+++ b/library/thread.m
@@ -251,7 +251,7 @@ can_spawn :-
     can_spawn_context,
     [will_not_call_mercury, promise_pure, thread_safe, may_not_duplicate],
 "
-#if !defined(MR_HIGHLEVEL_CODE)
+#if !defined(MR_HIGHLEVEL_CODE) && defined(MR_THREAD_SAFE)
     SUCCESS_INDICATOR = MR_TRUE;
 #else
     SUCCESS_INDICATOR = MR_FALSE;