WIP: Use new API for setting MMTk options

gc.c

@@ -1883,20 +1883,17 @@ rb_objspace_alloc(void)
     dont_gc_on();
 
 #ifdef USE_THIRD_PARTY_HEAP
-    if (!mmtk_env_plan && setenv("MMTK_PLAN", mmtk_chosen_plan, 0) != 0) {
-        fputs("[FATAL] could not set MMTK_PLAN\n", stderr);
-	    exit(EXIT_FAILURE);
-    }
+    MMTk_Options mmtk_options = mmtk_options_default();
+
+    mmtk_options_set_plan(mmtk_options, mmtk_chosen_plan);
 
     // Note: the limit is currently broken for NoGC, but we still attempt to
     // initialise it properly regardless.
     // See https://github.com/mmtk/mmtk-core/issues/214
-    mmtk_init_binding(rb_mmtk_heap_limit(), &ruby_upcalls);
+    size_t heap_size = rb_mmtk_heap_limit();
+    mmtk_options_set_heap_size(mmtk_options, heap_size);
 
-    if (!mmtk_env_plan && unsetenv("MMTK_PLAN") != 0) {
-        fputs("[FATAL] could not unset MMTK_PLAN\n", stderr);
-	    exit(EXIT_FAILURE);
-    }
+    mmtk_init_binding(mmtk_options, &ruby_upcalls);
 #endif
 
     return objspace;

mmtk.h

@@ -13,6 +13,8 @@ extern "C" {
 #define MMTK_MIN_OBJ_ALIGN 8
 #define MMTK_OBJREF_OFFSET 8
 
+typedef void* MMTk_Options;
+
 typedef void* MMTk_Mutator;
 typedef void* MMTk_TraceLocal;
 
@@ -38,10 +40,20 @@ typedef struct {
     void (*scan_object_ruby_style)(void *object);
 } RubyUpcalls;
 
+/**
+ * Options
+ */
+extern MMTk_Options mmtk_options_default();
+
+extern void mmtk_options_set_heap_size(MMTk_Options options, uintptr_t heap_size);
+
+extern void mmtk_options_set_plan(MMTk_Options options, const char *plan_name);
+
+
 /**
  * Initialization
  */
-extern void mmtk_init_binding(size_t heap_size, RubyUpcalls *ruby_upcalls);
+extern void mmtk_init_binding(MMTk_Options options, const RubyUpcalls *upcalls);
 extern void mmtk_initialize_collection(void *tls);
 extern void mmtk_enable_collection();