gc: add a function to force the collector to run

This requires adding a "forced" stage for the collector,
which is the initial stage for a forced collection.
Thereafter, the collector continues to the usual stages
of collection.

gc.c

@@ -2534,6 +2534,14 @@ void gc_collector()
   ck_pr_cas_int(&gc_stage, STAGE_SWEEPING, STAGE_RESTING);
 }
 
+void gc_force(void)
+{
+ /* try to force the collector to run */
+ ck_pr_cas_int(&gc_stage, STAGE_RESTING, STAGE_FORCING);
+ /* if the collector thread was idle, then begin collecting */
+ ck_pr_cas_int(&gc_stage, STAGE_FORCING, STAGE_CLEAR_OR_MARKING);
+}
+
 void *collector_main(void *arg)
 {
   int stage;

include/cyclone/runtime.h

@@ -52,6 +52,11 @@ void GC(void *, closure, object *, int);
  */
 void gc_init_heap(long heap_size);
 
+/**
+ * \ingroup gc_force
+ */
+void gc_force(void);
+
 /**
  * \defgroup prim Primitives
  * @brief Built-in Scheme functions provided by the runtime library

include/cyclone/types.h

@@ -264,7 +264,7 @@ typedef enum { STATUS_ASYNC, STATUS_SYNC1, STATUS_SYNC2
 /** Stages of the Major GC's collector thread */
 typedef enum { STAGE_CLEAR_OR_MARKING, STAGE_TRACING
       //, STAGE_REF_PROCESSING 
-  , STAGE_SWEEPING, STAGE_RESTING
+  , STAGE_SWEEPING, STAGE_RESTING, STAGE_FORCING
 } gc_stage_type;
 
 // Constant colors are defined here.
@@ -377,6 +377,7 @@ struct gc_thread_data_t {
 
 /* GC prototypes */
 void gc_initialize(void);
+void gc_force(void);
 void gc_add_new_unrunning_mutator(gc_thread_data * thd);
 void gc_add_mutator(gc_thread_data * thd);
 void gc_remove_mutator(gc_thread_data * thd);