Refine GC_parallel documentation in gc.h

* include/gc.h [GC_THREADS] (GC_parallel): Refine comment about the
case when it is non-zero.

diff --git a/include/gc.h b/include/gc.h
index c7d84e3..0778ad9 100644 (file)
--- a/include/gc.h
+++ b/include/gc.h
@@ -89,11 +89,12 @@ GC_API GC_word GC_CALL GC_get_gc_no(void);
 #ifdef GC_THREADS
   GC_API GC_ATTR_DEPRECATED int GC_parallel;
                         /* GC is parallelized for performance on        */
-                        /* multiprocessors.  Currently set only         */
-                        /* implicitly if collector is built with        */
-                        /* PARALLEL_MARK defined and if either:         */
-                        /*  Env variable GC_NPROCS is set to > 1, or    */
-                        /*  GC_NPROCS is not set and this is an MP.     */
+                        /* multiprocessors.  Set to a non-zero value    */
+                        /* only implicitly if collector is built with   */
+                        /* PARALLEL_MARK defined, and if either         */
+                        /* GC_MARKERS (or GC_NPROCS) environment        */
+                        /* variable is set to > 1, or multiple cores    */
+                        /* (processors) are available.                  */
                         /* If GC_parallel is on (non-zero), incremental */
                         /* collection is only partially functional,     */
                         /* and may not be desirable.  The getter does   */