[sgen] Don't use workers during finishing pause if we're not parallel

Worker can be used though to drain the gray stack of workers after a forced finish (at the start of the finishing pause).

diff --git a/mono/sgen/sgen-gc.c b/mono/sgen/sgen-gc.c
index bcfee619b32c72412f15edb33a067a4ce163bdcf..08d5f45002dfbd07438171891374e2a4207b2128 100644 (file)
--- a/mono/sgen/sgen-gc.c
+++ b/mono/sgen/sgen-gc.c
@@ -1867,7 +1867,8 @@ major_copy_or_mark_from_roots (SgenGrayQueue *gc_thread_gray_queue, size_t *old_
 
        SGEN_ASSERT (0, sgen_workers_all_done (), "Why are the workers not done when we start or finish a major collection?");
        if (mode == COPY_OR_MARK_FROM_ROOTS_FINISH_CONCURRENT) {
-               sgen_workers_set_num_active_workers (0);
+               if (object_ops_par != NULL)
+                       sgen_workers_set_num_active_workers (0);
                if (sgen_workers_have_idle_work ()) {
                        /*
                         * We force the finish of the worker with the new object ops context
@@ -1912,8 +1913,11 @@ major_copy_or_mark_from_roots (SgenGrayQueue *gc_thread_gray_queue, size_t *old_
 
        if (mode == COPY_OR_MARK_FROM_ROOTS_FINISH_CONCURRENT) {
                int i, split_count = sgen_workers_get_job_split_count ();
+               gboolean parallel = object_ops_par != NULL;
 
-               gray_queue_redirect (gc_thread_gray_queue);
+               /* If we're not parallel we finish the collection on the gc thread */
+               if (parallel)
+                       gray_queue_redirect (gc_thread_gray_queue);
 
                /* Mod union card table */
                for (i = 0; i < split_count; i++) {
@@ -1921,27 +1925,29 @@ major_copy_or_mark_from_roots (SgenGrayQueue *gc_thread_gray_queue, size_t *old_
 
                        psj = (ParallelScanJob*)sgen_thread_pool_job_alloc ("scan mod union cardtable", job_scan_major_mod_union_card_table, sizeof (ParallelScanJob));
                        psj->scan_job.ops = object_ops_par ? object_ops_par : object_ops_nopar;
-                       psj->scan_job.gc_thread_gray_queue = NULL;
+                       psj->scan_job.gc_thread_gray_queue = gc_thread_gray_queue;
                        psj->job_index = i;
-                       sgen_workers_enqueue_job (&psj->scan_job.job, TRUE);
+                       sgen_workers_enqueue_job (&psj->scan_job.job, parallel);
 
                        psj = (ParallelScanJob*)sgen_thread_pool_job_alloc ("scan LOS mod union cardtable", job_scan_los_mod_union_card_table, sizeof (ParallelScanJob));
                        psj->scan_job.ops = object_ops_par ? object_ops_par : object_ops_nopar;
-                       psj->scan_job.gc_thread_gray_queue = NULL;
+                       psj->scan_job.gc_thread_gray_queue = gc_thread_gray_queue;
                        psj->job_index = i;
-                       sgen_workers_enqueue_job (&psj->scan_job.job, TRUE);
+                       sgen_workers_enqueue_job (&psj->scan_job.job, parallel);
                }
 
-               /*
-                * If we enqueue a job while workers are running we need to sgen_workers_ensure_awake
-                * in order to make sure that we are running the idle func and draining all worker
-                * gray queues. The operation of starting workers implies this, so we start them after
-                * in order to avoid doing this operation twice. The workers will drain the main gray
-                * stack that contained roots and pinned objects and also scan the mod union card
-                * table.
-                */
-               sgen_workers_start_all_workers (object_ops_nopar, object_ops_par, NULL);
-               sgen_workers_join ();
+               if (parallel) {
+                       /*
+                        * If we enqueue a job while workers are running we need to sgen_workers_ensure_awake
+                        * in order to make sure that we are running the idle func and draining all worker
+                        * gray queues. The operation of starting workers implies this, so we start them after
+                        * in order to avoid doing this operation twice. The workers will drain the main gray
+                        * stack that contained roots and pinned objects and also scan the mod union card
+                        * table.
+                        */
+                       sgen_workers_start_all_workers (object_ops_nopar, object_ops_par, NULL);
+                       sgen_workers_join ();
+               }
        }
 
        sgen_pin_stats_report ();