ntdll: Try to merge threadpool wait queue buckets if possible.

When the number of elements per bucket is too small, then try to reduce the number of threads by merging buckets. This is to ensure that the number of running wait queue threads doesn't get too big.

ntdll: Try to merge threadpool wait queue buckets if possible.
00215697 · Sebastian Lackner · Alexandre Julliard · 634bbed3 · 00215697
Commit 00215697 authored Jul 05, 2015 by Sebastian Lackner Committed by Alexandre Julliard Jul 06, 2015
Hide whitespace changes
Inline Side-by-side

Showing with 40 additions and 0 deletions

threadpool.c dlls/ntdll/threadpool.c +40 -0

No files found.
--- a/dlls/ntdll/threadpool.c
+++ b/dlls/ntdll/threadpool.c
@@ -1528,6 +1528,46 @@ static void CALLBACK waitqueue_thread_proc( void *param )
                tp_object_release( wait );
            }
        }
+
+        /* Try to merge bucket with other threads. */
+        if (waitqueue.num_buckets > 1 && bucket->objcount &&
+            bucket->objcount <= MAXIMUM_WAITQUEUE_OBJECTS * 1 / 3)
+        {
+            struct waitqueue_bucket *other_bucket;
+            LIST_FOR_EACH_ENTRY( other_bucket, &waitqueue.buckets, struct waitqueue_bucket, bucket_entry )
+            {
+                if (other_bucket != bucket && other_bucket->objcount &&
+                    other_bucket->objcount + bucket->objcount <= MAXIMUM_WAITQUEUE_OBJECTS * 2 / 3)
+                {
+                    other_bucket->objcount += bucket->objcount;
+                    bucket->objcount = 0;
+
+                    /* Update reserved list. */
+                    LIST_FOR_EACH_ENTRY( wait, &bucket->reserved, struct threadpool_object, u.wait.wait_entry )
+                    {
+                        assert( wait->type == TP_OBJECT_TYPE_WAIT );
+                        wait->u.wait.bucket = other_bucket;
+                    }
+                    list_move_tail( &other_bucket->reserved, &bucket->reserved );
+
+                    /* Update waiting list. */
+                    LIST_FOR_EACH_ENTRY( wait, &bucket->waiting, struct threadpool_object, u.wait.wait_entry )
+                    {
+                        assert( wait->type == TP_OBJECT_TYPE_WAIT );
+                        wait->u.wait.bucket = other_bucket;
+                    }
+                    list_move_tail( &other_bucket->waiting, &bucket->waiting );
+
+                    /* Move bucket to the end, to keep the probability of
+                     * newly added wait objects as small as possible. */
+                    list_remove( &bucket->bucket_entry );
+                    list_add_tail( &waitqueue.buckets, &bucket->bucket_entry );
+
+                    NtSetEvent( other_bucket->update_event, NULL );
+                    break;
+                }
+            }
+        }
    }

    /* Remove this bucket from the list. */