- Fine grain locking of free list when sweeping concurrently.

runtime/vm/gc_sweeper.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/gc_sweeper.h"
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
 #include "vm/lockers.h"
 #include "vm/pages.h"
 #include "vm/thread_pool.h"
 
 namespace dart {
 
-bool GCSweeper::SweepPage(HeapPage* page, FreeList* freelist) {
+bool GCSweeper::SweepPage(HeapPage* page, FreeList* freelist, bool locked) {
   // Keep track whether this page is still in use.
   bool in_use = false;
 
   bool is_executable = (page->type() == HeapPage::kExecutable);
   uword start = page->object_start();
   uword end = page->object_end();
   uword current = start;
 
   while (current < end) {
     intptr_t obj_size;
@@ skipping 13 matching lines @@
         }
         // Expand the free block by the size of this object.
         free_end += next_obj->Size();
       }
       obj_size = free_end - current;
       if (is_executable) {
         memset(reinterpret_cast<void*>(current), 0xcc, obj_size);
       }
       if ((current != start) || (free_end != end)) {
         // Only add to the free list if not covering the whole page.
-        freelist->FreeLocked(current, obj_size);
+        if (locked) {
+          freelist->FreeLocked(current, obj_size);
+        } else {
+          freelist->Free(current, obj_size);
+        }
       }
     }
     current += obj_size;
   }
   ASSERT(current == end);
 
   return in_use;
 }
 
 
@@ skipping 44 matching lines @@
   virtual void Run() {
     Isolate::SetCurrent(task_isolate_);
     GCSweeper sweeper;
 
     HeapPage* page = first_;
     HeapPage* prev_page = NULL;
 
     while (page != NULL) {
       HeapPage* next_page = page->next();
       ASSERT(page->type() == HeapPage::kData);
-      bool page_in_use = true;
-      {
-        MutexLocker ml(freelist_->mutex());
-        page_in_use = sweeper.SweepPage(page, freelist_);
-      }
+      bool page_in_use = sweeper.SweepPage(page, freelist_, false);
       if (page_in_use) {
         prev_page = page;
       } else {
         old_space_->FreePage(page, prev_page);
       }
       {
         // Notify the mutator thread that we have added elements to the free
         // list or that more capacity is available.
         MonitorLocker ml(old_space_->tasks_lock());
         ml.Notify();
@@ skipping 27 matching lines @@
   SweeperTask* task =
       new SweeperTask(isolate->ShallowCopy(),
                       isolate->heap()->old_space(),
                       first, last,
                       freelist);
   ThreadPool* pool = Dart::thread_pool();
   pool->Run(task);
 }
 
 }  // namespace dart