Avoid races in capacity accounting.

runtime/vm/pages.h

 // 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.
 
 #ifndef VM_PAGES_H_
 #define VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
+#include "vm/lockers.h"
 #include "vm/ring_buffer.h"
 #include "vm/spaces.h"
 #include "vm/virtual_memory.h"
 
 namespace dart {
 
 DECLARE_FLAG(bool, collect_code);
 DECLARE_FLAG(bool, log_code_drop);
 DECLARE_FLAG(bool, always_drop_code);
 DECLARE_FLAG(bool, write_protect_code);
@@ skipping 187 matching lines @@
     return TryAllocateInternal(
         size, type, growth_policy, is_protected, is_locked);
   }
 
   bool NeedsGarbageCollection() const {
     return page_space_controller_.NeedsGarbageCollection(usage_) ||
            NeedsExternalGC();
   }
 
   intptr_t UsedInWords() const { return usage_.used_in_words; }
-  intptr_t CapacityInWords() const { return usage_.capacity_in_words; }
+  intptr_t CapacityInWords() const {
+    MutexLocker ml(pages_lock_);
+    return usage_.capacity_in_words;
+  }
+  void IncreaseCapacityInWords(intptr_t increase_in_words) {
+     MutexLocker ml(pages_lock_);
+     IncreaseCapacityInWordsLocked(increase_in_words);
+  }
+  void IncreaseCapacityInWordsLocked(intptr_t increase_in_words) {
+    DEBUG_ASSERT(pages_lock_->Owner() == Isolate::Current());
+    usage_.capacity_in_words += increase_in_words;
+  }
   intptr_t ExternalInWords() const {
     return usage_.external_in_words;
   }
-  SpaceUsage GetCurrentUsage() const { return usage_; }
+  SpaceUsage GetCurrentUsage() const {
+    MutexLocker ml(pages_lock_);
+    return usage_;
+  }
 
   bool Contains(uword addr) const;
   bool Contains(uword addr, HeapPage::PageType type) const;
   bool IsValidAddress(uword addr) const {
     return Contains(addr);
   }
 
   void VisitObjects(ObjectVisitor* visitor) const;
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
@@ skipping 146 matching lines @@
   HeapPage* exec_pages_tail_;
   HeapPage* large_pages_;
 
   // A block of memory in a data page, managed by bump allocation. The remainder
   // is kept formatted as a FreeListElement, but is not in any freelist.
   uword bump_top_;
   uword bump_end_;
 
   // Various sizes being tracked for this generation.
   intptr_t max_capacity_in_words_;
+  // NOTE: The capacity component of usage_ is updated by the concurrent
+  // sweeper. Use (Increase)CapacityInWords(Locked) for thread-safe access.
   SpaceUsage usage_;
 
   // Keep track of running MarkSweep tasks.
   Monitor* tasks_lock_;
   intptr_t tasks_;
 
   PageSpaceController page_space_controller_;
 
   int64_t gc_time_micros_;
   intptr_t collections_;
 
   friend class ExclusivePageIterator;
   friend class PageSpaceController;
   friend class SweeperTask;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_