Merge "ART: Add comments to Scoped-/ArenaAllocator."

2 files changed, 12 insertions, 0 deletions

diff --git a/runtime/base/arena_allocator.h b/runtime/base/arena_allocator.h
index ace6c388af..36334c4129 100644
--- a/runtime/base/arena_allocator.h
+++ b/runtime/base/arena_allocator.h
@@ -288,6 +288,11 @@ class ArenaPool {
   DISALLOW_COPY_AND_ASSIGN(ArenaPool);
 };
 
+// Fast single-threaded allocator for zero-initialized memory chunks.
+//
+// Memory is allocated from ArenaPool in large chunks and then rationed through
+// the ArenaAllocator. It's returned to the ArenaPool only when the ArenaAllocator
+// is destroyed.
 class ArenaAllocator
     : private DebugStackRefCounter, private ArenaAllocatorStats, private ArenaAllocatorMemoryTool {
  public:
diff --git a/runtime/base/scoped_arena_allocator.h b/runtime/base/scoped_arena_allocator.h
index a30c73d749..a87153bd77 100644
--- a/runtime/base/scoped_arena_allocator.h
+++ b/runtime/base/scoped_arena_allocator.h
@@ -42,6 +42,7 @@ enum class ArenaFreeTag : uint8_t {
 static constexpr size_t kArenaAlignment = 8;
 
 // Holds a list of Arenas for use by ScopedArenaAllocator stack.
+// The memory is returned to the ArenaPool when the ArenaStack is destroyed.
 class ArenaStack : private DebugStackRefCounter, private ArenaAllocatorMemoryTool {
  public:
   explicit ArenaStack(ArenaPool* arena_pool);
@@ -121,6 +122,12 @@ class ArenaStack : private DebugStackRefCounter, private ArenaAllocatorMemoryToo
   DISALLOW_COPY_AND_ASSIGN(ArenaStack);
 };
 
+// Fast single-threaded allocator. Allocated chunks are _not_ guaranteed to be zero-initialized.
+//
+// Unlike the ArenaAllocator, ScopedArenaAllocator is intended for relatively short-lived
+// objects and allows nesting multiple allocators. Only the top allocator can be used but
+// once it's destroyed, its memory can be reused by the next ScopedArenaAllocator on the
+// stack. This is facilitated by returning the memory to the ArenaStack.
 class ScopedArenaAllocator
     : private DebugStackReference, private DebugStackRefCounter, private ArenaAllocatorStats {
  public: