From eee38b0c018b3279f77d03dff796f440f40d3516 Mon Sep 17 00:00:00 2001
From: Feng Xiao <xfxyjwf@gmail.com>
Date: Sat, 22 Aug 2015 18:25:48 -0700
Subject: Down-integrate from google3.

---
 src/google/protobuf/arena.cc | 40 +++++++++++++++++++++++-----------------
 1 file changed, 23 insertions(+), 17 deletions(-)

(limited to 'src/google/protobuf/arena.cc')

diff --git a/src/google/protobuf/arena.cc b/src/google/protobuf/arena.cc
index ed1c5ef2..907a6a20 100755
--- a/src/google/protobuf/arena.cc
+++ b/src/google/protobuf/arena.cc
@@ -66,8 +66,12 @@ void Arena::Init() {
     first_block->size = options_.initial_block_size;
     first_block->pos = kHeaderSize;
     first_block->next = NULL;
-    first_block->owner = &first_block->owner;
-    AddBlock(first_block);
+    // Thread which calls Init() owns the first block. This allows the
+    // single-threaded case to allocate on the first block without taking any
+    // locks.
+    first_block->owner = &thread_cache();
+    SetThreadCacheBlock(first_block);
+    AddBlockInternal(first_block);
     owns_first_block_ = false;
   }
 
@@ -80,7 +84,7 @@ void Arena::Init() {
 }
 
 Arena::~Arena() {
-  uint64 space_allocated = Reset();
+  uint64 space_allocated = ResetInternal();
 
   // Call the destruction hook
   if (options_.on_arena_destruction != NULL) {
@@ -89,10 +93,14 @@ Arena::~Arena() {
 }
 
 uint64 Arena::Reset() {
-  CleanupList();
-  uint64 space_allocated = FreeBlocks();
   // Invalidate any ThreadCaches pointing to any blocks we just destroyed.
   lifecycle_id_ = lifecycle_id_generator_.GetNext();
+  return ResetInternal();
+}
+
+uint64 Arena::ResetInternal() {
+  CleanupList();
+  uint64 space_allocated = FreeBlocks();
 
   // Call the reset hook
   if (options_.on_arena_reset != NULL) {
@@ -137,6 +145,10 @@ Arena::Block* Arena::NewBlock(void* me, Block* my_last_block, size_t n,
 
 void Arena::AddBlock(Block* b) {
   MutexLock l(&blocks_lock_);
+  AddBlockInternal(b);
+}
+
+void Arena::AddBlockInternal(Block* b) {
   b->next = reinterpret_cast<Block*>(google::protobuf::internal::NoBarrier_Load(&blocks_));
   google::protobuf::internal::Release_Store(&blocks_, reinterpret_cast<google::protobuf::internal::AtomicWord>(b));
   if (b->avail() != 0) {
@@ -181,16 +193,6 @@ void* Arena::AllocateAligned(const std::type_info* allocated, size_t n) {
   void* me = &thread_cache();
   Block* b = reinterpret_cast<Block*>(google::protobuf::internal::Acquire_Load(&hint_));
   if (!b || b->owner != me || b->avail() < n) {
-    // If the next block to allocate from is the first block, try to claim it
-    // for this thread.
-    if (!owns_first_block_ && b->next == NULL) {
-      MutexLock l(&blocks_lock_);
-      if (b->owner == &b->owner && b->avail() >= n) {
-        b->owner = me;
-        SetThreadCacheBlock(b);
-        return AllocFromBlock(b, n);
-      }
-    }
     return SlowAlloc(n);
   }
   return AllocFromBlock(b, n);
@@ -267,8 +269,12 @@ uint64 Arena::FreeBlocks() {
     // Make the first block that was passed in through ArenaOptions
     // available for reuse.
     first_block->pos = kHeaderSize;
-    first_block->owner = &first_block->owner;
-    AddBlock(first_block);
+    // Thread which calls Reset() owns the first block. This allows the
+    // single-threaded case to allocate on the first block without taking any
+    // locks.
+    first_block->owner = &thread_cache();
+    SetThreadCacheBlock(first_block);
+    AddBlockInternal(first_block);
   }
   return space_allocated;
 }
-- 
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