leveldb: Replace AtomicPointer with std::atomic.

This CL removes AtomicPointer from leveldb's port interface. Its usage is replaced with std::atomic<> from the C++11 standard library.

AtomicPointer was used to wrap flags, numbers, and pointers, so its instances are replaced with std::atomic<bool>, std::atomic<int>, std::atomic<size_t> and std::atomic<Node*>.

This CL does not revise the memory ordering. AtomicPointer's methods are replaced mechanically with their std::atomic equivalents, even when the underlying usage is incorrect. (Example: DBImpl::has_imm_ is written using release stores, even though it is always read using relaxed ordering.) Revising the memory ordering is left for future CLs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=237865146

6 files changed, 143 insertions, 150 deletions

diff --git a/db/db_bench.cc b/db/db_bench.cc
index 115cf45..f9403f4 100644
--- a/db/db_bench.cc
+++ b/db/db_bench.cc
@@ -34,7 +34,6 @@
 //      seekrandom    -- N random seeks
 //      open          -- cost of opening a DB
 //      crc32c        -- repeated crc32c of 4K of data
-//      acquireload   -- load N*1000 times
 //   Meta operations:
 //      compact     -- Compact the entire DB
 //      stats       -- Print DB stats
@@ -57,7 +56,6 @@ static const char* FLAGS_benchmarks =
     "crc32c,"
     "snappycomp,"
     "snappyuncomp,"
-    "acquireload,"
     ;
 
 // Number of key/values to place in database
@@ -510,8 +508,6 @@ class Benchmark {
         method = &Benchmark::Compact;
       } else if (name == Slice("crc32c")) {
         method = &Benchmark::Crc32c;
-      } else if (name == Slice("acquireload")) {
-        method = &Benchmark::AcquireLoad;
       } else if (name == Slice("snappycomp")) {
         method = &Benchmark::SnappyCompress;
       } else if (name == Slice("snappyuncomp")) {
@@ -639,22 +635,6 @@ class Benchmark {
     thread->stats.AddMessage(label);
   }
 
-  void AcquireLoad(ThreadState* thread) {
-    int dummy;
-    port::AtomicPointer ap(&dummy);
-    int count = 0;
-    void *ptr = nullptr;
-    thread->stats.AddMessage("(each op is 1000 loads)");
-    while (count < 100000) {
-      for (int i = 0; i < 1000; i++) {
-        ptr = ap.Acquire_Load();
-      }
-      count++;
-      thread->stats.FinishedSingleOp();
-    }
-    if (ptr == nullptr) exit(1); // Disable unused variable warning.
-  }
-
   void SnappyCompress(ThreadState* thread) {
     RandomGenerator gen;
     Slice input = gen.Generate(Options().block_size);
diff --git a/db/db_impl.cc b/db/db_impl.cc
index fefb883..3468862 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -8,6 +8,7 @@
 #include <stdio.h>
 
 #include <algorithm>
+#include <atomic>
 #include <set>
 #include <string>
 #include <vector>
@@ -132,10 +133,11 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
       dbname_(dbname),
       table_cache_(new TableCache(dbname_, options_, TableCacheSize(options_))),
       db_lock_(nullptr),
-      shutting_down_(nullptr),
+      shutting_down_(false),
       background_work_finished_signal_(&mutex_),
       mem_(nullptr),
       imm_(nullptr),
+      has_imm_(false),
       logfile_(nullptr),
       logfile_number_(0),
       log_(nullptr),
@@ -144,14 +146,12 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
       background_compaction_scheduled_(false),
       manual_compaction_(nullptr),
       versions_(new VersionSet(dbname_, &options_, table_cache_,
-                               &internal_comparator_)) {
-  has_imm_.Release_Store(nullptr);
-}
+                               &internal_comparator_)) {}
 
 DBImpl::~DBImpl() {
-  // Wait for background work to finish
+  // Wait for background work to finish.
   mutex_.Lock();
-  shutting_down_.Release_Store(this);  // Any non-null value is ok
+  shutting_down_.store(true, std::memory_order_release);
   while (background_compaction_scheduled_) {
     background_work_finished_signal_.Wait();
   }
@@ -547,7 +547,7 @@ void DBImpl::CompactMemTable() {
   Status s = WriteLevel0Table(imm_, &edit, base);
   base->Unref();
 
-  if (s.ok() && shutting_down_.Acquire_Load()) {
+  if (s.ok() && shutting_down_.load(std::memory_order_acquire)) {
     s = Status::IOError("Deleting DB during memtable compaction");
   }
 
@@ -562,7 +562,7 @@ void DBImpl::CompactMemTable() {
     // Commit to the new state
     imm_->Unref();
     imm_ = nullptr;
-    has_imm_.Release_Store(nullptr);
+    has_imm_.store(false, std::memory_order_release);
     DeleteObsoleteFiles();
   } else {
     RecordBackgroundError(s);
@@ -610,7 +610,8 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
   }
 
   MutexLock l(&mutex_);
-  while (!manual.done && !shutting_down_.Acquire_Load() && bg_error_.ok()) {
+  while (!manual.done && !shutting_down_.load(std::memory_order_acquire) &&
+         bg_error_.ok()) {
     if (manual_compaction_ == nullptr) {  // Idle
       manual_compaction_ = &manual;
       MaybeScheduleCompaction();
@@ -652,7 +653,7 @@ void DBImpl::MaybeScheduleCompaction() {
   mutex_.AssertHeld();
   if (background_compaction_scheduled_) {
     // Already scheduled
-  } else if (shutting_down_.Acquire_Load()) {
+  } else if (shutting_down_.load(std::memory_order_acquire)) {
     // DB is being deleted; no more background compactions
   } else if (!bg_error_.ok()) {
     // Already got an error; no more changes
@@ -673,7 +674,7 @@ void DBImpl::BGWork(void* db) {
 void DBImpl::BackgroundCall() {
   MutexLock l(&mutex_);
   assert(background_compaction_scheduled_);
-  if (shutting_down_.Acquire_Load()) {
+  if (shutting_down_.load(std::memory_order_acquire)) {
     // No more background work when shutting down.
   } else if (!bg_error_.ok()) {
     // No more background work after a background error.
@@ -752,7 +753,7 @@ void DBImpl::BackgroundCompaction() {
 
   if (status.ok()) {
     // Done
-  } else if (shutting_down_.Acquire_Load()) {
+  } else if (shutting_down_.load(std::memory_order_acquire)) {
     // Ignore compaction errors found during shutting down
   } else {
     Log(options_.info_log,
@@ -919,9 +920,9 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   std::string current_user_key;
   bool has_current_user_key = false;
   SequenceNumber last_sequence_for_key = kMaxSequenceNumber;
-  for (; input->Valid() && !shutting_down_.Acquire_Load(); ) {
+  for (; input->Valid() && !shutting_down_.load(std::memory_order_acquire); ) {
     // Prioritize immutable compaction work
-    if (has_imm_.NoBarrier_Load() != nullptr) {
+    if (has_imm_.load(std::memory_order_relaxed)) {
       const uint64_t imm_start = env_->NowMicros();
       mutex_.Lock();
       if (imm_ != nullptr) {
@@ -1014,7 +1015,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
     input->Next();
   }
 
-  if (status.ok() && shutting_down_.Acquire_Load()) {
+  if (status.ok() && shutting_down_.load(std::memory_order_acquire)) {
     status = Status::IOError("Deleting DB during compaction");
   }
   if (status.ok() && compact->builder != nullptr) {
@@ -1378,7 +1379,7 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       logfile_number_ = new_log_number;
       log_ = new log::Writer(lfile);
       imm_ = mem_;
-      has_imm_.Release_Store(imm_);
+      has_imm_.store(true, std::memory_order_release);
       mem_ = new MemTable(internal_comparator_);
       mem_->Ref();
       force = false;   // Do not force another compaction if have room
diff --git a/db/db_impl.h b/db/db_impl.h
index 00e800a..ca00d42 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -5,8 +5,11 @@
 #ifndef STORAGE_LEVELDB_DB_DB_IMPL_H_
 #define STORAGE_LEVELDB_DB_DB_IMPL_H_
 
+#include <atomic>
 #include <deque>
 #include <set>
+#include <string>
+
 #include "db/dbformat.h"
 #include "db/log_writer.h"
 #include "db/snapshot.h"
@@ -136,11 +139,11 @@ class DBImpl : public DB {
 
   // State below is protected by mutex_
   port::Mutex mutex_;
-  port::AtomicPointer shutting_down_;
+  std::atomic<bool> shutting_down_;
   port::CondVar background_work_finished_signal_ GUARDED_BY(mutex_);
   MemTable* mem_;
   MemTable* imm_ GUARDED_BY(mutex_);  // Memtable being compacted
-  port::AtomicPointer has_imm_;       // So bg thread can detect non-null imm_
+  std::atomic<bool> has_imm_;         // So bg thread can detect non-null imm_
   WritableFile* logfile_;
   uint64_t logfile_number_ GUARDED_BY(mutex_);
   log::Writer* log_;
diff --git a/db/db_test.cc b/db/db_test.cc
index 894ed23..e889a74 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
+#include <atomic>
+#include <string>
+
 #include "leveldb/db.h"
 #include "leveldb/filter_policy.h"
 #include "db/db_impl.h"
@@ -61,7 +64,7 @@ class AtomicCounter {
 void DelayMilliseconds(int millis) {
   Env::Default()->SleepForMicroseconds(millis * 1000);
 }
-}
+}  // namespace
 
 // Test Env to override default Env behavior for testing.
 class TestEnv : public EnvWrapper {
@@ -93,45 +96,45 @@ class TestEnv : public EnvWrapper {
   bool ignore_dot_files_;
 };
 
-// Special Env used to delay background operations
+// Special Env used to delay background operations.
 class SpecialEnv : public EnvWrapper {
  public:
   // sstable/log Sync() calls are blocked while this pointer is non-null.
-  port::AtomicPointer delay_data_sync_;
+  std::atomic<bool> delay_data_sync_;
 
   // sstable/log Sync() calls return an error.
-  port::AtomicPointer data_sync_error_;
+  std::atomic<bool> data_sync_error_;
 
   // Simulate no-space errors while this pointer is non-null.
-  port::AtomicPointer no_space_;
+  std::atomic<bool> no_space_;
 
   // Simulate non-writable file system while this pointer is non-null.
-  port::AtomicPointer non_writable_;
+  std::atomic<bool> non_writable_;
 
   // Force sync of manifest files to fail while this pointer is non-null.
-  port::AtomicPointer manifest_sync_error_;
+  std::atomic<bool> manifest_sync_error_;
 
   // Force write to manifest files to fail while this pointer is non-null.
-  port::AtomicPointer manifest_write_error_;
+  std::atomic<bool> manifest_write_error_;
 
   bool count_random_reads_;
   AtomicCounter random_read_counter_;
 
-  explicit SpecialEnv(Env* base) : EnvWrapper(base) {
-    delay_data_sync_.Release_Store(nullptr);
-    data_sync_error_.Release_Store(nullptr);
-    no_space_.Release_Store(nullptr);
-    non_writable_.Release_Store(nullptr);
-    count_random_reads_ = false;
-    manifest_sync_error_.Release_Store(nullptr);
-    manifest_write_error_.Release_Store(nullptr);
+  explicit SpecialEnv(Env* base) : EnvWrapper(base),
+    delay_data_sync_(false),
+    data_sync_error_(false),
+    no_space_(false),
+    non_writable_(false),
+    manifest_sync_error_(false),
+    manifest_write_error_(false),
+    count_random_reads_(false) {
   }
 
   Status NewWritableFile(const std::string& f, WritableFile** r) {
     class DataFile : public WritableFile {
      private:
-      SpecialEnv* env_;
-      WritableFile* base_;
+      SpecialEnv* const env_;
+      WritableFile* const base_;
 
      public:
       DataFile(SpecialEnv* env, WritableFile* base)
@@ -140,7 +143,7 @@ class SpecialEnv : public EnvWrapper {
       }
       ~DataFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->no_space_.Acquire_Load() != nullptr) {
+        if (env_->no_space_.load(std::memory_order_acquire)) {
           // Drop writes on the floor
           return Status::OK();
         } else {
@@ -150,10 +153,10 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->data_sync_error_.Acquire_Load() != nullptr) {
+        if (env_->data_sync_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated data sync error");
         }
-        while (env_->delay_data_sync_.Acquire_Load() != nullptr) {
+        while (env_->delay_data_sync_.load(std::memory_order_acquire)) {
           DelayMilliseconds(100);
         }
         return base_->Sync();
@@ -167,7 +170,7 @@ class SpecialEnv : public EnvWrapper {
       ManifestFile(SpecialEnv* env, WritableFile* b) : env_(env), base_(b) { }
       ~ManifestFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->manifest_write_error_.Acquire_Load() != nullptr) {
+        if (env_->manifest_write_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated writer error");
         } else {
           return base_->Append(data);
@@ -176,7 +179,7 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->manifest_sync_error_.Acquire_Load() != nullptr) {
+        if (env_->manifest_sync_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated sync error");
         } else {
           return base_->Sync();
@@ -184,7 +187,7 @@ class SpecialEnv : public EnvWrapper {
       }
     };
 
-    if (non_writable_.Acquire_Load() != nullptr) {
+    if (non_writable_.load(std::memory_order_acquire)) {
       return Status::IOError("simulated write error");
     }
 
@@ -424,7 +427,7 @@ class DBTest {
     ASSERT_TRUE(
         db_->GetProperty("leveldb.num-files-at-level" + NumberToString(level),
                          &property));
-    return atoi(property.c_str());
+    return std::stoi(property);
   }
 
   int TotalTableFiles() {
@@ -587,11 +590,13 @@ TEST(DBTest, GetFromImmutableLayer) {
     ASSERT_OK(Put("foo", "v1"));
     ASSERT_EQ("v1", Get("foo"));
 
-    env_->delay_data_sync_.Release_Store(env_);      // Block sync calls
-    Put("k1", std::string(100000, 'x'));             // Fill memtable
-    Put("k2", std::string(100000, 'y'));             // Trigger compaction
+    // Block sync calls.
+    env_->delay_data_sync_.store(true, std::memory_order_release);
+    Put("k1", std::string(100000, 'x'));             // Fill memtable.
+    Put("k2", std::string(100000, 'y'));             // Trigger compaction.
     ASSERT_EQ("v1", Get("foo"));
-    env_->delay_data_sync_.Release_Store(nullptr);   // Release sync calls
+    // Release sync calls.
+    env_->delay_data_sync_.store(false, std::memory_order_release);
   } while (ChangeOptions());
 }
 
@@ -608,7 +613,7 @@ TEST(DBTest, GetMemUsage) {
     ASSERT_OK(Put("foo", "v1"));
     std::string val;
     ASSERT_TRUE(db_->GetProperty("leveldb.approximate-memory-usage", &val));
-    int mem_usage = atoi(val.c_str());
+    int mem_usage = std::stoi(val);
     ASSERT_GT(mem_usage, 0);
     ASSERT_LT(mem_usage, 5*1024*1024);
   } while (ChangeOptions());
@@ -1106,7 +1111,7 @@ TEST(DBTest, RepeatedWritesToSameKey) {
   for (int i = 0; i < 5 * kMaxFiles; i++) {
     Put("key", value);
     ASSERT_LE(TotalTableFiles(), kMaxFiles);
-    fprintf(stderr, "after %d: %d files\n", int(i+1), TotalTableFiles());
+    fprintf(stderr, "after %d: %d files\n", i + 1, TotalTableFiles());
   }
 }
 
@@ -1271,7 +1276,7 @@ TEST(DBTest, IteratorPinsRef) {
   // Write to force compactions
   Put("foo", "newvalue1");
   for (int i = 0; i < 100; i++) {
-    ASSERT_OK(Put(Key(i), Key(i) + std::string(100000, 'v'))); // 100K values
+    ASSERT_OK(Put(Key(i), Key(i) + std::string(100000, 'v')));  // 100K values
   }
   Put("foo", "newvalue2");
 
@@ -1459,21 +1464,21 @@ TEST(DBTest, L0_CompactionBug_Issue44_a) {
 
 TEST(DBTest, L0_CompactionBug_Issue44_b) {
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
   Delete("e");
-  Put("","");
+  Put("", "");
   Reopen();
   Put("c", "cv");
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
-  Put("","");
+  Put("", "");
   DelayMilliseconds(1000);  // Wait for compaction to finish
   Reopen();
-  Put("d","dv");
+  Put("d", "dv");
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
   Delete("d");
   Delete("b");
@@ -1711,13 +1716,14 @@ TEST(DBTest, NoSpace) {
   ASSERT_EQ("v1", Get("foo"));
   Compact("a", "z");
   const int num_files = CountFiles();
-  env_->no_space_.Release_Store(env_);   // Force out-of-space errors
+  // Force out-of-space errors.
+  env_->no_space_.store(true, std::memory_order_release);
   for (int i = 0; i < 10; i++) {
     for (int level = 0; level < config::kNumLevels-1; level++) {
       dbfull()->TEST_CompactRange(level, nullptr, nullptr);
     }
   }
-  env_->no_space_.Release_Store(nullptr);
+  env_->no_space_.store(false, std::memory_order_release);
   ASSERT_LT(CountFiles(), num_files + 3);
 }
 
@@ -1727,7 +1733,8 @@ TEST(DBTest, NonWritableFileSystem) {
   options.env = env_;
   Reopen(&options);
   ASSERT_OK(Put("foo", "v1"));
-  env_->non_writable_.Release_Store(env_);  // Force errors for new files
+  // Force errors for new files.
+  env_->non_writable_.store(true, std::memory_order_release);
   std::string big(100000, 'x');
   int errors = 0;
   for (int i = 0; i < 20; i++) {
@@ -1738,7 +1745,7 @@ TEST(DBTest, NonWritableFileSystem) {
     }
   }
   ASSERT_GT(errors, 0);
-  env_->non_writable_.Release_Store(nullptr);
+  env_->non_writable_.store(false, std::memory_order_release);
 }
 
 TEST(DBTest, WriteSyncError) {
@@ -1748,7 +1755,7 @@ TEST(DBTest, WriteSyncError) {
   Options options = CurrentOptions();
   options.env = env_;
   Reopen(&options);
-  env_->data_sync_error_.Release_Store(env_);
+  env_->data_sync_error_.store(true, std::memory_order_release);
 
   // (b) Normal write should succeed
   WriteOptions w;
@@ -1762,7 +1769,7 @@ TEST(DBTest, WriteSyncError) {
   ASSERT_EQ("NOT_FOUND", Get("k2"));
 
   // (d) make sync behave normally
-  env_->data_sync_error_.Release_Store(nullptr);
+  env_->data_sync_error_.store(false, std::memory_order_release);
 
   // (e) Do a non-sync write; should fail
   w.sync = false;
@@ -1782,7 +1789,7 @@ TEST(DBTest, ManifestWriteError) {
   // We iterate twice.  In the second iteration, everything is the
   // same except the log record never makes it to the MANIFEST file.
   for (int iter = 0; iter < 2; iter++) {
-    port::AtomicPointer* error_type = (iter == 0)
+    std::atomic<bool>* error_type = (iter == 0)
         ? &env_->manifest_sync_error_
         : &env_->manifest_write_error_;
 
@@ -1802,12 +1809,12 @@ TEST(DBTest, ManifestWriteError) {
     ASSERT_EQ(NumTableFilesAtLevel(last), 1);   // foo=>bar is now in last level
 
     // Merging compaction (will fail)
-    error_type->Release_Store(env_);
+    error_type->store(true, std::memory_order_release);
     dbfull()->TEST_CompactRange(last, nullptr, nullptr);  // Should fail
     ASSERT_EQ("bar", Get("foo"));
 
     // Recovery: should not lose data
-    error_type->Release_Store(nullptr);
+    error_type->store(false, std::memory_order_release);
     Reopen(&options);
     ASSERT_EQ("bar", Get("foo"));
   }
@@ -1878,7 +1885,7 @@ TEST(DBTest, BloomFilter) {
   dbfull()->TEST_CompactMemTable();
 
   // Prevent auto compactions triggered by seeks
-  env_->delay_data_sync_.Release_Store(env_);
+  env_->delay_data_sync_.store(true, std::memory_order_release);
 
   // Lookup present keys.  Should rarely read from small sstable.
   env_->random_read_counter_.Reset();
@@ -1899,7 +1906,7 @@ TEST(DBTest, BloomFilter) {
   fprintf(stderr, "%d missing => %d reads\n", N, reads);
   ASSERT_LE(reads, 3*N/100);
 
-  env_->delay_data_sync_.Release_Store(nullptr);
+  env_->delay_data_sync_.store(false, std::memory_order_release);
   Close();
   delete options.block_cache;
   delete options.filter_policy;
@@ -1914,9 +1921,9 @@ static const int kNumKeys = 1000;
 
 struct MTState {
   DBTest* test;
-  port::AtomicPointer stop;
-  port::AtomicPointer counter[kNumThreads];
-  port::AtomicPointer thread_done[kNumThreads];
+  std::atomic<bool> stop;
+  std::atomic<int> counter[kNumThreads];
+  std::atomic<bool> thread_done[kNumThreads];
 };
 
 struct MTThread {
@@ -1928,13 +1935,13 @@ static void MTThreadBody(void* arg) {
   MTThread* t = reinterpret_cast<MTThread*>(arg);
   int id = t->id;
   DB* db = t->state->test->db_;
-  uintptr_t counter = 0;
+  int counter = 0;
   fprintf(stderr, "... starting thread %d\n", id);
   Random rnd(1000 + id);
   std::string value;
   char valbuf[1500];
-  while (t->state->stop.Acquire_Load() == nullptr) {
-    t->state->counter[id].Release_Store(reinterpret_cast<void*>(counter));
+  while (!t->state->stop.load(std::memory_order_acquire)) {
+    t->state->counter[id].store(counter, std::memory_order_release);
 
     int key = rnd.Uniform(kNumKeys);
     char keybuf[20];
@@ -1959,14 +1966,13 @@ static void MTThreadBody(void* arg) {
         ASSERT_EQ(k, key);
         ASSERT_GE(w, 0);
         ASSERT_LT(w, kNumThreads);
-        ASSERT_LE(static_cast<uintptr_t>(c), reinterpret_cast<uintptr_t>(
-            t->state->counter[w].Acquire_Load()));
+        ASSERT_LE(c, t->state->counter[w].load(std::memory_order_acquire));
       }
     }
     counter++;
   }
-  t->state->thread_done[id].Release_Store(t);
-  fprintf(stderr, "... stopping thread %d after %d ops\n", id, int(counter));
+  t->state->thread_done[id].store(true, std::memory_order_release);
+  fprintf(stderr, "... stopping thread %d after %d ops\n", id, counter);
 }
 
 }  // namespace
@@ -1976,10 +1982,10 @@ TEST(DBTest, MultiThreaded) {
     // Initialize state
     MTState mt;
     mt.test = this;
-    mt.stop.Release_Store(0);
+    mt.stop.store(false, std::memory_order_release);
     for (int id = 0; id < kNumThreads; id++) {
-      mt.counter[id].Release_Store(0);
-      mt.thread_done[id].Release_Store(0);
+      mt.counter[id].store(false, std::memory_order_release);
+      mt.thread_done[id].store(false, std::memory_order_release);
     }
 
     // Start threads
@@ -1994,9 +2000,9 @@ TEST(DBTest, MultiThreaded) {
     DelayMilliseconds(kTestSeconds * 1000);
 
     // Stop the threads and wait for them to finish
-    mt.stop.Release_Store(&mt);
+    mt.stop.store(true, std::memory_order_release);
     for (int id = 0; id < kNumThreads; id++) {
-      while (mt.thread_done[id].Acquire_Load() == nullptr) {
+      while (!mt.thread_done[id].load(std::memory_order_acquire)) {
         DelayMilliseconds(100);
       }
     }
@@ -2100,6 +2106,7 @@ class ModelDB: public DB {
     virtual Slice key() const { return iter_->first; }
     virtual Slice value() const { return iter_->second; }
     virtual Status status() const { return Status::OK(); }
+
    private:
     const KVMap* const map_;
     const bool owned_;  // Do we own map_
diff --git a/db/skiplist.h b/db/skiplist.h
index b806ce0..7ac914b 100644
--- a/db/skiplist.h
+++ b/db/skiplist.h
@@ -27,9 +27,10 @@
 //
 // ... prev vs. next pointer ordering ...
 
-#include <assert.h>
-#include <stdlib.h>
-#include "port/port.h"
+#include <atomic>
+#include <cassert>
+#include <cstdlib>
+
 #include "util/arena.h"
 #include "util/random.h"
 
@@ -105,11 +106,10 @@ class SkipList {
 
   // Modified only by Insert().  Read racily by readers, but stale
   // values are ok.
-  port::AtomicPointer max_height_;   // Height of the entire list
+  std::atomic<int> max_height_;   // Height of the entire list
 
   inline int GetMaxHeight() const {
-    return static_cast<int>(
-        reinterpret_cast<intptr_t>(max_height_.NoBarrier_Load()));
+    return max_height_.load(std::memory_order_relaxed);
   }
 
   // Read/written only by Insert().
@@ -144,7 +144,7 @@ class SkipList {
 
 // Implementation details follow
 template<typename Key, class Comparator>
-struct SkipList<Key,Comparator>::Node {
+struct SkipList<Key, Comparator>::Node {
   explicit Node(const Key& k) : key(k) { }
 
   Key const key;
@@ -155,63 +155,63 @@ struct SkipList<Key,Comparator>::Node {
     assert(n >= 0);
     // Use an 'acquire load' so that we observe a fully initialized
     // version of the returned Node.
-    return reinterpret_cast<Node*>(next_[n].Acquire_Load());
+    return next_[n].load(std::memory_order_acquire);
   }
   void SetNext(int n, Node* x) {
     assert(n >= 0);
     // Use a 'release store' so that anybody who reads through this
     // pointer observes a fully initialized version of the inserted node.
-    next_[n].Release_Store(x);
+    next_[n].store(x, std::memory_order_release);
   }
 
   // No-barrier variants that can be safely used in a few locations.
   Node* NoBarrier_Next(int n) {
     assert(n >= 0);
-    return reinterpret_cast<Node*>(next_[n].NoBarrier_Load());
+    return next_[n].load(std::memory_order_relaxed);
   }
   void NoBarrier_SetNext(int n, Node* x) {
     assert(n >= 0);
-    next_[n].NoBarrier_Store(x);
+    next_[n].store(x, std::memory_order_relaxed);
   }
 
  private:
   // Array of length equal to the node height.  next_[0] is lowest level link.
-  port::AtomicPointer next_[1];
+  std::atomic<Node*> next_[1];
 };
 
 template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node*
-SkipList<Key,Comparator>::NewNode(const Key& key, int height) {
-  char* mem = arena_->AllocateAligned(
-      sizeof(Node) + sizeof(port::AtomicPointer) * (height - 1));
-  return new (mem) Node(key);
+typename SkipList<Key, Comparator>::Node*
+SkipList<Key, Comparator>::NewNode(const Key& key, int height) {
+  char* const node_memory = arena_->AllocateAligned(
+      sizeof(Node) + sizeof(std::atomic<Node*>) * (height - 1));
+  return new (node_memory) Node(key);
 }
 
 template<typename Key, class Comparator>
-inline SkipList<Key,Comparator>::Iterator::Iterator(const SkipList* list) {
+inline SkipList<Key, Comparator>::Iterator::Iterator(const SkipList* list) {
   list_ = list;
   node_ = nullptr;
 }
 
 template<typename Key, class Comparator>
-inline bool SkipList<Key,Comparator>::Iterator::Valid() const {
+inline bool SkipList<Key, Comparator>::Iterator::Valid() const {
   return node_ != nullptr;
 }
 
 template<typename Key, class Comparator>
-inline const Key& SkipList<Key,Comparator>::Iterator::key() const {
+inline const Key& SkipList<Key, Comparator>::Iterator::key() const {
   assert(Valid());
   return node_->key;
 }
 
 template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Next() {
+inline void SkipList<Key, Comparator>::Iterator::Next() {
   assert(Valid());
   node_ = node_->Next(0);
 }
 
 template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Prev() {
+inline void SkipList<Key, Comparator>::Iterator::Prev() {
   // Instead of using explicit "prev" links, we just search for the
   // last node that falls before key.
   assert(Valid());
@@ -222,17 +222,17 @@ inline void SkipList<Key,Comparator>::Iterator::Prev() {
 }
 
 template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Seek(const Key& target) {
+inline void SkipList<Key, Comparator>::Iterator::Seek(const Key& target) {
   node_ = list_->FindGreaterOrEqual(target, nullptr);
 }
 
 template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::SeekToFirst() {
+inline void SkipList<Key, Comparator>::Iterator::SeekToFirst() {
   node_ = list_->head_->Next(0);
 }
 
 template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::SeekToLast() {
+inline void SkipList<Key, Comparator>::Iterator::SeekToLast() {
   node_ = list_->FindLast();
   if (node_ == list_->head_) {
     node_ = nullptr;
@@ -240,7 +240,7 @@ inline void SkipList<Key,Comparator>::Iterator::SeekToLast() {
 }
 
 template<typename Key, class Comparator>
-int SkipList<Key,Comparator>::RandomHeight() {
+int SkipList<Key, Comparator>::RandomHeight() {
   // Increase height with probability 1 in kBranching
   static const unsigned int kBranching = 4;
   int height = 1;
@@ -253,14 +253,15 @@ int SkipList<Key,Comparator>::RandomHeight() {
 }
 
 template<typename Key, class Comparator>
-bool SkipList<Key,Comparator>::KeyIsAfterNode(const Key& key, Node* n) const {
+bool SkipList<Key, Comparator>::KeyIsAfterNode(const Key& key, Node* n) const {
   // null n is considered infinite
   return (n != nullptr) && (compare_(n->key, key) < 0);
 }
 
 template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOrEqual(const Key& key, Node** prev)
-    const {
+typename SkipList<Key, Comparator>::Node*
+SkipList<Key, Comparator>::FindGreaterOrEqual(const Key& key,
+                                              Node** prev) const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
   while (true) {
@@ -281,8 +282,8 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOr
 }
 
 template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node*
-SkipList<Key,Comparator>::FindLessThan(const Key& key) const {
+typename SkipList<Key, Comparator>::Node*
+SkipList<Key, Comparator>::FindLessThan(const Key& key) const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
   while (true) {
@@ -302,7 +303,7 @@ SkipList<Key,Comparator>::FindLessThan(const Key& key) const {
 }
 
 template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindLast()
+typename SkipList<Key, Comparator>::Node* SkipList<Key, Comparator>::FindLast()
     const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
@@ -322,11 +323,11 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindLast()
 }
 
 template<typename Key, class Comparator>
-SkipList<Key,Comparator>::SkipList(Comparator cmp, Arena* arena)
+SkipList<Key, Comparator>::SkipList(Comparator cmp, Arena* arena)
     : compare_(cmp),
       arena_(arena),
       head_(NewNode(0 /* any key will do */, kMaxHeight)),
-      max_height_(reinterpret_cast<void*>(1)),
+      max_height_(1),
       rnd_(0xdeadbeef) {
   for (int i = 0; i < kMaxHeight; i++) {
     head_->SetNext(i, nullptr);
@@ -334,7 +335,7 @@ SkipList<Key,Comparator>::SkipList(Comparator cmp, Arena* arena)
 }
 
 template<typename Key, class Comparator>
-void SkipList<Key,Comparator>::Insert(const Key& key) {
+void SkipList<Key, Comparator>::Insert(const Key& key) {
   // TODO(opt): We can use a barrier-free variant of FindGreaterOrEqual()
   // here since Insert() is externally synchronized.
   Node* prev[kMaxHeight];
@@ -348,8 +349,6 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
     for (int i = GetMaxHeight(); i < height; i++) {
       prev[i] = head_;
     }
-    //fprintf(stderr, "Change height from %d to %d\n", max_height_, height);
-
     // It is ok to mutate max_height_ without any synchronization
     // with concurrent readers.  A concurrent reader that observes
     // the new value of max_height_ will see either the old value of
@@ -357,7 +356,7 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
     // the loop below.  In the former case the reader will
     // immediately drop to the next level since nullptr sorts after all
     // keys.  In the latter case the reader will use the new node.
-    max_height_.NoBarrier_Store(reinterpret_cast<void*>(height));
+    max_height_.store(height, std::memory_order_relaxed);
   }
 
   x = NewNode(key, height);
@@ -370,7 +369,7 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
 }
 
 template<typename Key, class Comparator>
-bool SkipList<Key,Comparator>::Contains(const Key& key) const {
+bool SkipList<Key, Comparator>::Contains(const Key& key) const {
   Node* x = FindGreaterOrEqual(key, nullptr);
   if (x != nullptr && Equal(key, x->key)) {
     return true;
diff --git a/db/skiplist_test.cc b/db/skiplist_test.cc
index 24e0887..c4cf146 100644
--- a/db/skiplist_test.cc
+++ b/db/skiplist_test.cc
@@ -3,7 +3,10 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include "db/skiplist.h"
+
+#include <atomic>
 #include <set>
+
 #include "leveldb/env.h"
 #include "port/port.h"
 #include "port/thread_annotations.h"
@@ -188,12 +191,12 @@ class ConcurrentTest {
 
   // Per-key generation
   struct State {
-    port::AtomicPointer generation[K];
-    void Set(int k, intptr_t v) {
-      generation[k].Release_Store(reinterpret_cast<void*>(v));
+    std::atomic<int> generation[K];
+    void Set(int k, int v) {
+      generation[k].store(v, std::memory_order_release);
     }
-    intptr_t Get(int k) {
-      return reinterpret_cast<intptr_t>(generation[k].Acquire_Load());
+    int Get(int k) {
+      return generation[k].load(std::memory_order_acquire);
     }
 
     State() {
@@ -300,7 +303,7 @@ class TestState {
  public:
   ConcurrentTest t_;
   int seed_;
-  port::AtomicPointer quit_flag_;
+  std::atomic<bool> quit_flag_;
 
   enum ReaderState {
     STARTING,
@@ -310,7 +313,7 @@ class TestState {
 
   explicit TestState(int s)
       : seed_(s),
-        quit_flag_(nullptr),
+        quit_flag_(false),
         state_(STARTING),
         state_cv_(&mu_) {}
 
@@ -340,7 +343,7 @@ static void ConcurrentReader(void* arg) {
   Random rnd(state->seed_);
   int64_t reads = 0;
   state->Change(TestState::RUNNING);
-  while (!state->quit_flag_.Acquire_Load()) {
+  while (!state->quit_flag_.load(std::memory_order_acquire)) {
     state->t_.ReadStep(&rnd);
     ++reads;
   }
@@ -362,7 +365,7 @@ static void RunConcurrent(int run) {
     for (int i = 0; i < kSize; i++) {
       state.t_.WriteStep(&rnd);
     }
-    state.quit_flag_.Release_Store(&state);  // Any non-null arg will do
+    state.quit_flag_.store(true, std::memory_order_release);
     state.Wait(TestState::DONE);
   }
 }