text: //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
  //  This source code is licensed under the BSD-style license found in the
  //  LICENSE file in the root directory of this source tree. An additional grant
  //  of patent rights can be found in the PATENTS file in the same directory.
  //  This source code is also licensed under the GPLv2 license found in the
  //  COPYING file in the root directory of this source tree.
  //
  // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  // 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 <mutex>
  
  #include <rocksdb/env.h>
  #include "port/win/env_win.h"
  
  namespace rocksdb {
  namespace port {
  
  // We choose to create this on the heap and using std::once for the following
  // reasons
  // 1) Currently available MS compiler does not implement atomic C++11
  // initialization of
  //    function local statics
  // 2) We choose not to destroy the env because joining the threads from the
  // system loader
  //    which destroys the statics (same as from DLLMain) creates a system loader
  //    dead-lock.
  //    in this manner any remaining threads are terminated OK.
  namespace {
    std::once_flag winenv_once_flag;
    Env* envptr;
  };
  
  }
  
  Env* Env::Default() {
    using namespace port;
    std::call_once(winenv_once_flag, []() { envptr = new WinEnv(); });
    return envptr;
  }
  
  }
  
  