rocksdb/port/win/env_win.cc

//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
//
// 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 "port/win/env_win.h"
#include "port/win/win_thread.h"
#include <algorithm>
#include <ctime>
#include <thread>

#include <errno.h>
#include <process.h> // _getpid
#include <io.h> // _access
#include <direct.h> // _rmdir, _mkdir, _getcwd
#include <sys/types.h>
#include <sys/stat.h>

#include "rocksdb/env.h"
#include "rocksdb/slice.h"

#include "port/port.h"
#include "port/dirent.h"
#include "port/win/win_logger.h"
#include "port/win/io_win.h"

#include "monitoring/iostats_context_imp.h"

#include "monitoring/thread_status_updater.h"
#include "monitoring/thread_status_util.h"

#include <rpc.h>  // for uuid generation
#include <windows.h>

namespace rocksdb {

ThreadStatusUpdater* CreateThreadStatusUpdater() {
  return new ThreadStatusUpdater();
}

namespace {

// RAII helpers for HANDLEs
const auto CloseHandleFunc = [](HANDLE h) { ::CloseHandle(h); };
typedef std::unique_ptr<void, decltype(CloseHandleFunc)> UniqueCloseHandlePtr;

void WinthreadCall(const char* label, std::error_code result) {
  if (0 != result.value()) {
    fprintf(stderr, "pthread %s: %s\n", label, strerror(result.value()));
    abort();
  }
}

}

namespace port {

WinEnvIO::WinEnvIO(Env* hosted_env)
  :   hosted_env_(hosted_env),
      page_size_(4 * 1012),
      allocation_granularity_(page_size_),
      perf_counter_frequency_(0),
      GetSystemTimePreciseAsFileTime_(NULL) {

  SYSTEM_INFO sinfo;
  GetSystemInfo(&sinfo);

  page_size_ = sinfo.dwPageSize;
  allocation_granularity_ = sinfo.dwAllocationGranularity;

  {
    LARGE_INTEGER qpf;
    // No init as the compiler complains about unused var
    BOOL ret;
    ret = QueryPerformanceFrequency(&qpf);
    assert(ret == TRUE);
    perf_counter_frequency_ = qpf.QuadPart;
  }

  HMODULE module = GetModuleHandle("kernel32.dll");
  if (module != NULL) {
    GetSystemTimePreciseAsFileTime_ = (FnGetSystemTimePreciseAsFileTime)GetProcAddress(
      module, "GetSystemTimePreciseAsFileTime");
  }
}

WinEnvIO::~WinEnvIO() {
}

Status WinEnvIO::DeleteFile(const std::string& fname) {
  Status result;

  if (_unlink(fname.c_str())) {
    result = IOError("Failed to delete: " + fname, errno);
  }

  return result;
}

Status WinEnvIO::GetCurrentTime(int64_t* unix_time) {
  time_t time = std::time(nullptr);
  if (time == (time_t)(-1)) {
    return Status::NotSupported("Failed to get time");
  }

  *unix_time = time;
  return Status::OK();
}

Status WinEnvIO::NewSequentialFile(const std::string& fname,
  std::unique_ptr<SequentialFile>* result,
  const EnvOptions& options) {
  Status s;

  result->reset();

  // Corruption test needs to rename and delete files of these kind
  // while they are still open with another handle. For that reason we
  // allow share_write and delete(allows rename).
  HANDLE hFile = INVALID_HANDLE_VALUE;

  DWORD fileFlags = FILE_ATTRIBUTE_READONLY;

  if (options.use_direct_reads && !options.use_mmap_reads) {
    fileFlags |= FILE_FLAG_NO_BUFFERING;
  }

  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile = CreateFileA(
      fname.c_str(), GENERIC_READ,
      FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
      OPEN_EXISTING,  // Original fopen mode is "rb"
      fileFlags, NULL);
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    s = IOErrorFromWindowsError("Failed to open NewSequentialFile" + fname,
      lastError);
  } else {
    result->reset(new WinSequentialFile(fname, hFile, options));
  }
  return s;
}

Status WinEnvIO::NewRandomAccessFile(const std::string& fname,
  std::unique_ptr<RandomAccessFile>* result,
  const EnvOptions& options) {
  result->reset();
  Status s;

  // Open the file for read-only random access
  // Random access is to disable read-ahead as the system reads too much data
  DWORD fileFlags = FILE_ATTRIBUTE_READONLY;

  if (options.use_direct_reads && !options.use_mmap_reads) {
    fileFlags |= FILE_FLAG_NO_BUFFERING;
  } else {
    fileFlags |= FILE_FLAG_RANDOM_ACCESS;
  }

  /// Shared access is necessary for corruption test to pass
  // almost all tests would work with a possible exception of fault_injection
  HANDLE hFile = 0;
  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile =
      CreateFileA(fname.c_str(), GENERIC_READ,
      FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
      NULL, OPEN_EXISTING, fileFlags, NULL);
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    return IOErrorFromWindowsError(
      "NewRandomAccessFile failed to Create/Open: " + fname, lastError);
  }

  UniqueCloseHandlePtr fileGuard(hFile, CloseHandleFunc);

  // CAUTION! This will map the entire file into the process address space
  if (options.use_mmap_reads && sizeof(void*) >= 8) {
    // Use mmap when virtual address-space is plentiful.
    uint64_t fileSize;

    s = GetFileSize(fname, &fileSize);

    if (s.ok()) {
      // Will not map empty files
      if (fileSize == 0) {
        return IOError(
          "NewRandomAccessFile failed to map empty file: " + fname, EINVAL);
      }

      HANDLE hMap = CreateFileMappingA(hFile, NULL, PAGE_READONLY,
        0,  // Whole file at its present length
        0,
        NULL);  // Mapping name

      if (!hMap) {
        auto lastError = GetLastError();
        return IOErrorFromWindowsError(
          "Failed to create file mapping for NewRandomAccessFile: " + fname,
          lastError);
      }

      UniqueCloseHandlePtr mapGuard(hMap, CloseHandleFunc);

      const void* mapped_region =
        MapViewOfFileEx(hMap, FILE_MAP_READ,
        0,  // High DWORD of access start
        0,  // Low DWORD
        fileSize,
        NULL);  // Let the OS choose the mapping

      if (!mapped_region) {
        auto lastError = GetLastError();
        return IOErrorFromWindowsError(
          "Failed to MapViewOfFile for NewRandomAccessFile: " + fname,
          lastError);
      }

      result->reset(new WinMmapReadableFile(fname, hFile, hMap, mapped_region,
        fileSize));

      mapGuard.release();
      fileGuard.release();
    }
  } else {
    result->reset(new WinRandomAccessFile(fname, hFile, page_size_, options));
    fileGuard.release();
  }
  return s;
}

Status WinEnvIO::OpenWritableFile(const std::string& fname,
  std::unique_ptr<WritableFile>* result,
  const EnvOptions& options,
  bool reopen) {

  const size_t c_BufferCapacity = 64 * 1024;

  EnvOptions local_options(options);

  result->reset();
  Status s;

  DWORD fileFlags = FILE_ATTRIBUTE_NORMAL;

  if (local_options.use_direct_writes && !local_options.use_mmap_writes) {
    fileFlags = FILE_FLAG_NO_BUFFERING;
  }

  // Desired access. We are want to write only here but if we want to memory
  // map
  // the file then there is no write only mode so we have to create it
  // Read/Write
  // However, MapViewOfFile specifies only Write only
  DWORD desired_access = GENERIC_WRITE;
  DWORD shared_mode = FILE_SHARE_READ;

  if (local_options.use_mmap_writes) {
    desired_access |= GENERIC_READ;
  }
  else {
    // Adding this solely for tests to pass (fault_injection_test,
    // wal_manager_test).
    shared_mode |= (FILE_SHARE_WRITE | FILE_SHARE_DELETE);
  }

  // This will always truncate the file
  DWORD creation_disposition = CREATE_ALWAYS;
  if (reopen) {
    creation_disposition = OPEN_ALWAYS;
  }

  HANDLE hFile = 0;
  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile = CreateFileA(
      fname.c_str(),
      desired_access,  // Access desired
      shared_mode,
      NULL,           // Security attributes
      creation_disposition,  // Posix env says (reopen) ? (O_CREATE | O_APPEND) : O_CREAT | O_TRUNC
      fileFlags,      // Flags
      NULL);          // Template File
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    return IOErrorFromWindowsError(
      "Failed to create a NewWriteableFile: " + fname, lastError);
  }

  // We will start writing at the end, appending
  if (reopen) {
    LARGE_INTEGER zero_move;
    zero_move.QuadPart = 0;
    BOOL ret = SetFilePointerEx(hFile, zero_move, NULL, FILE_END);
    if (!ret) {
      auto lastError = GetLastError();
      return IOErrorFromWindowsError(
        "Failed to create a ReopenWritableFile move to the end: " + fname, lastError);
    }
  }

  if (options.use_mmap_writes) {
    // We usually do not use mmmapping on SSD and thus we pass memory
    // page_size
    result->reset(new WinMmapFile(fname, hFile, page_size_,
      allocation_granularity_, local_options));
  } else {
    // Here we want the buffer allocation to be aligned by the SSD page size
    // and to be a multiple of it
    result->reset(new WinWritableFile(fname, hFile, page_size_,
      c_BufferCapacity, local_options));
  }
  return s;
}

Status WinEnvIO::NewRandomRWFile(const std::string & fname,
  std::unique_ptr<RandomRWFile>* result, const EnvOptions & options) {

  Status s;

  // Open the file for read-only random access
  // Random access is to disable read-ahead as the system reads too much data
  DWORD desired_access = GENERIC_READ | GENERIC_WRITE;
  DWORD shared_mode = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
  DWORD creation_disposition = OPEN_ALWAYS; // Create if necessary or open existing
  DWORD file_flags = FILE_FLAG_RANDOM_ACCESS;

  if (options.use_direct_reads && options.use_direct_writes) {
    file_flags |= FILE_FLAG_NO_BUFFERING;
  }

  /// Shared access is necessary for corruption test to pass
  // almost all tests would work with a possible exception of fault_injection
  HANDLE hFile = 0;
  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile =
      CreateFileA(fname.c_str(),
        desired_access,
        shared_mode,
        NULL, // Security attributes
        creation_disposition,
        file_flags,
        NULL);
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    return IOErrorFromWindowsError(
      "NewRandomRWFile failed to Create/Open: " + fname, lastError);
  }

  UniqueCloseHandlePtr fileGuard(hFile, CloseHandleFunc);
  result->reset(new WinRandomRWFile(fname, hFile, page_size_, options));
  fileGuard.release();

  return s;
}

Status WinEnvIO::NewDirectory(const std::string& name,
  std::unique_ptr<Directory>* result) {
  Status s;
  // Must be nullptr on failure
  result->reset();
  // Must fail if directory does not exist
  if (!DirExists(name)) {
    s = IOError("Directory does not exist: " + name, EEXIST);
  } else {
    IOSTATS_TIMER_GUARD(open_nanos);
    result->reset(new WinDirectory);
  }
  return s;
}

Status WinEnvIO::FileExists(const std::string& fname) {
  // F_OK == 0
  const int F_OK_ = 0;
  return _access(fname.c_str(), F_OK_) == 0 ? Status::OK()
    : Status::NotFound();
}

Status WinEnvIO::GetChildren(const std::string& dir,
  std::vector<std::string>* result) {

  result->clear();
  std::vector<std::string> output;

  Status status;

  auto CloseDir = [](DIR* p) { closedir(p); };
  std::unique_ptr<DIR, decltype(CloseDir)> dirp(opendir(dir.c_str()),
    CloseDir);

  if (!dirp) {
    switch (errno) {
      case EACCES:
      case ENOENT:
      case ENOTDIR:
        return Status::NotFound();
      default:
        return IOError(dir, errno);
    }
  } else {
    if (result->capacity() > 0) {
      output.reserve(result->capacity());
    }

    struct dirent* ent = readdir(dirp.get());
    while (ent) {
      output.push_back(ent->d_name);
      ent = readdir(dirp.get());
    }
  }

  output.swap(*result);

  return status;
}

Status WinEnvIO::CreateDir(const std::string& name) {
  Status result;

  if (_mkdir(name.c_str()) != 0) {
    auto code = errno;
    result = IOError("Failed to create dir: " + name, code);
  }

  return result;
}

Status  WinEnvIO::CreateDirIfMissing(const std::string& name) {
  Status result;

  if (DirExists(name)) {
    return result;
  }

  if (_mkdir(name.c_str()) != 0) {
    if (errno == EEXIST) {
      result =
        Status::IOError("`" + name + "' exists but is not a directory");
    } else {
      auto code = errno;
      result = IOError("Failed to create dir: " + name, code);
    }
  }

  return result;
}

Status WinEnvIO::DeleteDir(const std::string& name) {
  Status result;
  if (_rmdir(name.c_str()) != 0) {
    auto code = errno;
    result = IOError("Failed to remove dir: " + name, code);
  }
  return result;
}

Status WinEnvIO::GetFileSize(const std::string& fname,
  uint64_t* size) {
  Status s;

  WIN32_FILE_ATTRIBUTE_DATA attrs;
  if (GetFileAttributesExA(fname.c_str(), GetFileExInfoStandard, &attrs)) {
    ULARGE_INTEGER file_size;
    file_size.HighPart = attrs.nFileSizeHigh;
    file_size.LowPart = attrs.nFileSizeLow;
    *size = file_size.QuadPart;
  } else {
    auto lastError = GetLastError();
    s = IOErrorFromWindowsError("Can not get size for: " + fname, lastError);
  }
  return s;
}

uint64_t WinEnvIO::FileTimeToUnixTime(const FILETIME& ftTime) {
  const uint64_t c_FileTimePerSecond = 10000000U;
  // UNIX epoch starts on 1970-01-01T00:00:00Z
  // Windows FILETIME starts on 1601-01-01T00:00:00Z
  // Therefore, we need to subtract the below number of seconds from
  // the seconds that we obtain from FILETIME with an obvious loss of
  // precision
  const uint64_t c_SecondBeforeUnixEpoch = 11644473600U;

  ULARGE_INTEGER li;
  li.HighPart = ftTime.dwHighDateTime;
  li.LowPart = ftTime.dwLowDateTime;

  uint64_t result =
    (li.QuadPart / c_FileTimePerSecond) - c_SecondBeforeUnixEpoch;
  return result;
}

Status WinEnvIO::GetFileModificationTime(const std::string& fname,
  uint64_t* file_mtime) {
  Status s;

  WIN32_FILE_ATTRIBUTE_DATA attrs;
  if (GetFileAttributesExA(fname.c_str(), GetFileExInfoStandard, &attrs)) {
    *file_mtime = FileTimeToUnixTime(attrs.ftLastWriteTime);
  } else {
    auto lastError = GetLastError();
    s = IOErrorFromWindowsError(
      "Can not get file modification time for: " + fname, lastError);
    *file_mtime = 0;
  }

  return s;
}

Status WinEnvIO::RenameFile(const std::string& src,
  const std::string& target) {
  Status result;

  // rename() is not capable of replacing the existing file as on Linux
  // so use OS API directly
  if (!MoveFileExA(src.c_str(), target.c_str(), MOVEFILE_REPLACE_EXISTING)) {
    DWORD lastError = GetLastError();

    std::string text("Failed to rename: ");
    text.append(src).append(" to: ").append(target);

    result = IOErrorFromWindowsError(text, lastError);
  }

  return result;
}

Status WinEnvIO::LinkFile(const std::string& src,
  const std::string& target) {
  Status result;

  if (!CreateHardLinkA(target.c_str(), src.c_str(), NULL)) {
    DWORD lastError = GetLastError();

    std::string text("Failed to link: ");
    text.append(src).append(" to: ").append(target);

    result = IOErrorFromWindowsError(text, lastError);
  }

  return result;
}

Status  WinEnvIO::LockFile(const std::string& lockFname,
  FileLock** lock) {
  assert(lock != nullptr);

  *lock = NULL;
  Status result;

  // No-sharing, this is a LOCK file
  const DWORD ExclusiveAccessON = 0;

  // Obtain exclusive access to the LOCK file
  // Previously, instead of NORMAL attr we set DELETE on close and that worked
  // well except with fault_injection test that insists on deleting it.
  HANDLE hFile = 0;
  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile = CreateFileA(lockFname.c_str(), (GENERIC_READ | GENERIC_WRITE),
      ExclusiveAccessON, NULL, CREATE_ALWAYS,
      FILE_ATTRIBUTE_NORMAL, NULL);
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    result = IOErrorFromWindowsError(
      "Failed to create lock file: " + lockFname, lastError);
  } else {
    *lock = new WinFileLock(hFile);
  }

  return result;
}

Status WinEnvIO::UnlockFile(FileLock* lock) {
  Status result;

  assert(lock != nullptr);

  delete lock;

  return result;
}

Status WinEnvIO::GetTestDirectory(std::string* result) {
  std::string output;

  const char* env = getenv("TEST_TMPDIR");
  if (env && env[0] != '\0') {
    output = env;
    CreateDir(output);
  } else {
    env = getenv("TMP");

    if (env && env[0] != '\0') {
      output = env;
    } else {
      output = "c:\\tmp";
    }

    CreateDir(output);
  }

  output.append("\\testrocksdb-");
  output.append(std::to_string(_getpid()));

  CreateDir(output);

  output.swap(*result);

  return Status::OK();
}

Status WinEnvIO::NewLogger(const std::string& fname,
  std::shared_ptr<Logger>* result) {
  Status s;

  result->reset();

  HANDLE hFile = 0;
  {
    IOSTATS_TIMER_GUARD(open_nanos);
    hFile = CreateFileA(
      fname.c_str(), GENERIC_WRITE,
      FILE_SHARE_READ | FILE_SHARE_DELETE,  // In RocksDb log files are
      // renamed and deleted before
      // they are closed. This enables
      // doing so.
      NULL,
      CREATE_ALWAYS,  // Original fopen mode is "w"
      FILE_ATTRIBUTE_NORMAL, NULL);
  }

  if (INVALID_HANDLE_VALUE == hFile) {
    auto lastError = GetLastError();
    s = IOErrorFromWindowsError("Failed to open LogFile" + fname, lastError);
  } else {
    {
      // With log files we want to set the true creation time as of now
      // because the system
      // for some reason caches the attributes of the previous file that just
      // been renamed from
      // this name so auto_roll_logger_test fails
      FILETIME ft;
      GetSystemTimeAsFileTime(&ft);
      // Set creation, last access and last write time to the same value
      SetFileTime(hFile, &ft, &ft, &ft);
    }
    result->reset(new WinLogger(&WinEnvThreads::gettid, hosted_env_, hFile));
  }
  return s;
}

uint64_t WinEnvIO::NowMicros() {

  if (GetSystemTimePreciseAsFileTime_ != NULL) {
    // all std::chrono clocks on windows proved to return
    // values that may repeat that is not good enough for some uses.
    const int64_t c_UnixEpochStartTicks = 116444736000000000LL;
    const int64_t c_FtToMicroSec = 10;

    // This interface needs to return system time and not
    // just any microseconds because it is often used as an argument
    // to TimedWait() on condition variable
    FILETIME ftSystemTime;
    GetSystemTimePreciseAsFileTime_(&ftSystemTime);

    LARGE_INTEGER li;
    li.LowPart = ftSystemTime.dwLowDateTime;
    li.HighPart = ftSystemTime.dwHighDateTime;
    // Subtract unix epoch start
    li.QuadPart -= c_UnixEpochStartTicks;
    // Convert to microsecs
    li.QuadPart /= c_FtToMicroSec;
    return li.QuadPart;
  }
  using namespace std::chrono;
  return duration_cast<microseconds>(system_clock::now().time_since_epoch()).count();
}

uint64_t WinEnvIO::NowNanos() {
  // all std::chrono clocks on windows have the same resolution that is only
  // good enough for microseconds but not nanoseconds
  // On Windows 8 and Windows 2012 Server
  // GetSystemTimePreciseAsFileTime(&current_time) can be used
  LARGE_INTEGER li;
  QueryPerformanceCounter(&li);
  // Convert to nanoseconds first to avoid loss of precision
  // and divide by frequency
  li.QuadPart *= std::nano::den;
  li.QuadPart /= perf_counter_frequency_;
  return li.QuadPart;
}

Status WinEnvIO::GetHostName(char* name, uint64_t len) {
  Status s;
  DWORD nSize = static_cast<DWORD>(
    std::min<uint64_t>(len, std::numeric_limits<DWORD>::max()));

  if (!::GetComputerNameA(name, &nSize)) {
    auto lastError = GetLastError();
    s = IOErrorFromWindowsError("GetHostName", lastError);
  } else {
    name[nSize] = 0;
  }

  return s;
}

Status WinEnvIO::GetAbsolutePath(const std::string& db_path,
  std::string* output_path) {
  // Check if we already have an absolute path
  // that starts with non dot and has a semicolon in it
  if ((!db_path.empty() && (db_path[0] == '/' || db_path[0] == '\\')) ||
    (db_path.size() > 2 && db_path[0] != '.' &&
    ((db_path[1] == ':' && db_path[2] == '\\') ||
    (db_path[1] == ':' && db_path[2] == '/')))) {
    *output_path = db_path;
    return Status::OK();
  }

  std::string result;
  result.resize(_MAX_PATH);

  char* ret = _getcwd(&result[0], _MAX_PATH);
  if (ret == nullptr) {
    return Status::IOError("Failed to get current working directory",
      strerror(errno));
  }

  result.resize(strlen(result.data()));

  result.swap(*output_path);
  return Status::OK();
}

std::string WinEnvIO::TimeToString(uint64_t secondsSince1970) {
  std::string result;

  const time_t seconds = secondsSince1970;
  const int maxsize = 64;

  struct tm t;
  errno_t ret = localtime_s(&t, &seconds);

  if (ret) {
    result = std::to_string(seconds);
  } else {
    result.resize(maxsize);
    char* p = &result[0];

    int len = snprintf(p, maxsize, "%04d/%02d/%02d-%02d:%02d:%02d ",
      t.tm_year + 1900, t.tm_mon + 1, t.tm_mday, t.tm_hour,
      t.tm_min, t.tm_sec);
    assert(len > 0);

    result.resize(len);
  }

  return result;
}

EnvOptions WinEnvIO::OptimizeForLogWrite(const EnvOptions& env_options,
  const DBOptions& db_options) const {
  EnvOptions optimized = env_options;
  optimized.bytes_per_sync = db_options.wal_bytes_per_sync;
  optimized.use_mmap_writes = false;
  // This is because we flush only whole pages on unbuffered io and
  // the last records are not guaranteed to be flushed.
  optimized.use_direct_writes = false;
  // TODO(icanadi) it's faster if fallocate_with_keep_size is false, but it
  // breaks TransactionLogIteratorStallAtLastRecord unit test. Fix the unit
  // test and make this false
  optimized.fallocate_with_keep_size = true;
  return optimized;
}

EnvOptions WinEnvIO::OptimizeForManifestWrite(
  const EnvOptions& env_options) const {
  EnvOptions optimized = env_options;
  optimized.use_mmap_writes = false;
  optimized.use_direct_writes = false;
  optimized.fallocate_with_keep_size = true;
  return optimized;
}

// Returns true iff the named directory exists and is a directory.
bool WinEnvIO::DirExists(const std::string& dname) {
  WIN32_FILE_ATTRIBUTE_DATA attrs;
  if (GetFileAttributesExA(dname.c_str(), GetFileExInfoStandard, &attrs)) {
    return 0 != (attrs.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY);
  }
  return false;
}

////////////////////////////////////////////////////////////////////////
// WinEnvThreads

WinEnvThreads::WinEnvThreads(Env* hosted_env) : hosted_env_(hosted_env), thread_pools_(Env::Priority::TOTAL) {

  for (int pool_id = 0; pool_id < Env::Priority::TOTAL; ++pool_id) {
    thread_pools_[pool_id].SetThreadPriority(
      static_cast<Env::Priority>(pool_id));
    // This allows later initializing the thread-local-env of each thread.
    thread_pools_[pool_id].SetHostEnv(hosted_env);
  }
}

WinEnvThreads::~WinEnvThreads() {

  WaitForJoin();

  for (auto& thpool : thread_pools_) {
    thpool.JoinAllThreads();
  }
}

void WinEnvThreads::Schedule(void(*function)(void*), void* arg, Env::Priority pri,
  void* tag, void(*unschedFunction)(void* arg)) {
  assert(pri >= Env::Priority::BOTTOM && pri <= Env::Priority::HIGH);
  thread_pools_[pri].Schedule(function, arg, tag, unschedFunction);
}

int WinEnvThreads::UnSchedule(void* arg, Env::Priority pri) {
  return thread_pools_[pri].UnSchedule(arg);
}

namespace {

  struct StartThreadState {
    void(*user_function)(void*);
    void* arg;
  };

  void* StartThreadWrapper(void* arg) {
    std::unique_ptr<StartThreadState> state(
      reinterpret_cast<StartThreadState*>(arg));
    state->user_function(state->arg);
    return nullptr;
  }

}

void WinEnvThreads::StartThread(void(*function)(void* arg), void* arg) {
  std::unique_ptr<StartThreadState> state(new StartThreadState);
  state->user_function = function;
  state->arg = arg;
  try {

    rocksdb::port::WindowsThread th(&StartThreadWrapper, state.get());
    state.release();

    std::lock_guard<std::mutex> lg(mu_);
    threads_to_join_.push_back(std::move(th));

  } catch (const std::system_error& ex) {
    WinthreadCall("start thread", ex.code());
  }
}

void WinEnvThreads::WaitForJoin() {
  for (auto& th : threads_to_join_) {
    th.join();
  }
  threads_to_join_.clear();
}

unsigned int WinEnvThreads::GetThreadPoolQueueLen(Env::Priority pri) const {
  assert(pri >= Env::Priority::BOTTOM && pri <= Env::Priority::HIGH);
  return thread_pools_[pri].GetQueueLen();
}

uint64_t WinEnvThreads::gettid() {
  uint64_t thread_id = GetCurrentThreadId();
  return thread_id;
}

uint64_t WinEnvThreads::GetThreadID() const { return gettid(); }

void  WinEnvThreads::SleepForMicroseconds(int micros) {
  std::this_thread::sleep_for(std::chrono::microseconds(micros));
}

void WinEnvThreads::SetBackgroundThreads(int num, Env::Priority pri) {
  assert(pri >= Env::Priority::BOTTOM && pri <= Env::Priority::HIGH);
  thread_pools_[pri].SetBackgroundThreads(num);
}

int WinEnvThreads::GetBackgroundThreads(Env::Priority pri) {
  assert(pri >= Env::Priority::BOTTOM && pri <= Env::Priority::HIGH);
  return thread_pools_[pri].GetBackgroundThreads();
}

void WinEnvThreads::IncBackgroundThreadsIfNeeded(int num, Env::Priority pri) {
  assert(pri >= Env::Priority::BOTTOM && pri <= Env::Priority::HIGH);
  thread_pools_[pri].IncBackgroundThreadsIfNeeded(num);
}

/////////////////////////////////////////////////////////////////////////
// WinEnv

WinEnv::WinEnv() : winenv_io_(this), winenv_threads_(this) {
  // Protected member of the base class
  thread_status_updater_ = CreateThreadStatusUpdater();
}


WinEnv::~WinEnv() {
  // All threads must be joined before the deletion of
  // thread_status_updater_.
  delete thread_status_updater_;
}

Status WinEnv::GetThreadList(
  std::vector<ThreadStatus>* thread_list) {
  assert(thread_status_updater_);
  return thread_status_updater_->GetThreadList(thread_list);
}

Status WinEnv::DeleteFile(const std::string& fname) {
  return winenv_io_.DeleteFile(fname);
}

Status WinEnv::GetCurrentTime(int64_t* unix_time) {
  return winenv_io_.GetCurrentTime(unix_time);
}

Status  WinEnv::NewSequentialFile(const std::string& fname,
  std::unique_ptr<SequentialFile>* result,
  const EnvOptions& options) {
  return winenv_io_.NewSequentialFile(fname, result, options);
}

Status WinEnv::NewRandomAccessFile(const std::string& fname,
  std::unique_ptr<RandomAccessFile>* result,
  const EnvOptions& options) {
  return winenv_io_.NewRandomAccessFile(fname, result, options);
}

Status WinEnv::NewWritableFile(const std::string& fname,
                               std::unique_ptr<WritableFile>* result,
                               const EnvOptions& options) {
  return winenv_io_.OpenWritableFile(fname, result, options, false);
}

Status WinEnv::ReopenWritableFile(const std::string& fname,
    std::unique_ptr<WritableFile>* result, const EnvOptions& options) {
  return winenv_io_.OpenWritableFile(fname, result, options, true);
}

Status WinEnv::NewRandomRWFile(const std::string & fname,
  unique_ptr<RandomRWFile>* result, const EnvOptions & options) {
  return winenv_io_.NewRandomRWFile(fname, result, options);
}

Status WinEnv::NewDirectory(const std::string& name,
  std::unique_ptr<Directory>* result) {
  return winenv_io_.NewDirectory(name, result);
}

Status WinEnv::FileExists(const std::string& fname) {
  return winenv_io_.FileExists(fname);
}

Status WinEnv::GetChildren(const std::string& dir,
  std::vector<std::string>* result) {
  return winenv_io_.GetChildren(dir, result);
}

Status WinEnv::CreateDir(const std::string& name) {
  return winenv_io_.CreateDir(name);
}

Status WinEnv::CreateDirIfMissing(const std::string& name) {
  return winenv_io_.CreateDirIfMissing(name);
}

Status WinEnv::DeleteDir(const std::string& name) {
  return winenv_io_.DeleteDir(name);
}

Status WinEnv::GetFileSize(const std::string& fname,
  uint64_t* size) {
  return winenv_io_.GetFileSize(fname, size);
}

Status  WinEnv::GetFileModificationTime(const std::string& fname,
  uint64_t* file_mtime) {
  return winenv_io_.GetFileModificationTime(fname, file_mtime);
}

Status WinEnv::RenameFile(const std::string& src,
  const std::string& target) {
  return winenv_io_.RenameFile(src, target);
}

Status WinEnv::LinkFile(const std::string& src,
  const std::string& target) {
  return winenv_io_.LinkFile(src, target);
}

Status WinEnv::LockFile(const std::string& lockFname,
  FileLock** lock) {
  return winenv_io_.LockFile(lockFname, lock);
}

Status WinEnv::UnlockFile(FileLock* lock) {
  return winenv_io_.UnlockFile(lock);
}

Status  WinEnv::GetTestDirectory(std::string* result) {
  return winenv_io_.GetTestDirectory(result);
}

Status WinEnv::NewLogger(const std::string& fname,
  std::shared_ptr<Logger>* result) {
  return winenv_io_.NewLogger(fname, result);
}

uint64_t WinEnv::NowMicros() {
  return winenv_io_.NowMicros();
}

uint64_t  WinEnv::NowNanos() {
  return winenv_io_.NowNanos();
}

Status WinEnv::GetHostName(char* name, uint64_t len) {
  return winenv_io_.GetHostName(name, len);
}

Status WinEnv::GetAbsolutePath(const std::string& db_path,
  std::string* output_path) {
  return winenv_io_.GetAbsolutePath(db_path, output_path);
}

std::string WinEnv::TimeToString(uint64_t secondsSince1970) {
  return winenv_io_.TimeToString(secondsSince1970);
}

void  WinEnv::Schedule(void(*function)(void*), void* arg, Env::Priority pri,
  void* tag,
  void(*unschedFunction)(void* arg)) {
  return winenv_threads_.Schedule(function, arg, pri, tag, unschedFunction);
}

int WinEnv::UnSchedule(void* arg, Env::Priority pri) {
  return winenv_threads_.UnSchedule(arg, pri);
}

void WinEnv::StartThread(void(*function)(void* arg), void* arg) {
  return winenv_threads_.StartThread(function, arg);
}

void WinEnv::WaitForJoin() {
  return winenv_threads_.WaitForJoin();
}

unsigned int  WinEnv::GetThreadPoolQueueLen(Env::Priority pri) const {
  return winenv_threads_.GetThreadPoolQueueLen(pri);
}

uint64_t WinEnv::GetThreadID() const {
  return winenv_threads_.GetThreadID();
}

void WinEnv::SleepForMicroseconds(int micros) {
  return winenv_threads_.SleepForMicroseconds(micros);
}

// Allow increasing the number of worker threads.
void  WinEnv::SetBackgroundThreads(int num, Env::Priority pri) {
  return winenv_threads_.SetBackgroundThreads(num, pri);
}

int WinEnv::GetBackgroundThreads(Env::Priority pri) {
  return winenv_threads_.GetBackgroundThreads(pri);
}

void  WinEnv::IncBackgroundThreadsIfNeeded(int num, Env::Priority pri) {
  return winenv_threads_.IncBackgroundThreadsIfNeeded(num, pri);
}

EnvOptions WinEnv::OptimizeForLogWrite(const EnvOptions& env_options,
  const DBOptions& db_options) const {
  return winenv_io_.OptimizeForLogWrite(env_options, db_options);
}

EnvOptions WinEnv::OptimizeForManifestWrite(
  const EnvOptions& env_options) const {
  return winenv_io_.OptimizeForManifestWrite(env_options);
}

}  // namespace port

std::string Env::GenerateUniqueId() {
  std::string result;

  UUID uuid;
  UuidCreateSequential(&uuid);

  RPC_CSTR rpc_str;
  auto status = UuidToStringA(&uuid, &rpc_str);
  (void)status;
  assert(status == RPC_S_OK);

  result = reinterpret_cast<char*>(rpc_str);

  status = RpcStringFreeA(&rpc_str);
  assert(status == RPC_S_OK);

  return result;
}

}  // namespace rocksdb