Clean up env_posix.cc.

General cleanup principles: * Use override when applicable. * Remove static when redundant (methods and globals in anonymous namespaces). * Use const on class members where possible. * Standardize on "status" for Status local variables. * Renames where clarity can be improved. * Qualify standard library names with std:: when possible, to distinguish from POSIX names. * Qualify POSIX names with the global namespace (::) when possible, to distinguish from standard library names. This also refactors the background thread synchronization logic so that it's statically analyzable. ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=219212089
6 年之前 · 1cb3840881
--- a/util/env_posix.cc
+++ b/util/env_posix.cc
@ -3,22 +3,21 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.

 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>

 #include <atomic>
 #include <cerrno>
 #include <cstddef>
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <limits>
 #include <queue>
@ -26,6 +25,7 @@
 #include <string>
 #include <thread>
 #include <type_traits>
 #include <utility>

 #include "leveldb/env.h"
 #include "leveldb/slice.h"
@ -45,16 +45,22 @@ namespace leveldb {

 namespace {

 static int open_read_only_file_limit = -1;
 static int mmap_limit = -1;
 // Set by EnvPosixTestHelper::SetReadOnlyMMapLimit() and MaxOpenFiles().
 int g_open_read_only_file_limit = -1;

 // Up to 1000 mmap regions for 64-bit binaries; none for 32-bit.
 constexpr const int kDefaultMmapLimit = (sizeof(void*) >= 8) ? 1000 : 0;

 // Can be set using EnvPosixTestHelper::SetReadOnlyMMapLimit.
 int g_mmap_limit = kDefaultMmapLimit;

 constexpr const size_t kWritableFileBufferSize = 65536;

 static Status PosixError(const std::string& context, int err_number) {
  if (err_number == ENOENT) {
    return Status::NotFound(context, strerror(err_number));
 Status PosixError(const std::string& context, int error_number) {
  if (error_number == ENOENT) {
    return Status::NotFound(context, std::strerror(error_number));
  } else {
    return Status::IOError(context, strerror(err_number));
    return Status::IOError(context, std::strerror(error_number));
  }
 }

@ -97,124 +103,147 @@ class Limiter {
  std::atomic<int> acquires_allowed_;
 };

 class PosixSequentialFile: public SequentialFile {
 private:
  std::string filename_;
  int fd_;

 // Implements sequential read access in a file using read().
 //
 // Instances of this class are thread-friendly but not thread-safe, as required
 // by the SequentialFile API.
 class PosixSequentialFile final : public SequentialFile {
 public:
  PosixSequentialFile(const std::string& fname, int fd)
      : filename_(fname), fd_(fd) {}
  virtual ~PosixSequentialFile() { close(fd_); }
  PosixSequentialFile(std::string filename, int fd)
      : fd_(fd), filename_(filename) {}
  ~PosixSequentialFile() override { close(fd_); }

  virtual Status Read(size_t n, Slice* result, char* scratch) {
    Status s;
  Status Read(size_t n, Slice* result, char* scratch) override {
    Status status;
    while (true) {
      ssize_t r = read(fd_, scratch, n);
      if (r < 0) {
      ::ssize_t read_size = ::read(fd_, scratch, n);
      if (read_size < 0) {  // Read error.
        if (errno == EINTR) {
          continue;  // Retry
        }
        s = PosixError(filename_, errno);
        status = PosixError(filename_, errno);
        break;
      }
      *result = Slice(scratch, r);
      *result = Slice(scratch, read_size);
      break;
    }
    return s;
    return status;
  }

  virtual Status Skip(uint64_t n) {
    if (lseek(fd_, n, SEEK_CUR) == static_cast<off_t>(-1)) {
  Status Skip(uint64_t n) override {
    if (::lseek(fd_, n, SEEK_CUR) == static_cast<off_t>(-1)) {
      return PosixError(filename_, errno);
    }
    return Status::OK();
  }
 };

 // pread() based random-access
 class PosixRandomAccessFile: public RandomAccessFile {
 private:
  std::string filename_;
  bool temporary_fd_;  // If true, fd_ is -1 and we open on every read.
  int fd_;
  Limiter* limiter_;
  const int fd_;
  const std::string filename_;
 };

 // Implements random read access in a file using pread().
 //
 // Instances of this class are thread-safe, as required by the RandomAccessFile
 // API. Instances are immutable and Read() only calls thread-safe library
 // functions.
 class PosixRandomAccessFile final : public RandomAccessFile {
 public:
  PosixRandomAccessFile(const std::string& fname, int fd, Limiter* limiter)
      : filename_(fname), fd_(fd), limiter_(limiter) {
    temporary_fd_ = !limiter->Acquire();
    if (temporary_fd_) {
      // Open file on every access.
      close(fd_);
      fd_ = -1;
  // The new instance takes ownership of |fd|. |fd_limiter| must outlive this
  // instance, and will be used to determine if .
  PosixRandomAccessFile(std::string filename, int fd, Limiter* fd_limiter)
      : has_permanent_fd_(fd_limiter->Acquire()),
        fd_(has_permanent_fd_ ? fd : -1),
        fd_limiter_(fd_limiter),
        filename_(std::move(filename)) {
    if (!has_permanent_fd_) {
      assert(fd_ == -1);
      ::close(fd);  // The file will be opened on every read.
    }
  }

  virtual ~PosixRandomAccessFile() {
    if (!temporary_fd_) {
      close(fd_);
      limiter_->Release();
  ~PosixRandomAccessFile() override {
    if (has_permanent_fd_) {
      assert(fd_ != -1);
      ::close(fd_);
      fd_limiter_->Release();
    }
  }

  virtual Status Read(uint64_t offset, size_t n, Slice* result,
                      char* scratch) const {
  Status Read(uint64_t offset, size_t n, Slice* result,
              char* scratch) const override {
    int fd = fd_;
    if (temporary_fd_) {
      fd = open(filename_.c_str(), O_RDONLY);
    if (!has_permanent_fd_) {
      fd = ::open(filename_.c_str(), O_RDONLY);
      if (fd < 0) {
        return PosixError(filename_, errno);
      }
    }

    Status s;
    ssize_t r = pread(fd, scratch, n, static_cast<off_t>(offset));
    *result = Slice(scratch, (r < 0) ? 0 : r);
    if (r < 0) {
      // An error: return a non-ok status
      s = PosixError(filename_, errno);
    assert(fd != -1);

    Status status;
    ssize_t read_size = ::pread(fd, scratch, n, static_cast<off_t>(offset));
    *result = Slice(scratch, (read_size < 0) ? 0 : read_size);
    if (read_size < 0) {
      // An error: return a non-ok status.
      status = PosixError(filename_, errno);
    }
    if (temporary_fd_) {
    if (!has_permanent_fd_) {
      // Close the temporary file descriptor opened earlier.
      close(fd);
      assert(fd != fd_);
      ::close(fd);
    }
    return s;
    return status;
  }
 };

 // mmap() based random-access
 class PosixMmapReadableFile: public RandomAccessFile {
 private:
  std::string filename_;
  void* mmapped_region_;
  size_t length_;
  Limiter* limiter_;
  const bool has_permanent_fd_;  // If false, the file is opened on every read.
  const int fd_;  // -1 if has_permanent_fd_ is false.
  Limiter* const fd_limiter_;
  const std::string filename_;
 };

 // Implements random read access in a file using mmap().
 //
 // Instances of this class are thread-safe, as required by the RandomAccessFile
 // API. Instances are immutable and Read() only calls thread-safe library
 // functions.
 class PosixMmapReadableFile final : public RandomAccessFile {
 public:
  // base[0,length-1] contains the mmapped contents of the file.
  PosixMmapReadableFile(const std::string& fname, void* base, size_t length,
                        Limiter* limiter)
      : filename_(fname), mmapped_region_(base), length_(length),
        limiter_(limiter) {
  }
  // mmap_base[0, length-1] points to the memory-mapped contents of the file. It
  // must be the result of a successful call to mmap(). This instances takes
  // over the ownership of the region.
  //
  // |mmap_limiter| must outlive this instance. The caller must have already
  // aquired the right to use one mmap region, which will be released when this
  // instance is destroyed.
  PosixMmapReadableFile(std::string filename, char* mmap_base, size_t length,
                        Limiter* mmap_limiter)
      : mmap_base_(mmap_base), length_(length), mmap_limiter_(mmap_limiter),
        filename_(std::move(filename)) {}

  virtual ~PosixMmapReadableFile() {
    munmap(mmapped_region_, length_);
    limiter_->Release();
  ~PosixMmapReadableFile() override {
    ::munmap(static_cast<void*>(mmap_base_), length_);
    mmap_limiter_->Release();
  }

  virtual Status Read(uint64_t offset, size_t n, Slice* result,
                      char* scratch) const {
    Status s;
  Status Read(uint64_t offset, size_t n, Slice* result,
              char* scratch) const override {
    if (offset + n > length_) {
      *result = Slice();
      s = PosixError(filename_, EINVAL);
    } else {
      *result = Slice(reinterpret_cast<char*>(mmapped_region_) + offset, n);
      return PosixError(filename_, EINVAL);
    }
    return s;

    *result = Slice(mmap_base_ + offset, n);
    return Status::OK();
  }

 private:
  char* const mmap_base_;
  const size_t length_;
  Limiter* const mmap_limiter_;
  const std::string filename_;
 };

 class PosixWritableFile final : public WritableFile {
@ -378,30 +407,39 @@ class PosixWritableFile final : public WritableFile {
  const std::string dirname_;  // The directory of filename_.
 };

 static int LockOrUnlock(int fd, bool lock) {
 int LockOrUnlock(int fd, bool lock) {
  errno = 0;
  struct flock f;
  memset(&f, 0, sizeof(f));
  f.l_type = (lock ? F_WRLCK : F_UNLCK);
  f.l_whence = SEEK_SET;
  f.l_start = 0;
  f.l_len = 0;        // Lock/unlock entire file
  return 
fcntl(fd, F_SETLK, &f);
  struct ::flock file_lock_info;
  std::memset(&file_lock_info, 0, sizeof(file_lock_info));
  file_lock_info.l_type = (lock ? F_WRLCK : F_UNLCK);
  file_lock_info.l_whence = SEEK_SET;
  file_lock_info.l_start = 0;
  file_lock_info.l_len = 0;  // Lock/unlock entire file.
  return ::fcntl(fd, F_SETLK, &file_lock_info);
 }

 // Instances are thread-safe because they are immutable.
 class PosixFileLock : public FileLock {
 public:
  int fd_;
  std::string name_;
  PosixFileLock(int fd, std::string filename)
      : fd_(fd), filename_(std::move(filename)) {}

  int fd() const { return fd_; }
  const std::string& filename() const { return filename_; }

 private:
  const int fd_;
  const std::string filename_;
 };

 // Set of locked files.  We keep a separate set instead of just
 // relying on fcntrl(F_SETLK) since fcntl(F_SETLK) does not provide
 // any protection against multiple uses from the same process.
 // Tracks the files locked by PosixEnv::LockFile().
 //
 // We maintain a separate set instead of relying on fcntrl(F_SETLK) because
 // fcntl(F_SETLK) does not provide any protection against multiple uses from the
 // same process.
 //
 // Instances are thread-safe because all member data is guarded by a mutex.
 class PosixLockTable {
 private:
  port::Mutex mu_;
  std::set<std::string> locked_files_ GUARDED_BY(mu_);
 public:
  bool Insert(const std::string& fname) LOCKS_EXCLUDED(mu_) {
    mu_.Lock();
@ -414,217 +452,225 @@ class PosixLockTable {
    locked_files_.erase(fname);
    mu_.Unlock();
  }

 private:
  port::Mutex mu_;
  std::set<std::string> locked_files_ GUARDED_BY(mu_);
 };

 class PosixEnv : public Env {
 public:
  PosixEnv();
  virtual ~PosixEnv() {
    char msg[] = "Destroying Env::Default()\n";
    fwrite(msg, 1, sizeof(msg), stderr);
    abort();
  ~PosixEnv() override {
    static char msg[] = "PosixEnv singleton destroyed. Unsupported behavior!\n";
    std::fwrite(msg, 1, sizeof(msg), stderr);
    std::abort();
  }

  virtual Status NewSequentialFile(const std::string& fname,
                                   SequentialFile** result) {
    int fd = open(fname.c_str(), O_RDONLY);
  Status NewSequentialFile(const std::string& filename,
                           SequentialFile** result) override {
    int fd = ::open(filename.c_str(), O_RDONLY);
    if (fd < 0) {
      *result = nullptr;
      return PosixError(fname, errno);
    } else {
      *result = new PosixSequentialFile(fname, fd);
      return Status::OK();
      return PosixError(filename, errno);
    }

    *result = new PosixSequentialFile(filename, fd);
    return Status::OK();
  }

  virtual Status NewRandomAccessFile(const std::string& fname,
                                     RandomAccessFile** result) {
  Status NewRandomAccessFile(const std::string& filename,
                             RandomAccessFile** result) override {
    *result = nullptr;
    Status s;
    int fd = open(fname.c_str(), O_RDONLY);
    int fd = ::open(filename.c_str(), O_RDONLY);
    if (fd < 0) {
      s = PosixError(fname, errno);
    } else if (mmap_limit_.Acquire()) {
      uint64_t size;
      s = GetFileSize(fname, &size);
      if (s.ok()) {
        void* base = mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0);
        if (base != MAP_FAILED) {
          *result = new PosixMmapReadableFile(fname, base, size, &mmap_limit_);
        } else {
          s = PosixError(fname, errno);
        }
      }
      close(fd);
      if (!s.ok()) {
        mmap_limit_.Release();
      return PosixError(filename, errno);
    }

    if (!mmap_limiter_.Acquire()) {
      *result = new PosixRandomAccessFile(filename, fd, &fd_limiter_);
      return Status::OK();
    }

    uint64_t file_size;
    Status status = GetFileSize(filename, &file_size);
    if (status.ok()) {
      void* mmap_base = ::mmap(/*addr=*/nullptr, file_size, PROT_READ,
                               MAP_SHARED, fd, 0);
      if (mmap_base != MAP_FAILED) {
        *result = new PosixMmapReadableFile(
            filename, reinterpret_cast<char*>(mmap_base), file_size,
            &mmap_limiter_);
      } else {
        status = PosixError(filename, errno);
      }
    } else {
      *result = new PosixRandomAccessFile(fname, fd, &fd_limit_);
    }
    return s;
    ::close(fd);
    if (!status.ok()) {
      mmap_limiter_.Release();
    }
    return status;
  }

  virtual Status NewWritableFile(const std::string& fname,
                                 WritableFile** result) {
    Status s;
    int fd = open(fname.c_str(), O_TRUNC | O_WRONLY | O_CREAT, 0644);
  Status NewWritableFile(const std::string& filename,
                         WritableFile** result) override {
    int fd = ::open(filename.c_str(), O_TRUNC | O_WRONLY | O_CREAT, 0644);
    if (fd < 0) {
      *result = nullptr;
      s = PosixError(fname, errno);
    } else {
      *result = new PosixWritableFile(fname, fd);
      return PosixError(filename, errno);
    }
    return s;

    *result = new PosixWritableFile(filename, fd);
    return Status::OK();
  }

  virtual Status NewAppendableFile(const std::string& fname,
                                   WritableFile** result) {
    Status s;
    int fd = open(fname.c_str(), O_APPEND | O_WRONLY | O_CREAT, 0644);
  Status NewAppendableFile(const std::string& filename,
                           WritableFile** result) override {
    int fd = ::open(filename.c_str(), O_APPEND | O_WRONLY | O_CREAT, 0644);
    if (fd < 0) {
      *result = nullptr;
      s = PosixError(fname, errno);
    } else {
      *result = new PosixWritableFile(fname, fd);
      return PosixError(filename, errno);
    }
    return s;

    *result = new PosixWritableFile(filename, fd);
    return Status::OK();
  }

  virtual bool FileExists(const std::string& fname) {
    return 
access(fname.c_str(), F_OK) == 0;
  bool FileExists(const std::string& filename) override {
    return ::access(filename.c_str(), F_OK) == 0;
  }

  virtual Status GetChildren(const std::string& dir,
                             std::vector<std::string>* result) {
  Status GetChildren(const std::string& directory_path,
                     std::vector<std::string>* result) override {
    result->clear();
    DIR* d = opendir(dir.c_str());
    if (d == nullptr) {
      return PosixError(dir, errno);
    ::DIR* dir = ::opendir(directory_path.c_str());
    if (dir == nullptr) {
      return PosixError(directory_path, errno);
    }
    struct dirent* entry;
    while ((entry = readdir(d)) != nullptr) {
      result->push_back(entry->d_name);
    struct ::dirent* entry;
    while ((entry = ::readdir(dir)) != nullptr) {
      result->emplace_back(entry->d_name);
    }
    closedir(d);
    ::closedir(dir);
    return Status::OK();
  }

  virtual Status DeleteFile(const std::string& fname) {
    Status result;
    if (unlink(fname.c_str()) != 0) {
      result = PosixError(fname, errno);
  Status DeleteFile(const std::string& filename) override {
    if (::unlink(filename.c_str()) != 0) {
      return PosixError(filename, errno);
    }
    return result;
    return Status::OK();
  }

  virtual Status CreateDir(const std::string& name) {
    Status result;
    if (mkdir(name.c_str(), 0755) != 0) {
      result = PosixError(name, errno);
  Status CreateDir(const std::string& dirname) override {
    if (::mkdir(dirname.c_str(), 0755) != 0) {
      return PosixError(dirname, errno);
    }
    return result;
    return Status::OK();
  }

  virtual Status DeleteDir(const std::string& name) {
    Status result;
    if (rmdir(name.c_str()) != 0) {
      result = PosixError(name, errno);
  Status DeleteDir(const std::string& dirname) override {
    if (::rmdir(dirname.c_str()) != 0) {
      return PosixError(dirname, errno);
    }
    return result;
    return Status::OK();
  }

  virtual Status GetFileSize(const std::string& fname, uint64_t* size) {
    Status s;
    struct stat sbuf;
    if (stat(fname.c_str(), &sbuf) != 0) {
  Status GetFileSize(const std::string& filename, uint64_t* size) override {
    struct ::stat file_stat;
    if (::stat(filename.c_str(), &file_stat) != 0) {
      *size = 0;
      s = PosixError(fname, errno);
    } else {
      *size = sbuf.st_size;
      return PosixError(filename, errno);
    }
    return s;
    *size = file_stat.st_size;
    return Status::OK();
  }

  virtual Status RenameFile(const std::string& src, const std::string& target) {
    Status result;
    if (rename(src.c_str(), target.c_str()) != 0) {
      result = PosixError(src, errno);
  Status RenameFile(const std::string& from, const std::string& to) override {
    if (std::rename(from.c_str(), to.c_str()) != 0) {
      return PosixError(from, errno);
    }
    return result;
    return Status::OK();
  }

  virtual Status LockFile(const std::string& fname, FileLock** lock) {
  Status LockFile(const std::string& filename, FileLock** lock) override {
    *lock = nullptr;
    Status result;
    int fd = open(fname.c_str(), O_RDWR | O_CREAT, 0644);

    int fd = ::open(filename.c_str(), O_RDWR | O_CREAT, 0644);
    if (fd < 0) {
      result = PosixError(fname, errno);
    } else if (!locks_.Insert(fname)) {
      close(fd);
      result = Status::IOError("lock " + fname, "already held by process");
    } else if (LockOrUnlock(fd, true) == -1) {
      result = PosixError("lock " + fname, errno);
      close(fd);
      locks_.Remove(fname);
    } else {
      PosixFileLock* my_lock = new PosixFileLock;
      my_lock->fd_ = fd;
      my_lock->name_ = fname;
      *lock = my_lock;
      return PosixError(filename, errno);
    }

    if (!locks_.Insert(filename)) {
      ::close(fd);
      return Status::IOError("lock " + filename, "already held by process");
    }

    if (LockOrUnlock(fd, true) == -1) {
      int lock_errno = errno;
      ::close(fd);
      locks_.Remove(filename);
      return PosixError("lock " + filename, lock_errno);
    }
    return result;

    *lock = new PosixFileLock(fd, filename);
    return Status::OK();
  }

  virtual Status UnlockFile(FileLock* lock) {
    PosixFileLock* my_lock = reinterpret_cast<PosixFileLock*>(lock);
    Status result;
    if (LockOrUnlock(my_lock->fd_, false) == -1) {
      result = PosixError("unlock", errno);
  Status UnlockFile(FileLock* lock) override {
    PosixFileLock* posix_file_lock = static_cast<PosixFileLock*>(lock);
    if (LockOrUnlock(posix_file_lock->fd(), false) == -1) {
      return PosixError("unlock " + posix_file_lock->filename(), errno);
    }
    locks_.Remove(my_lock->name_);
    close(my_lock->fd_);
    delete my_lock;
    return result;
    locks_.Remove(posix_file_lock->filename());
    ::close(posix_file_lock->fd());
    delete posix_file_lock;
    return Status::OK();
  }

  virtual void Schedule(void (*function)(void*), void* arg);
  void Schedule(void (*background_work_function)(void* background_work_arg),
                void* background_work_arg) override;

  virtual void StartThread(void (*function)(void* arg), void* arg);
  void StartThread(void (*thread_main)(void* thread_main_arg),
                   void* thread_main_arg) override;

  virtual Status GetTestDirectory(std::string* result) {
    const char* env = getenv("TEST_TMPDIR");
  Status GetTestDirectory(std::string* result) override {
    const char* env = std::getenv("TEST_TMPDIR");
    if (env && env[0] != '\0') {
      *result = env;
    } else {
      char buf[100];
      snprintf(buf, sizeof(buf), "/tmp/leveldbtest-%d", int(geteuid()));
      std::snprintf(buf, sizeof(buf), "/tmp/leveldbtest-%d",
                    static_cast<int>(::geteuid()));
      *result = buf;
    }
    // Directory may already exist

    // The CreateDir status is ignored because the directory may already exist.
    CreateDir(*result);

    return Status::OK();
  }

  virtual Status NewLogger(const std::string& fname, Logger** result) {
    FILE* f = fopen(fname.c_str(), "w");
    if (f == nullptr) {
  Status NewLogger(const std::string& filename, Logger** result) override {
    std::FILE* fp = std::fopen(filename.c_str(), "w");
    if (fp == nullptr) {
      *result = nullptr;
      return PosixError(fname, errno);
      return PosixError(filename, errno);
    } else {
      *result = new PosixLogger(f);
      *result = new PosixLogger(fp);
      return Status::OK();
    }
  }

  virtual uint64_t NowMicros() {
    struct timeval tv;
    gettimeofday(&tv, nullptr);
    return static_cast<uint64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
  uint64_t NowMicros() override {
    static constexpr uint64_t kUsecondsPerSecond = 1000000;
    struct ::timeval tv;
    ::gettimeofday(&tv, nullptr);
    return static_cast<uint64_t>(tv.tv_sec) * kUsecondsPerSecond + tv.tv_usec;
  }

  virtual void SleepForMicroseconds(int micros) {
    usleep(micros);
  void SleepForMicroseconds(int micros) override {
    ::usleep(micros);
  }

 private:
@ -656,44 +702,41 @@ class PosixEnv : public Env {
  std::queue<BackgroundWorkItem> background_work_queue_
      GUARDED_BY(background_work_mutex_);

  PosixLockTable locks_;
  Limiter mmap_limit_;
  Limiter fd_limit_;
  PosixLockTable locks_;  // Thread-safe.
  Limiter mmap_limiter_;  // Thread-safe.
  Limiter fd_limiter_;  // Thread-safe.
 };

 // Return the maximum number of concurrent mmaps.
 static int MaxMmaps() {
  if (mmap_limit >= 0) {
    return mmap_limit;
  }
  // Up to 1000 mmaps for 64-bit binaries; none for smaller pointer sizes.
  mmap_limit = sizeof(void*) >= 8 ? 1000 : 0;
  return mmap_limit;
 int MaxMmaps() {
  return g_mmap_limit;
 }

 // Return the maximum number of read-only files to keep open.
 static intptr_t MaxOpenFiles() {
  if (open_read_only_file_limit >= 0) {
    return open_read_only_file_limit;
 int MaxOpenFiles() {
  if (g_open_read_only_file_limit >= 0) {
    return g_open_read_only_file_limit;
  }
  struct rlimit rlim;
  if (getrlimit(RLIMIT_NOFILE, &rlim)) {
  struct ::rlimit rlim;
  if (::getrlimit(RLIMIT_NOFILE, &rlim)) {
    // getrlimit failed, fallback to hard-coded default.
    open_read_only_file_limit = 50;
    g_open_read_only_file_limit = 50;
  } else if (rlim.rlim_cur == RLIM_INFINITY) {
    open_read_only_file_limit = std::numeric_limits<int>::max();
    g_open_read_only_file_limit = std::numeric_limits<int>::max();
  } else {
    // Allow use of 20% of available file descriptors for read-only files.
    open_read_only_file_limit = rlim.rlim_cur / 5;
    g_open_read_only_file_limit = rlim.rlim_cur / 5;
  }
  return open_read_only_file_limit;
  return g_open_read_only_file_limit;
 }

 }  // namespace

 PosixEnv::PosixEnv()
    : background_work_cv_(&background_work_mutex_),
      started_background_thread_(false),
      mmap_limit_(MaxMmaps()),
      fd_limit_(MaxOpenFiles()) {
      mmap_limiter_(MaxMmaps()),
      fd_limiter_(MaxOpenFiles()) {
 }

 void PosixEnv::Schedule(
@ -737,6 +780,8 @@ void PosixEnv::BackgroundThreadMain() {
  }
 }

 namespace {

 // Wraps an Env instance whose destructor is never created.
 //
 // Intended usage:
@ -800,12 +845,12 @@ void PosixEnv::StartThread(void (*thread_main)(void* thread_main_arg),

 void EnvPosixTestHelper::SetReadOnlyFDLimit(int limit) {
  PosixDefaultEnv::AssertEnvNotInitialized();
  open_read_only_file_limit = limit;
  g_open_read_only_file_limit = limit;
 }

 void EnvPosixTestHelper::SetReadOnlyMMapLimit(int limit) {
  PosixDefaultEnv::AssertEnvNotInitialized();
  mmap_limit = limit;
  g_mmap_limit = limit;
 }

 Env* Env::Default() {