Function LockFile

src/leveldb/include/leveldb/env.h:360–362

    return target_->RenameFile(s, t);
  }
  Status LockFile(const std::string& f, FileLock** l) override {
    return target_->LockFile(f, l);
  }
  Status UnlockFile(FileLock* l) override { return target_->UnlockFile(l); }
  void Schedule(void (*f)(void*), void* a) override {
    return target_->Schedule(f, a);