C++ Expected::keep方法代码示例

Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
                   bool WriteSymtab, object::Archive::Kind Kind,
                   bool Deterministic, bool Thin,
                   std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
  assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");

  SmallString<0> SymNamesBuf;
  raw_svector_ostream SymNames(SymNamesBuf);
  SmallString<0> StringTableBuf;
  raw_svector_ostream StringTable(StringTableBuf);

  Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
      StringTable, SymNames, Kind, Thin, Deterministic, NewMembers);
  if (Error E = DataOrErr.takeError())
    return E;
  std::vector<MemberData> &Data = *DataOrErr;

  if (!StringTableBuf.empty())
    Data.insert(Data.begin(), computeStringTable(StringTableBuf));

  // We would like to detect if we need to switch to a 64-bit symbol table.
  if (WriteSymtab) {
    uint64_t MaxOffset = 0;
    uint64_t LastOffset = MaxOffset;
    for (const auto &M : Data) {
      // Record the start of the member's offset
      LastOffset = MaxOffset;
      // Account for the size of each part associated with the member.
      MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
      // We assume 32-bit symbols to see if 32-bit symbols are possible or not.
      MaxOffset += M.Symbols.size() * 4;
    }

    // The SYM64 format is used when an archive's member offsets are larger than
    // 32-bits can hold. The need for this shift in format is detected by
    // writeArchive. To test this we need to generate a file with a member that
    // has an offset larger than 32-bits but this demands a very slow test. To
    // speed the test up we use this environment variable to pretend like the
    // cutoff happens before 32-bits and instead happens at some much smaller
    // value.
    const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
    int Sym64Threshold = 32;
    if (Sym64Env)
      StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);

    // If LastOffset isn't going to fit in a 32-bit varible we need to switch
    // to 64-bit. Note that the file can be larger than 4GB as long as the last
    // member starts before the 4GB offset.
    if (LastOffset >= (1ULL << Sym64Threshold)) {
      if (Kind == object::Archive::K_DARWIN)
        Kind = object::Archive::K_DARWIN64;
      else
        Kind = object::Archive::K_GNU64;
    }
  }

  Expected<sys::fs::TempFile> Temp =
      sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
  if (!Temp)
    return Temp.takeError();

  raw_fd_ostream Out(Temp->FD, false);
  if (Thin)
    Out << "!<thin>\n";
  else
    Out << "!<arch>\n";

  if (WriteSymtab)
    writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);

  for (const MemberData &M : Data)
    Out << M.Header << M.Data << M.Padding;

  Out.flush();

  // At this point, we no longer need whatever backing memory
  // was used to generate the NewMembers. On Windows, this buffer
  // could be a mapped view of the file we want to replace (if
  // we're updating an existing archive, say). In that case, the
  // rename would still succeed, but it would leave behind a
  // temporary file (actually the original file renamed) because
  // a file cannot be deleted while there's a handle open on it,
  // only renamed. So by freeing this buffer, this ensures that
  // the last open handle on the destination file, if any, is
  // closed before we attempt to rename.
  OldArchiveBuf.reset();

  return Temp->keep(ArcName);
}