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Fixed a memory safety bug in FastWordpieceTokenizer concerning StringVocab lifetime. This prevents temporary copies that were previously invalidating std::string_view references to internal vocabulary data, ensuring memory stability during tokenization. #1481

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Merged
copybara-service merged 1 commit into from
Feb 25, 2026
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Fixed a memory safety bug in FastWordpieceTokenizer concerning StringVocab lifetime. This prevents temporary copies that were previously invalidating std::string_view references to internal vocabulary data, ensuring memory stability during tokenization. #1481

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6 changes: 3 additions & 3 deletions tensorflow_text/core/kernels/fast_wordpiece_tokenizer_model_builder.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,7 @@ class FastWordpieceBuilder {
trie_array_[node_id] &= 0xFFFFFEFF;
}

absl::optional<StringVocab> vocab_;
std::unique_ptr<StringVocab> vocab_;

int max_bytes_per_token_ = -1;

Expand Down Expand Up @@ -264,7 +264,7 @@ absl::Status FastWordpieceBuilder::BuildModel(
no_pretokenization_ = no_pretokenization;
support_detokenization_ = support_detokenization;

vocab_.emplace(vocab);
vocab_ = std::make_unique<StringVocab>(vocab);
if (vocab_->Size() != vocab.size()) {
return absl::FailedPreconditionError(
"Tokens in the vocabulary must be unique.");
Expand Down Expand Up @@ -830,7 +830,7 @@ absl::Status FastWordpieceBuilder::PrecomputeResultForSuffixIndicator() {
LookupStatus status = WordpieceTokenize(
suffix_indicator_, max_bytes_per_token_, /*max_chars_per_subtoken=*/-1,
suffix_indicator_, /*use_unknown_token=*/true, unk_token_,
/*split_unknown_characters=*/false, &vocab_.value(), &subwords,
/*split_unknown_characters=*/false, vocab_.get(), &subwords,
&begin_offset, &end_offset, &num_word_pieces);
precomputed_result_for_suffix_indicator_.reserve(subwords.size());
if (!status.success) {
Expand Down
4 changes: 2 additions & 2 deletions tensorflow_text/core/kernels/phrase_tokenizer_model_builder.cc
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Expand Up @@ -45,7 +45,7 @@ class PhraseBuilder {
absl::StatusOr<std::string> ExportToFlatBuffer() const;

private:
absl::optional<StringVocab> vocab_;
std::unique_ptr<StringVocab> vocab_;
std::vector<uint32_t> trie_data_;
std::string unk_token_;
int unk_token_id_;
Expand All @@ -64,7 +64,7 @@ absl::Status PhraseBuilder::BuildModel(const std::vector<std::string>& vocab,
prob_ = prob;
split_end_punctuation_ = split_end_punctuation;

vocab_.emplace(vocab);
vocab_ = std::make_unique<StringVocab>(vocab);
if (vocab_->Size() != vocab.size()) {
return absl::FailedPreconditionError(
"Tokens in the vocabulary must be unique.");
Expand Down
1 change: 1 addition & 0 deletions tensorflow_text/core/kernels/string_vocab.cc
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Expand Up @@ -19,6 +19,7 @@ namespace text {

StringVocab::StringVocab(const std::vector<std::string>& vocab)
: vocab_(vocab) {
index_map_.reserve(vocab.size());
for (int i = 0; i < vocab.size(); ++i) {
index_map_[vocab_[i]] = i;
}
Expand Down
2 changes: 2 additions & 0 deletions tensorflow_text/core/kernels/string_vocab.h
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Expand Up @@ -30,6 +30,8 @@ namespace text {
class StringVocab : public WordpieceVocab {
public:
explicit StringVocab(const std::vector<std::string>& vocab);
StringVocab(const StringVocab&) = delete;
StringVocab& operator=(const StringVocab&) = delete;
LookupStatus Contains(absl::string_view key, bool* value) const override;
absl::optional<int> LookupId(absl::string_view key) const;
// Returns the key of `vocab_id` or empty if `vocab_id` is not valid.
Expand Down