# Extra Clang Tools 22.1.2 documentation

## clang-tidy - modernize-use-scoped-lock

# modernize-use-scoped-lock

Finds uses of `std::lock_guard` and suggests replacing them with C++17’s alternative `std::scoped_lock`.

Fix-its are provided for single declarations of `std::lock_guard` and warning is emitted for multiple declarations of `std::lock_guard` that can be replaced with a single declaration of `std::scoped_lock`.

## Examples

Single `std::lock_guard` declaration:

    std::mutex M;
    std::lock_guard<std::mutex> L(M);

Transforms to:

    std::mutex M;
    std::scoped_lock L(M);

Single `std::lock_guard` declaration with `std::adopt_lock`:

    std::mutex M;
    std::lock(M);
    std::lock_guard<std::mutex> L(M, std::adopt_lock);

Transforms to:

    std::mutex M;
    std::lock(M);
    std::scoped_lock L(std::adopt_lock, M);

Multiple `std::lock_guard` declarations only emit warnings:

    std::mutex M1, M2;
    std::lock(M1, M2);
    std::lock_guard Lock1(M1, std::adopt_lock); // warning: use single 'std::scoped_lock' instead of multiple 'std::lock_guard'
    std::lock_guard Lock2(M2, std::adopt_lock); // note: additional 'std::lock_guard' declared here

## Limitations

The check will not emit warnings if `std::lock_guard` is used implicitly via `template` parameter:

    template <template <typename> typename Lock>
    void TemplatedLock() {
      std::mutex M;
      Lock<std::mutex> L(M); // no warning
    }

    void instantiate() {
      TemplatedLock<std::lock_guard>();
    }

## Options

WarnOnSingleLocks

  When true, the check will warn on single `std::lock_guard` declarations. Set this option to false if you want to get warnings only on multiple `std::lock_guard` declarations that can be replaced with a single `std::scoped_lock`. Default is true.

WarnOnUsingAndTypedef

  When true, the check will emit warnings if `std::lock_guard` is used in `using` or `typedef` context. Default is true.

      template <typename T>
      using Lock = std::lock_guard<T>; // warning: use 'std::scoped_lock' instead of 'std::lock_guard'

      using LockMutex = std::lock_guard<std::mutex>; // warning: use 'std::scoped_lock' instead of 'std::lock_guard'

      typedef std::lock_guard<std::mutex> LockDef; // warning: use 'std::scoped_lock' instead of 'std::lock_guard'

      using std::lock_guard; // warning: use 'std::scoped_lock' instead of 'std::lock_guard'