[libcamera-devel] [PATCH v6 3/6] ipa: raspberrypi: Switch to std::scoped_lock in the Metadata class

[David Plowman]

HI Naush

Thanks for this patch. I must confess I haven't encountered this
"scoped_lock" before, but it seems to be just the ticket.

On Mon, 10 May 2021 at 10:59, Naushir Patuck <naush at raspberrypi.com> wrote:
>
> Replace std::lock_guard with std::scoped_lock. When locking a single
> mutex, both are functionally the same. When locking two mutexes in the
> operator= overload, the scoped_lock uses a deadlock avoidance algorithm
> to avoid deadlock.
>
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>

Reviewed-by: David Plowman <david.plowman at raspberrypi.com>

Thanks!
David

> ---
>  src/ipa/raspberrypi/controller/metadata.hpp | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/src/ipa/raspberrypi/controller/metadata.hpp b/src/ipa/raspberrypi/controller/metadata.hpp
> index 07dd28ed9e0a..e735cfbe0480 100644
> --- a/src/ipa/raspberrypi/controller/metadata.hpp
> +++ b/src/ipa/raspberrypi/controller/metadata.hpp
> @@ -22,14 +22,14 @@ public:
>         template<typename T>
>         void Set(std::string const &tag, T const &value)
>         {
> -               std::lock_guard<std::mutex> lock(mutex_);
> +               std::scoped_lock lock(mutex_);
>                 data_[tag] = value;
>         }
>
>         template<typename T>
>         int Get(std::string const &tag, T &value) const
>         {
> -               std::lock_guard<std::mutex> lock(mutex_);
> +               std::scoped_lock lock(mutex_);
>                 auto it = data_.find(tag);
>                 if (it == data_.end())
>                         return -1;
> @@ -39,14 +39,13 @@ public:
>
>         void Clear()
>         {
> -               std::lock_guard<std::mutex> lock(mutex_);
> +               std::scoped_lock lock(mutex_);
>                 data_.clear();
>         }
>
>         Metadata &operator=(Metadata const &other)
>         {
> -               std::lock_guard<std::mutex> lock(mutex_);
> -               std::lock_guard<std::mutex> other_lock(other.mutex_);
> +               std::scoped_lock lock(mutex_, other.mutex_);
>                 data_ = other.data_;
>                 return *this;
>         }
> --
> 2.25.1
>
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