[v2,3/5] libcamera: controls: Implement move ctor/assignment
diff mbox series

Message ID 20250421153556.171192-4-barnabas.pocze@ideasonboard.com
State New
Headers show
Series
  • libcamera: controls: Move constructor/assignment + swap
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Commit Message

Barnabás Pőcze April 21, 2025, 3:35 p.m. UTC 
Implement a move constructor and move assignment operator for `ControlValue`.
The `ControlValue` type already has an "empty" state that is used when
creating a default constructed `ControlValue`, so have the moved-from
instance return to that state after move construction/assignment.

This is useful, for example, for `std::vector` as most implementations will
use the copy constructor when reallocating if no nothrow move constructor
is available. Having a nothrow move constructor avoids the extra copies.
It is also useful when using temporaries of `ControlValue` with other
containers such as `std::optional`, and it also makes `ControlInfo`
"cheaply" move constructible/assignable.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
---
 include/libcamera/controls.h | 26 ++++++++++++++++++++++++++
 src/libcamera/controls.cpp   | 18 ++++++++++++++++++
 2 files changed, 44 insertions(+)

Comments

Jacopo Mondi Nov. 21, 2025, 11:47 a.m. UTC | #1 
Hi Barnabás

On Mon, Apr 21, 2025 at 05:35:54PM +0200, Barnabás Pőcze wrote:
> Implement a move constructor and move assignment operator for `ControlValue`.
> The `ControlValue` type already has an "empty" state that is used when
> creating a default constructed `ControlValue`, so have the moved-from
> instance return to that state after move construction/assignment.
>
> This is useful, for example, for `std::vector` as most implementations will
> use the copy constructor when reallocating if no nothrow move constructor
> is available. Having a nothrow move constructor avoids the extra copies.
> It is also useful when using temporaries of `ControlValue` with other
> containers such as `std::optional`, and it also makes `ControlInfo`
> "cheaply" move constructible/assignable.
>
> Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> ---
>  include/libcamera/controls.h | 26 ++++++++++++++++++++++++++
>  src/libcamera/controls.cpp   | 18 ++++++++++++++++++
>  2 files changed, 44 insertions(+)
>
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index 3f3580036..866d667c4 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -14,6 +14,7 @@
>  #include <stdint.h>
>  #include <string>
>  #include <unordered_map>
> +#include <utility>
>  #include <vector>
>
>  #include <libcamera/base/class.h>
> @@ -165,6 +166,31 @@ public:
>  	ControlValue(const ControlValue &other);
>  	ControlValue &operator=(const ControlValue &other);
>
> +	ControlValue(ControlValue &&other) noexcept
> +		: type_(other.type_),

Is it necessary to reset the other's type to ControlTypeNone ?

> +		  isArray_(std::exchange(other.isArray_, false)),
> +		  numElements_(std::exchange(other.numElements_, 0)),
> +		  storage_(std::exchange(other.storage_, {}))
> +	{
> +		other.type_ = ControlTypeNone;
> +	}
> +
> +	ControlValue &operator=(ControlValue &&other) noexcept
> +	{
> +		if (this != &other) {
> +			release();
> +
> +			type_ = other.type_;
> +			isArray_ = std::exchange(other.isArray_, false);
> +			numElements_ = std::exchange(other.numElements_, 0);
> +			storage_ = std::exchange(other.storage_, {});
> +
> +			other.type_ = ControlTypeNone;
> +		}
> +
> +		return *this;
> +	}
> +
>  	ControlType type() const { return type_; }
>  	bool isNone() const { return type_ == ControlTypeNone; }
>  	bool isArray() const { return isArray_; }
> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
> index d384e1ef7..135e87613 100644
> --- a/src/libcamera/controls.cpp
> +++ b/src/libcamera/controls.cpp
> @@ -155,6 +155,24 @@ ControlValue &ControlValue::operator=(const ControlValue &other)
>  	return *this;
>  }
>
> +/**
> + * \fn ControlValue::ControlValue(ControlValue &&other) noexcept
> + * \brief Move constructor for ControlValue
> + * \param[in] other The ControlValue object to move from
> + *
> + * Move constructs a ControlValue instance from \a other.
> + * After this operation \a other will be in the same state
> + * as a default constructed ControlValue instance.
> + */
> +
> +/**
> + * \fn ControlValue &ControlValue::operator=(ControlValue &&other) noexcept
> + * \brief Move assignment operator for ControlValue
> + * \param[in] other The ControlValue object to move from
> + *
> + * \sa ControlValue::ControlValue(ControlValue &&other)
> + */
> +
>  /**
>   * \fn ControlValue::type()
>   * \brief Retrieve the data type of the value
> --
> 2.49.0
>
Barnabás Pőcze Nov. 21, 2025, 12:49 p.m. UTC | #2 
2025. 11. 21. 12:47 keltezéssel, Jacopo Mondi írta:
> Hi Barnabás
> 
> On Mon, Apr 21, 2025 at 05:35:54PM +0200, Barnabás Pőcze wrote:
>> Implement a move constructor and move assignment operator for `ControlValue`.
>> The `ControlValue` type already has an "empty" state that is used when
>> creating a default constructed `ControlValue`, so have the moved-from
>> instance return to that state after move construction/assignment.
>>
>> This is useful, for example, for `std::vector` as most implementations will
>> use the copy constructor when reallocating if no nothrow move constructor
>> is available. Having a nothrow move constructor avoids the extra copies.
>> It is also useful when using temporaries of `ControlValue` with other
>> containers such as `std::optional`, and it also makes `ControlInfo`
>> "cheaply" move constructible/assignable.
>>
>> Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
>> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
>> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
>> ---
>>   include/libcamera/controls.h | 26 ++++++++++++++++++++++++++
>>   src/libcamera/controls.cpp   | 18 ++++++++++++++++++
>>   2 files changed, 44 insertions(+)
>>
>> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
>> index 3f3580036..866d667c4 100644
>> --- a/include/libcamera/controls.h
>> +++ b/include/libcamera/controls.h
>> @@ -14,6 +14,7 @@
>>   #include <stdint.h>
>>   #include <string>
>>   #include <unordered_map>
>> +#include <utility>
>>   #include <vector>
>>
>>   #include <libcamera/base/class.h>
>> @@ -165,6 +166,31 @@ public:
>>   	ControlValue(const ControlValue &other);
>>   	ControlValue &operator=(const ControlValue &other);
>>
>> +	ControlValue(ControlValue &&other) noexcept
>> +		: type_(other.type_),
> 
> Is it necessary to reset the other's type to ControlTypeNone ?

I think so. Since the underlying storage is moved, the previous type cannot always
be kept because there would no longer be storage (e.g. if it is a bigger array).
So setting it to none unconditionally seems the best decision to me.


> 
>> +		  isArray_(std::exchange(other.isArray_, false)),
>> +		  numElements_(std::exchange(other.numElements_, 0)),
>> +		  storage_(std::exchange(other.storage_, {}))
>> +	{
>> +		other.type_ = ControlTypeNone;
>> +	}
>> +
>> +	ControlValue &operator=(ControlValue &&other) noexcept
>> +	{
>> +		if (this != &other) {
>> +			release();
>> +
>> +			type_ = other.type_;
>> +			isArray_ = std::exchange(other.isArray_, false);
>> +			numElements_ = std::exchange(other.numElements_, 0);
>> +			storage_ = std::exchange(other.storage_, {});
>> +
>> +			other.type_ = ControlTypeNone;
>> +		}
>> +
>> +		return *this;
>> +	}
>> +
>>   	ControlType type() const { return type_; }
>>   	bool isNone() const { return type_ == ControlTypeNone; }
>>   	bool isArray() const { return isArray_; }
>> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
>> index d384e1ef7..135e87613 100644
>> --- a/src/libcamera/controls.cpp
>> +++ b/src/libcamera/controls.cpp
>> @@ -155,6 +155,24 @@ ControlValue &ControlValue::operator=(const ControlValue &other)
>>   	return *this;
>>   }
>>
>> +/**
>> + * \fn ControlValue::ControlValue(ControlValue &&other) noexcept
>> + * \brief Move constructor for ControlValue
>> + * \param[in] other The ControlValue object to move from
>> + *
>> + * Move constructs a ControlValue instance from \a other.
>> + * After this operation \a other will be in the same state
>> + * as a default constructed ControlValue instance.
>> + */
>> +
>> +/**
>> + * \fn ControlValue &ControlValue::operator=(ControlValue &&other) noexcept
>> + * \brief Move assignment operator for ControlValue
>> + * \param[in] other The ControlValue object to move from
>> + *
>> + * \sa ControlValue::ControlValue(ControlValue &&other)
>> + */
>> +
>>   /**
>>    * \fn ControlValue::type()
>>    * \brief Retrieve the data type of the value
>> --
>> 2.49.0
>>

Patch
diff mbox series 

diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
index 3f3580036..866d667c4 100644
--- a/include/libcamera/controls.h
+++ b/include/libcamera/controls.h
@@ -14,6 +14,7 @@ 
 #include <stdint.h>
 #include <string>
 #include <unordered_map>
+#include <utility>
 #include <vector>
 
 #include <libcamera/base/class.h>
@@ -165,6 +166,31 @@  public:
 	ControlValue(const ControlValue &other);
 	ControlValue &operator=(const ControlValue &other);
 
+	ControlValue(ControlValue &&other) noexcept
+		: type_(other.type_),
+		  isArray_(std::exchange(other.isArray_, false)),
+		  numElements_(std::exchange(other.numElements_, 0)),
+		  storage_(std::exchange(other.storage_, {}))
+	{
+		other.type_ = ControlTypeNone;
+	}
+
+	ControlValue &operator=(ControlValue &&other) noexcept
+	{
+		if (this != &other) {
+			release();
+
+			type_ = other.type_;
+			isArray_ = std::exchange(other.isArray_, false);
+			numElements_ = std::exchange(other.numElements_, 0);
+			storage_ = std::exchange(other.storage_, {});
+
+			other.type_ = ControlTypeNone;
+		}
+
+		return *this;
+	}
+
 	ControlType type() const { return type_; }
 	bool isNone() const { return type_ == ControlTypeNone; }
 	bool isArray() const { return isArray_; }
diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
index d384e1ef7..135e87613 100644
--- a/src/libcamera/controls.cpp
+++ b/src/libcamera/controls.cpp
@@ -155,6 +155,24 @@  ControlValue &ControlValue::operator=(const ControlValue &other)
 	return *this;
 }
 
+/**
+ * \fn ControlValue::ControlValue(ControlValue &&other) noexcept
+ * \brief Move constructor for ControlValue
+ * \param[in] other The ControlValue object to move from
+ *
+ * Move constructs a ControlValue instance from \a other.
+ * After this operation \a other will be in the same state
+ * as a default constructed ControlValue instance.
+ */
+
+/**
+ * \fn ControlValue &ControlValue::operator=(ControlValue &&other) noexcept
+ * \brief Move assignment operator for ControlValue
+ * \param[in] other The ControlValue object to move from
+ *
+ * \sa ControlValue::ControlValue(ControlValue &&other)
+ */
+
 /**
  * \fn ControlValue::type()
  * \brief Retrieve the data type of the value