libcamera: object: Add an asynchronous method invocation method

Add a helper invokeMethod() to the Object class that allows asynchrnous
invocation of any method of an Object instance. Asynchronous invocation
occurs when control returns to the event dispatcher of the target
object's thread, in the context of that thread.

To support this, generalise the SignalMessage implementation to support
automatic deletion of the associated BoundMethod, and rename the message
to InvokeMessage to reflect the more generic purpose.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/message.cpp

@@ -7,6 +7,8 @@
 
 #include "message.h"
 
+#include <libcamera/signal.h>
+
 #include "log.h"
 
 /**
@@ -43,8 +45,8 @@ std::atomic_uint Message::nextUserType_{ Message::UserMessage };
  * \brief The message type
  * \var Message::None
  * \brief Invalid message type
- * \var Message::SignalMessage
- * \brief Asynchronous signal delivery across threads
+ * \var Message::InvokeMessage
+ * \brief Asynchronous method invocation across threads
  * \var Message::UserMessage
  * \brief First value available for user-defined messages
  */
@@ -107,25 +109,47 @@ Message::Type Message::registerMessageType()
 }
 
 /**
- * \class SignalMessage
- * \brief A message carrying a Signal across threads
+ * \class InvokeMessage
+ * \brief A message carrying a method invocation across threads
  */
 
 /**
- * \fn SignalMessage::SignalMessage()
- * \brief Construct a SignalMessage
- * \param[in] method The slot that the signal targets
- * \param[in] pack The signal arguments
+ * \brief Construct an InvokeMessage for method invocation on an Object
+ * \param[in] method The bound method
+ * \param[in] pack The packed method arguments
+ * \param[in] deleteMethod True to delete the \a method when the message is
+ * destroyed
+ */
+InvokeMessage::InvokeMessage(BoundMethodBase *method, void *pack,
+			     bool deleteMethod)
+	: Message(Message::InvokeMessage), method_(method), pack_(pack),
+	  deleteMethod_(deleteMethod)
+{
+}
+
+InvokeMessage::~InvokeMessage()
+{
+	if (deleteMethod_)
+		delete method_;
+}
+
+/**
+ * \brief Invoke the method bound to InvokeMessage::method_ with arguments
+ * InvokeMessage::pack_
+ */
+void InvokeMessage::invoke()
+{
+	method_->invokePack(pack_);
+}
+
+/**
+ * \var InvokeMessage::method_
+ * \brief The method to be invoked
  */
 
 /**
- * \var SignalMessage::method_
- * \brief The slot that the signal targets
- */
-
-/**
- * \var SignalMessage::pack_
- * \brief The signal arguments
+ * \var InvokeMessage::pack_
+ * \brief The packed method invocation arguments
  */
 
 }; /* namespace libcamera */