4 files changed, 53 insertions, 0 deletions
diff --git a/include/libcamera/internal/message.h b/include/libcamera/internal/message.h
index 92ea64a5..f1b133bf 100644
--- a/include/libcamera/internal/message.h
+++ b/include/libcamera/internal/message.h
@@ -25,6 +25,7 @@ public:
 		None = 0,
 		InvokeMessage = 1,
 		ThreadMoveMessage = 2,
+		DeferredDelete = 3,
 		UserMessage = 1000,
 	};
 
diff --git a/include/libcamera/object.h b/include/libcamera/object.h
index 9a3dd070..a1882f05 100644
--- a/include/libcamera/object.h
+++ b/include/libcamera/object.h
@@ -27,6 +27,8 @@ public:
 	Object(Object *parent = nullptr);
 	virtual ~Object();
 
+	void deleteLater();
+
 	void postMessage(std::unique_ptr<Message> msg);
 
 	template<typename T, typename R, typename... FuncArgs, typename... Args,
diff --git a/src/libcamera/message.cpp b/src/libcamera/message.cpp
index e9b3e73f..bc985c07 100644
--- a/src/libcamera/message.cpp
+++ b/src/libcamera/message.cpp
@@ -49,6 +49,8 @@ std::atomic_uint Message::nextUserType_{ Message::UserMessage };
  * \brief Asynchronous method invocation across threads
  * \var Message::ThreadMoveMessage
  * \brief Object is being moved to a different thread
+ * \var Message::DeferredDelete
+ * \brief Object is scheduled for deletion
  * \var Message::UserMessage
  * \brief First value available for user-defined messages
  */
diff --git a/src/libcamera/object.cpp b/src/libcamera/object.cpp
index 1544a23e..647ccda7 100644
--- a/src/libcamera/object.cpp
+++ b/src/libcamera/object.cpp
@@ -73,6 +73,10 @@ Object::Object(Object *parent)
  * Deleting an Object automatically disconnects all signals from the Object's
  * slots. All the Object's children are made orphan, but stay bound to their
  * current thread.
+ *
+ * Object instances shall be destroyed from the thread they are bound to,
+ * otherwise undefined behaviour may occur. If deletion of an Object needs to
+ * be scheduled from a different thread, deleteLater() shall be used.
  */
 Object::~Object()
 {
@@ -99,6 +103,46 @@ Object::~Object()
 }
 
 /**
+ * \brief Schedule deletion of the instance in the thread it belongs to
+ *
+ * This function schedules deletion of the Object when control returns to the
+ * event loop that the object belongs to. This ensures the object is destroyed
+ * from the right context, as required by the libcamera threading model.
+ *
+ * If this function is called before the thread's event loop is started, the
+ * object will be deleted when the event loop starts.
+ *
+ * Deferred deletion can be used to control the destruction context with shared
+ * pointers. An object managed with shared pointers is deleted when the last
+ * reference is destroyed, which makes difficult to ensure through software
+ * design which context the deletion will take place in. With a custom deleter
+ * for the shared pointer using deleteLater(), the deletion can be guaranteed to
+ * happen in the thread the object is bound to.
+ *
+ * \code{.cpp}
+ * std::shared_ptr<MyObject> createObject()
+ * {
+ *     struct Deleter : std::default_delete<MyObject> {
+ *             void operator()(MyObject *obj)
+ *             {
+ *                     delete obj;
+ *             }
+ *     };
+ *
+ *     MyObject *obj = new MyObject();
+ *
+ *     return std::shared_ptr<MyObject>(obj, Deleter());
+ * }
+ * \endcode
+ *
+ * \context This function is \threadsafe.
+ */
+void Object::deleteLater()
+{
+	postMessage(std::make_unique<Message>(Message::DeferredDelete));
+}
+
+/**
  * \brief Post a message to the object's thread
  * \param[in] msg The message
  *
@@ -144,6 +188,10 @@ void Object::message(Message *msg)
 		break;
 	}
 
+	case Message::DeferredDelete:
+		delete this;
+		break;
+
 	default:
 		break;
 	}