ALMemory

NAOqi Core - Overview | API | Tutorial

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What it does

ALMemory is a centralized memory used to store all key information related to the hardware configuration of your robot.

More specifically, ALMemory provides information about the current state of the Actuators and the Sensors. For further details, see: Actuator & Sensor list or Actuator & Sensor list.

Customized usage

ALMemory can also be used to store and retrieve named values, and act as a hub for the distribution of event notifications.

How it works

ALMemory is a mutexed and unordered boost map. The map contains variant (ALValue).

Mutex are read/write mutex and for performance, can protect:

• The map
• A value
• The value history (only for events)

For example:

• Remove a data blocks all readers/writers.
• Insert an existing data only blocks the modified data.
• Read data blocks only writers of read data.

The notifications are managed by a threadpool (in local) or by a unique notification thread (in remote).

Event and MicroEvent

An Event is a MicroEvent which stores his history into ALMemory. They are basically the same, but MicroEvent is faster.

You can access to event history using ALMemoryProxy::getEventHistory.

Furthermore a Module can autostart when someone subscribe to an Event. This feature is accessible using ALMemoryProxy::declareEvent with two parameters.

Performances and Limitations

ALMemory is thread safe for normal operations. Reader and writer can access variable at the same moment except when you use ALMemoryProxy::getDataPtr.

ALMemory can store and retrieve variant (ALValue):

type	C++	Python	Java
integer	int	Python integer	int
boolean	bool	Python boolean	Boolean
float	float	Python float	Float
List	vector<ALValue>	[]	Java array []
String	std::string	Python string	String
Binary	ALValue	String	byte[]
Variant	ALValue	Use python type	jnaoqi Variant

Warning

ALMemory only stores 4-byte integers and 4-byte floats. This is not a problem for C++ as it uses the same representation, but Python integers and floats are 8 bytes (or more for big ints). This may lead to a loss of precision when storing values.

Getting started

To access to a value stored in ALMemory, use:

The function ...	Providing ...
ALMemoryProxy::getDataPtr	Fast pointer access. Warning: it’s not thread safe nor atomic.
ALMemoryProxy::getData	Thread safe access. It can be used either when your module is local or remote.

Customized usage

To store values in the memory, use ALMemoryProxy::insertData.

To subscribe to events, use:

The function ...	To subscribe to ...
ALMemoryProxy::subscribeToEvent	an event.
ALMemoryProxy::subscribeToMicroEvent	a microEvent.

For further details, see the following example: Creating events (DEPRECATED).

To generate events, use the following functions:

The function ...	To ...
ALMemoryProxy::raiseMicroEvent	insert a value and notify subscribers.
ALMemoryProxy::raiseEvent	insert a value, notify subscribers, store value history and timestamp (internal).
ALMemoryProxy::declareEvent	link a module to a variable. If a module subscribes to variable, the module starts his process once. For example, subscribe to FaceDetected automatically starts the module ALFaceDetection. If all subscribers unsubscribe, the module stops.