QValueSpacePublisher Class Reference

Detailed Description

The QValueSpacePublisher class allows applications to publish values in the Value Space.

When multiple Value Space layers are available QValueSpacePublisher only publishes values to the layer with the highest order. The layers that QValueSpacePublisher can access can be limited by specifying either a filter or a QUuid at construction time.

The lifetime of values published in the Value Space is specified by the particular Value Space layer that the value is published in. For details on the different behaviors see QValueSpace::LayerOption.

Once a value is published all applications in the system will have read access to it via the QValueSpaceSubscriber class.

Although, logically, the Value Space is a simple collection of hierarchical paths, these paths can conceptually be visualized as a set of objects with attributes. For example, rather than viewing the following list as 12 distinct Value Space paths:

    /Device/Network/Interfaces/eth0/Name
    /Device/Network/Interfaces/eth0/Type
    /Device/Network/Interfaces/eth0/Status
    /Device/Network/Interfaces/eth0/BytesSent
    /Device/Network/Interfaces/eth0/BytesReceived
    /Device/Network/Interfaces/eth0/Time
    /Device/Network/Interfaces/ppp0/Name
    /Device/Network/Interfaces/ppp0/Type
    /Device/Network/Interfaces/ppp0/Status
    /Device/Network/Interfaces/ppp0/BytesSent
    /Device/Network/Interfaces/ppp0/BytesReceived
    /Device/Network/Interfaces/ppp0/Time

it can be thought of as describing two Value Space objects, { /Device/Network/Interfaces/eth0, /Device/Network/Interfaces/ppp0 }, each with the six attributes {Name, Type, Status, BytesSent, BytesReceived, Time}. The QValueSpacePublisher class encapsulates this abstraction.

For performance reasons the setting of and removing of attributes is buffered internally by the QValueSpacePublisher and applied as a batch sometime later. Normally this occurs the next time the application enters the Qt event loop, but this behavior should not be relied upon. If an application must synchronize with others, the QValueSpacePublisher::sync() and QValueSpacePublisher::syncAll() functions can be used to force the application of changes. This call is generally unnecessary, and should be used sparingly to prevent unnecessary load on the system.

See also QValueSpaceSubscriber.

Member Function Documentation

    QValueSpacePublisher publisher("/Device");
    publisher.setValue("State", "Starting");
    publisher.setValue("State/Memory", "1000");
    publisher.sync();
    // QValueSpaceSubscriber("/Device/State").value() == QVariant("Starting")
    // QValueSpaceSubscriber("/Device/State/Memory").value() == QVariant("1000")

    publisher.resetValue("State");
    publisher.sync();
    // QValueSpaceSubscriber("/Device/State").value() == QVariant();
    // QValueSpaceSubscriber("/Device/State/Memory").value() == QVariant();

    QValueSpacePublisher publisher("/Device");
    publisher.setValue("State", "Starting");
    publisher.sync();

    // QValueSpaceSubscriber("/Device/State").value() == QVariant("Starting")