RTI Connext Modern C++ API
Version 5.3.0
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Kinds of communication status. More...
Kinds of communication status.
Each concrete dds::core::Entity is associated with a set of Status objects whose value represents the communication status of that entity. Each status value can be accessed with a corresponding method on the dds::core::Entity.
When these status values change, the corresponding dds::core::cond::StatusCondition objects are activated and the proper Listener objects are invoked to asynchronously inform the application.
An application is notified of communication status by means of the Listener or the dds::core::cond::WaitSet / dds::core::cond::Condition mechanism. The two mechanisms may be combined in the application (e.g., using dds::core::cond::WaitSet (s) / dds::core::cond::Condition (s) to access the data and Listener (s) to be warned asynchronously of erroneous communication statuses).
It is likely that the application will choose one or the other mechanism for each particular communication status (not both). However, if both mechanisms are enabled, then the Listener mechanism is used first and then the dds::core::cond::WaitSet objects are signalled.
The statuses may be classified into:
Read communication statuses are treated slightly differently than the others because they don't change independently. In other words, at least two changes will appear at the same time (dds::core::status::StatusMask::data_on_readers() and dds::core::status::StatusMask::data_available()) and even several of the last kind may be part of the set. This 'grouping' has to be communicated to the application.
For each plain communication status, there is a corresponding structure to hold the status value. These values contain the information related to the change of status, as well as information related to the statuses themselves (e.g., contains cumulative counts).
Associated with each one of an dds::core::Entity's communication status is a logical StatusChangedFlag
. This flag indicates whether that particular communication status has changed since the last time the status was read by the application. The way the status changes is slightly different for the Plain Communication Status and the Read Communication status.
StatusChangedFlag
indicates if status has changedFor the plain communication status, the StatusChangedFlag
flag is initially set to FALSE. It becomes TRUE whenever the plain communication status changes and it is reset to false each time the application accesses the plain communication status via the proper getter operation on the dds::core::Entity.
The communication status is also reset to FALSE whenever the associated listener operation is called as the listener implicitly accesses the status which is passed as a parameter to the operation. The fact that the status is reset prior to calling the listener means that if the application calls the getter from inside the listener it will see the status already reset.
An exception to this rule is when the associated listener is the 'nil' listener. The 'nil' listener is treated as a NOOP and the act of calling the 'nil' listener does not reset the communication status.
For example, the value of the StatusChangedFlag
associated with the dds::core::status::StatusMask::requested_deadline_missed() will become TRUE each time new deadline occurs (which increases dds::core::status::RequestedDeadlineMissedStatus::total_count). The value changes to FALSE when the application accesses the status via the corresponding dds::sub::DataReader::requested_deadline_missed_status method on the proper Entity
StatusChangedFlag
for plain communication statusFor the read communication status, the StatusChangedFlag
flag is initially set to FALSE. The StatusChangedFlag
becomes TRUE when either a data-sample arrives or else the dds::sub::status::ViewState, dds::sub::status::SampleState, or dds::sub::status::InstanceState of any existing sample changes for any reason other than a call to dds::sub::DataReader::read, dds::sub::DataReader::take or their variants. Specifically any of the following events will cause the StatusChangedFlag
to become TRUE:
The arrival of new data.
A change in the dds::sub::status::InstanceState of a contained instance. This can be caused by either:
Depending on the kind of StatusChangedFlag
, the flag transitions to FALSE again as follows:
StatusChangedFlag
becomes FALSE when either the corresponding listener operation (on_data_available) is called or the read or take operation (or their variants) is called on the associated dds::sub::DataReader. StatusChangedFlag
becomes FALSE when any of the following events occurs: StatusChangedFlag
for read communication status