====== F.7 Deadline ======
[[dido:public:ra:xapend:xapend.f_qos:start| Return to DDS Quality of Service ]]

  
The [[dido:public:ra:xapend:xapend.a_glossary:d:deadline_qos|DEADLINE]] [[dido:public:ra:xapend:xapend.a_glossary:p:policy|Policy]] is useful for cases where a [[dido:public:ra:xapend:xapend.a_glossary:t:topic|Topic]] is expected to have each [[dido:public:ra:xapend:xapend.a_glossary:i:instance|instance]] updated periodically. On the publishing side this setting establishes a contract that the [[dido:public:ra:xapend:xapend.a_glossary:a:application|application]] must meet. On the subscribing side the setting establishes a minimum [[dido:public:ra:xapend:xapend.a_glossary:r:requirement|requirement]] for the remote publishers that are expected to supply the data values.

When the Service ‘matches’ a ''DataWriter'' and a ''DataReader'' it checks whether the settings are compatible (i.e., offered deadline period<= requested deadline period) if they are not, the two entities are informed (via the [[dido:public:ra:xapend:xapend.a_glossary:l:listener|listener]] or [[dido:public:ra:xapend:xapend.a_glossary:c:condition|condition]] mechanism) of the incompatibility of the [[dido:public:ra:xapend:xapend.a_glossary:q:qos|QoS]] settings and communication will not occur.

Assuming that the reader and writer ends have compatible settings, the fulfillment of this contract is monitored by the Service and the application is informed of any violations by means of the proper listener or condition.
The value offered is considered compatible with the value requested if and only if the inequality “offered deadline ''period <= '' requested deadline ''period''” evaluates to ''TRUE''.

The setting of the DEADLINE policy must be set consistently with that of the TIME_BASED_FILTER. For these two policies to be consistent the settings must be such that ''deadline period>= minimum_separation''".

Source: [[https://www.omg.org/spec/DDS/1.4/PDF | DDS 1.4 Spec]]

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