Real Time Model

Transformational Model

According to which a program begins and ends, turning data into results or output data.

Reactive Model

According to which a program may execute indefinitely a sequence of instructions, for example operating on a data stream.

Real Time Model

Reactive model in which the program has to keep synchronized with the input data stream, which thus imposes time constraints to the program.

Processes, threads, tasks, activities and jobs

Definition of task (process, thread, activity)

Sequence of activations (instances or jobs), each consisting of a set of instructions that, in the absence of other activities, is performed by the CPU without interruption.

Deadline types

Deadline is the most common temporal requirement.

• D - Relative deadline. Time measured from activation.

• di - Absolute deadline. Absolute time instant, regarding the ith activation, in which the task must finish.

  • di = ri + D

There are other types of task requirements: window, synchronization, distance, ...

Task Temporal Characterization

Example of task temporal characterization (there are other forms).

Periodic

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• Examples:

Sporadic

• Similar to periodic, but miti replaces Ti and Φi usually is not used (tough it could be used to specify a minimum delay until the first activation).

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• Examples: