Synchronous sessions and fixed priority scheduling

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Fixed priority scheduling is usually applied to tasks that communicate only asynchronously. Synchronous communication, although more suitable for some application requirements, is more difficult to analyse, as a task can be blocked several times and the duration of each block is dependent on the behaviour of other tasks. The easy decomposition of temporal behaviour, enabled by the asynchronous model, is lost. This paper defines a means of incorporating synchronous behaviour (via an abstraction called a session) into the computational model of fixed priority scheduling, Ceiling priorities are assigned to sessions, and appropriate scheduling analysis is derived. Example task sets are examined and an implementation in Ada 95 is given. Sessions are abstract constructs and can be used to represent rendezvous, atomic actions, conversations, CA-Actions etc.

Original languageEnglish
Pages (from-to)107-118
Number of pages12
JournalJournal of systems architecture
Issue number2
Publication statusPublished - Nov 1997


  • real-time
  • scheduling
  • fault tolerance

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