Priority ceiling protocol
- Priority ceiling protocol
In real-time computing, the priority ceiling protocol is a synchronization protocol for shared resources to avoid unbounded priority inversion and mutual deadlock due to wrong nesting of critical sections. In this protocol each resource is assigned a priority ceiling, which is a priority equal to the highest priority of any task which may lock the resource.[cite journal]
author = Lui Sha, Ragunathan Rajkumar, and John P. Lehoczky
month = September
year = 1990
title = Priority Inheritance Protocols: An Approach to Real-Time Synchronization
journal = IEEE Transactions on Computers
volume = 39
issue = 9
pages = 1175–1185
issn = 0018-9340
url = http://www-md.e-technik.uni-rostock.de/ma/gol/rtsys-bib/90-toc-pcp.pdf
doi = 10.1109/12.57058] In the Immediate Ceiling Priority Protocol (ICPP) when a task locks the resource its priority is temporarily raised to the priority ceiling of the resource, thus no task that may lock the resource is able to get scheduled. This allows a low priority task to defer execution of higher-priority tasks.
The Original Ceiling Priority Protocol (OCPP) has the same worst-case performance but is subtly different in the implementation which can provide finer grained priority inheritance control mechanism than ICPP.
A task will not get scheduled if any resource it may lock actually has been locked by another task, and therefore the priority ceiling protocol prevents deadlocks.
ICPP is called "Priority Protect Protocol" in POSIX and "Priority Ceiling Emulation" in abbrlink|RTSJ|Real-time specification for Java.[cite book]
title = Real-Time Systems and Programming Languages — Ada 95, Real-Time Java and Real-Time POSIX
month = March
year = 2001
author = Alan Burns, and Andy Wellings
edition = 3rd
publisher = Addison Wesley Longmain
isbn = 0201729881] References
External links
* [http://www.embedded.com/showArticle.jhtml?articleID=20600062 How to use priority inheritance] , by Kyle Renwick and Bill Renwick (2004-05-18)
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