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Author Archives: Niall Cooling
Mutex vs. Semaphores – Part 3 (final part): Mutual Exclusion Problems
As hopefully you can see from the previous posting, the mutex is a significantly safer mechanism to use for implementing mutual exclusion around shared resources. Nevertheless, there are still a couple of problems that use of the mutex (in preference to the semaphore) will not solve. These are:
Circular deadlock
Non-cooperation
Circular Deadlock
Circular deadlock, often referred to as the “deadly embrace” problem is a condition where two or more tasks develop a circular dependency of mutual exclusion. Simply put, one task is blocked […]
Posted in RTOS
Tagged Deadlock, Deadly Embrace, Monitor, Mutex, Priority Ceiling Protocol, RTOS
14 Comments
Mutex vs. Semaphores – Part 2: The Mutex
In Part 1 of this series we looked at the history of the binary and counting semaphore, and then went on to discuss some of the associated problem areas. In this posting I aim to show how a different RTOS construct, the mutex, may overcome some, if not all, of these weaknesses.
To address the problems associated with semaphore, a new concept was developed during the late 1980’s. I have struggled to find it’s first clear definition, but the major use […]
Mutex vs. Semaphores – Part 1: Semaphores
It never ceases to amaze me how often I see postings in newsgroups, etc. asking the difference between a semaphore and a mutex. Probably what baffles me more is that over 90% of the time the responses given are either incorrect or missing the key differences. The most often quoted response is that of the “The Toilet Example (c) Copyright 2005, Niclas Winquist” . This summarises the differences as:
A mutex is really a semaphore with value 1
No, no and no […]
Getting started is always the hardest thing…
I’ve been procrastinating for the best part of a couple of months now getting this blog started. First of all I do feel a little late to the party, has blogging been surpassed by tweeting? Strangely I’ve actually been using twitter in anger since late march (@feabhas) and I’ll cover my experiences of that in a later post.So what is the aim of this blog? My hope is to cover, in a no-nonsense manner, aspects centered on Real-Time and Embedded […]
Posted in General
5 Comments