Monthly Archives: October 2009

Task Synchronisation

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

Synchronisation is an everyday event, both in the real-world and the computer program. For example meeting a friend for a coffee requires synchronisation, in that both parties need to arrive within a given timeframe to make the event worthwhile (sometimes referred to as a rendezvous – however this tends to have more romantic implications). Alternatively, receiving a PO via fax is a form of synchronisation. The company waiting on the PO will-not/cannot start working on the project until this event […]

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Mutex vs. Semaphores – Part 3 (final part): Mutual Exclusion Problems

Niall Cooling

Director at Feabhas Limited
Co-Founder and Director of Feabhas since 1995.
Niall has been designing and programming embedded systems for over 30 years. He has worked in different sectors, including aerospace, telecomms, government and banking.
His current interest lie in IoT Security and Agile for Embedded Systems.

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 […]

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