A Real Example of Inversion

The Ingredients:     The Mars Pathfinder spacecraft was run by a uniprocessor that contained an information bus used for passing information between different components of the spacecraft. Access to the bus was synchronised using mutexes. There were (at least) three threads:

1.

a high priority bus management thread that runs frequently for a short time to control the flow of data through the bus.

2.

a long running medium priority communication task for transmitting data back to earth.

3.

a low priority meteorological thread that ran infrequently.

The Outcome:     Shortly after Pathfinder bounced down to mars, and after it began collecting meteorological data, the spacecraft began experiencing total system resets. Frequent complete reboots of the on-board computer.