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10. Deadlock

This is an awkward situation where processes have effectively locked themselves out because they are all waiting on each other to do something.

Example:

In this case the scheduler has to deal with the problem.

It can do so by applying an extra rule with regards to resources. For example,

• It does not allow a process to start until all the resources it needs are available
• The scheduler could always allocate resources in the same order
• If a deadlock is detected i.e. processes have been sitting in the WAIT queue for a long time, then the operating system removes a process

All these approaches would work, but once again, each one has its good and bad points.