Advanced Mutual Exclusion
Synchronization primitives can be built like the examples below by using the solutions explained above:
- Locks
- Reentrant mutexes
- Semaphores
- Monitors
- Message passing
- Tuple space
Many forms of mutual exclusion have side-effects. For example, classic semaphores permit deadlocks, in which one process gets a semaphore, another process gets a second semaphore, and then both wait forever for the other semaphore to be released. Other common side-effects include starvation, in which a process never gets sufficient resources to run to completion, priority inversion in which a higher priority thread waits for a lower-priority thread, and "high latency" in which response to interrupts is not prompt.
Much research is aimed at eliminating the above effects, such as by guaranteeing non-blocking progress. No perfect scheme is known.
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