Notes/UNB/Year 4/Semester 1/CS3418/10-27-2023.md

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2024-01-22 10:12:48 -04:00
Lecture Topic: Producer Consumer & Reader Writer Problem
[Lecture 20](https://lms.unb.ca/d2l/le/content/231539/viewContent/2623161/View)
If you were to use two semaphores and a mutex you can have multiple producers and multiple consumers.
Producer
```c
while(true) {
// produce am item
wait(empty)
wait(mutex)
buffer[index] = item
index++
signal(mutex)
signal(full)
}
```
Consumer
```c
while(true) {
// consume an item
wait(empty)
wait(mutex)
item = buffer[index]
index--
signal(mutex)
signal(full)
}
```
[Slides Chapter 7](https://lms.unb.ca/d2l/le/content/231539/viewContent/2622059/View)
In the reader writer problem, you can encounter the "First reader-writer problem", in which the writer process never writes. A "second reader-writer problem" in which when a writer is ready to write, no reader is available. These problems can sometimes be solved by kernel reader writer locks.
[Dining Philosopher problem](https://en.wikipedia.org/wiki/Dining_philosophers_problem)
[Slides Chapter 8](https://lms.unb.ca/d2l/le/content/231539/viewContent/2623159/View)
Deadlock Characterization:
Deadlocks can occur if four conditions are true simultaneously
- Mutual exclusion: only one process can use a resource