Slides: Locks and Locked Data Structures

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# Locks and Locked Data Structures
## CSC 213 – October 12, 2026

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# Agenda for Today
1. Department Events
1. Upcoming Work
1. Locks Discussion
1. Exercise
1. Wrap Up

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# Department Events

## CS Table: Applying CS Methods to Other Fields
.indent[
   Tuesday, October 13th at noon in the CS Commons
]

*To receive a token, send an email to let me know you attended no more than 48 hours after the event.*

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# Upcoming Work

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# Assignment: Filesystem Integrity
**Due:** Monday, October 12th by 11:59pm  
**Late Deadline:** Wednesday, October 14th by 10:00am

## Questions
**Are we assuming something like `fsck` is running when we describe the recovery process?**  
Sort of. 
Explain how a tool like `fsck` could restore the filesystem to a consistent state.
Your explanation doesn't have to match exactly what `fsck` would do.

You can also ignore the task of detecting the exact error that has occured;
you only need to describe the recovery process, not the checking to detect an inconsistent state.

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# Lab: Worm
**Due:** Wednesday, October 14th by 11:59pm  
**Late Deadline:** Monday, October 26th by 11:59pm

## Questions
_No new questions since last class._

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# Locks

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# Discussion: Locks
**Questions for think, pair, share:**

The following questions refer to the two thread functions below, which run concurrently.

```c
int x = 0;
int y = 0;
```
.left-col[
```c
void* thr1(void* arg) {
   if (x == 0) y = 1;
   return NULL;
}
```
]

.right-col[
```c
void* thr2(void* arg) {
   if (y == 0) x = 1;
   return NULL;
}
```
]

1. What values of `x` and `y` are possible after both threads have finished?

2. An execution of a parallel program is *"serializable"* if its output could have resulted from running the threads sequentially instead of concurrently.
   Does the program above always run in a serializable fashion?

*Start by thinking of answers on your own. I will let you know when to start discussion.*

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# Locks Exercise

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# Wrap Up

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# Reminders

## Upcoming Deadlines
- **Filesystem Integrity Assignment:** due tonight, or Wednesday morning with a token
- **Worm Lab:** due Wednesday, or Monday after break with a token

## Need help? Use your resources!
- Book an appointment during office hours
- Attend mentor office hours
- Review slides, readings, and other course resources
- Use tools like `gdb` and AddressSanitizer to catch and diagnose issues

## Reading

- **Condition Variables** (OSTEP, Chapter 30)
            
- **Semaphores** (OSTEP, Chapter 31)