Slides: Processes and System Calls

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# Processes and System Calls
## CSC 213 – September  8, 2025

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# Agenda for Today
1. Department Events
2. Upcoming Work
3. Processes & System Calls
4. ~~More C Practice (if there's time)~~
5. Wrap Up

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# Department Events

## CS Table: Developer Experience with AI Coding Assistants
.indent[
  Tuesday, September 9th at noon in JRC 224C  
]

## CS Extra: Off Campus Study in Computer Science
.indent[
  Thursday, September 11th at 4:15pm in Noyce 3821
]

*To receive 0.25% extra credit, 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 1: Ngram Generator

**Due:** Monday, September 8th by 11:59pm

## Questions
**Getting the starter code produces a `git` error. What should I do?**  
The `git` error will print a command you should run first, then you can retry.
Or run this command first and `git` should stop complaining:
```
git config --global --add safe.directory "*"
```

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# Assignment 2: Sorted List

**Due:** Monday, September 15th by 11:59pm

Let's take a quick look at the assignment.

## Questions
*None yet.*

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# Processes & System Calls

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# Discussion: Process Basics
**Questions for think, pair, share:**

1. What is a process, and why is it a useful abstraction for the OS to provide?

2. What is a system call, and why do we need this abstraction?

3. What is limited direct execution?

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

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# Process API: Example 1
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  printf("Hello,\n");
  fork();
  printf("world.\n");
}
```

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# Process API: Example 2
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  int counter = 0;
  fork();
  counter++;
  printf("counter is %d\n", counter);
}
```

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# Process API: Example 3
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  pid_t child_id = fork();
  if (child_id == 0) {
    printf("A\n");
  } else if (child_id > 0) {
    printf("B\n");
  } else {
    perror("fork failed");
    exit(EXIT_FAILURE);
  }
}
```

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# Process API: Example 4
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  pid_t child_id = fork();
  if (child_id == 0) {
    printf("A\n");
  } else if (child_id > 0) {
    wait(NULL);
    printf("B\n");
  } else {
    perror("fork failed");
    exit(EXIT_FAILURE);
  }
}
```

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# Process API: Example 5
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  printf("A\n");
  execlp("ls", "ls", "-l", NULL);
  printf("B\n");
}
```

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# Process API: Example 6
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  printf("A\n");
  execlp("ls", "noyce", "-l", NULL);
  printf("B\n");
}
```

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# Process API: Example 7
What output do you expect this program to produce?
Assume all necessary includes are above the provided code.

```c
int main() {
  printf("A\n");
  execlp("noyce", "ls", "-l", NULL);
  printf("B\n");
}
```

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# Process API: Example 8
What output do you expect this program to produce?

```c
int main() {
  pid_t child_id = fork();
  if (child_id == 0) {
    execlp("ls", "ls", "-l", NULL);
    perror("exec failed");
    exit(EXIT_FAILURE);
  } else if (child_id > 0) {
    int status;
    wait(&status);
    printf("Child exited with status %d\n", WEXITSTATUS(status));
  } else {
    perror("fork failed");
    exit(EXIT_FAILURE);
  }
}
```

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# More C Practice *(if there's time)*

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# More C Practice: Stack Implementation
We are going to implement a stack that stores integers.
Before we start, we should answer two questions:

1. What is the *interface* for a stack of integers?
   That is, what functions will we use to interact with stacks?

2. How will we store the stacks's contents?

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

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# Stack Implementation

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# Wrap Up

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# Reminders

## Assignment
The Ngram Generator assignment is due tonight.
Don't forget to review the C style guidelines from last week's class slides.

The sorted list assignment is due next Monday.
We'll follow this schedule for most of the semester.

## Reading
Review lab instructions before class