Slides: Processes and System Calls

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# Processes and System Calls
## CSC 213 – September  4, 2026

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

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# Upcoming Work

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# Assignment 1: Ngram Generator

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

## Questions
**Is remote access to MathLAN working?**  
It seems like it is back now.
This assignment should also work on your own computer if you have a C programming environment set up (regular macOS or Windows with WSL).

**What's the difference between `argv` input and `getchar` input?**
The `argv` array holds command line arguments passed to the program at startup.
When you call `getchar` or similar functions, that's asking the user to type something at that moment after the program has already started.

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# Assignment 2: *Coming Soon*

**Due:** Monday, September 14th by 11:59pm

I will normally release assignments on Mondays, but I'll send this one out later today via email so you can get started if you have time over the long weekend.

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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' 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 on Tuesday night.
I have bookable office hours early next week if you need help.
Don't forget you can also refer to the in-class demos;
the `charsort` example program might include some helpful pieces you could incorporate in your assignment (remember to cite).

Do your best to follow the C code style guidelines from our previous slides.

## Reading
Review the instructions for our first lab before Wednesday's class.
I'll publish these soon.