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[\<- Notes 02/14](02-14.md)
---
# Recursion Continued
- Recursion
- Tiny Code
- No Loops
- Condition to Stop (otherwise it will go forever)
- For more, see page 353-355 in textbook
---
# Multi-Threading
## Process
- A process, in the simplest terms, is an executing program
- A process can contain multiple threads
## Threads
- Threads are lightweight processes
- Each process can execute several threads
- The threads execute **independently**
- Threads **share** the global variables and OS resources
- Each thread has its **own stack** and follow its **own execution flow**
- In practice
- Main program creates threads
- By specifying an entry point function and an argument
- The main program and each created thread run independently
- They share global variables
- They do not share local variables
- Example of functions to handle threads
- Creation
- Exit
- Cancellation
- Synchronization
- Example:
- Alternating Threads
- Creates 3 threads
- Let the system execute them in a round-robin fashion
- Wait for them to finish at main
```
int main(){
int i;
for(i = 0; i < 3; i++){
//create thread to execute function loop() with parameter i
}
//wait for each thread to finish
}
void loop(int n){
int i;
for(i = 0; i < 20; i++){
printf("Thread %d\n", n);
sleep(1);
}
}
```
- Need synchronization
- Solution:
- Lock
- Conditional Variables
- Semaphores
---
[-> Notes 02/26](02-26.md)
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