Post-class 02/24

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@@ -118,3 +118,7 @@ int fibonacci(int n){
 	return ans;
 }
 ```
+
+---
+
+[-> Notes 02/21](02-21.md)
diff --git a/02-21.md b/02-21.md
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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