add OnceCell and OnceLock

Author: smallnest

.DS_Store

@@ -12,6 +12,8 @@ fn main() {
     rwlock_example();
 
     once_example();
+    oncecell_example();
+    oncelock_example();
 
     barrier_example();
 

sync_primitive/src/main.rs

@@ -2,7 +2,10 @@
 #![allow(unused_assignments)]
 
 use std::sync::Once;
-
+use std::sync::OnceLock;
+use std::cell::OnceCell;
+use std::thread::sleep;
+use std::time::Duration;
 
 pub fn once_example() {
 	let once = Once::new();
@@ -16,4 +19,38 @@ pub fn once_example() {
 		println!("Once: {}", val);
 	}
 
+}
+
+pub fn oncecell_example() {
+	let cell = OnceCell::new();
+	assert!(cell.get().is_none());
+
+	let value: &String = cell.get_or_init(|| {
+		"Hello, World!".to_string()
+	});
+	assert_eq!(value, "Hello, World!");
+	assert!(cell.get().is_some());
+
+	println!("OnceCell: {}", cell.get().is_some())
+}
+
+pub fn oncelock_example() {
+	static CELL: OnceLock<String> = OnceLock::new();
+	assert!(CELL.get().is_none());
+
+	std::thread::spawn(|| {
+		let value: &String = CELL.get_or_init(|| {
+			"Hello, World!".to_string()
+		});
+		assert_eq!(value, "Hello, World!");
+	}).join().unwrap();
+
+
+	sleep(Duration::from_secs(1));
+
+	let value: Option<&String> = CELL.get();
+	assert!(value.is_some());
+	assert_eq!(value.unwrap().as_str(), "Hello, World!");
+
+	println!("OnceLock: {}", value.is_some())
 }