Merge recent update from ch7 && cargo clippy

user/src/bin/sync_sem.rs

@@ -9,7 +9,7 @@ extern crate alloc;
 use user_lib::{semaphore_create, semaphore_up, semaphore_down};
 use user_lib::{thread_create, waittid, sleep};
 use user_lib::exit;
-use alloc::vec::Vec;
+use alloc::vec;
 
 const SEM_SYNC: usize = 0;
 
@@ -33,9 +33,10 @@ pub fn main() -> i32 {
     // create semaphores
     assert_eq!(semaphore_create(0) as usize, SEM_SYNC);
     // create threads
-    let mut threads = Vec::new();
-    threads.push(thread_create(first as usize, 0));
-    threads.push(thread_create(second as usize, 0));
+    let threads = vec![
+        thread_create(first as usize, 0),
+        thread_create(second as usize, 0),
+    ];
     // wait for all threads to complete
     for thread in threads.iter() {
         waittid(*thread as usize);