update user module to 2021autumn version

user/src/bin/test3_stride2.rs

@@ -0,0 +1,39 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+use user_lib::{get_time, set_priority};
+
+fn spin_delay() {
+    let mut j = true;
+    for _ in 0..10 {
+        j = !j;
+    }
+}
+
+// to get enough accuracy, MAX_TIME (the running time of each process) should > 1000 mseconds.
+const MAX_TIME: isize = 1000;
+fn count_during(prio: isize) -> isize {
+    let start_time = get_time();
+    let mut acc = 0;
+    set_priority(prio);
+    loop {
+        spin_delay();
+        acc += 1;
+        if acc % 400 == 0 {
+            let time = get_time() - start_time;
+            if time > MAX_TIME {
+                return acc;
+            }
+        }
+    }
+}
+
+#[no_mangle]
+pub fn main() -> usize {
+    let prio = 7;
+    let count = count_during(prio);
+    println!("priority = {}, exitcode = {}", prio, count);
+    0
+}