feat: alarm系统调用实现 (#710)

* alarm系统调用实现

user/apps/test_alarm/src/main.rs

@@ -0,0 +1,42 @@
+extern crate libc;
+use libc::{signal, sleep, syscall, SYS_alarm, SIGALRM};
+
+extern "C" fn handle_alarm(_: i32) {
+    println!("Alarm ring!");
+}
+
+fn main() {
+    // 设置信号处理函数
+    unsafe {
+        signal(SIGALRM, handle_alarm as usize);
+    }
+
+    //test1: alarm系统调用能否正常运行
+    unsafe {
+        syscall(SYS_alarm, 5);
+    }
+    println!("Alarm set for 5 seconds");
+    unsafe {
+        sleep(6);
+    }
+    println!("Test 1 complete");
+
+    //test2：在上一个alarm定时器未完成时重新调用alarm，查看返回值是否为上一个alarm的剩余秒数，
+    //并test第三个alarm定时器能否正常运行
+
+    unsafe {
+        let remaining = syscall(SYS_alarm, 5);
+        println!("Remaining time for previous alarm: {}", remaining);
+    }
+    println!("Alarm set for 5 seconds");
+    unsafe {
+        let remaining = syscall(SYS_alarm, 3);
+        println!("Remaining time for previous alarm: {}", remaining);
+    }
+    unsafe {
+        sleep(4);
+    }
+    println!("Alarm set for 3 seconds");
+
+    println!("Test 2 complete");
+}