Fix the thread status ordering by limiting the API

kernel/src/process/kill.rs

@@ -71,7 +71,7 @@ pub fn tgkill(tid: Tid, tgid: Pid, signal: Option<UserSignal>, ctx: &Context) ->
     let thread = thread_table::get_thread(tid)
         .ok_or_else(|| Error::with_message(Errno::ESRCH, "target thread does not exist"))?;
 
-    if thread.status().is_exited() {
+    if thread.is_exited() {
         return Ok(());
     }
 

kernel/src/process/posix_thread/exit.rs

@@ -14,7 +14,7 @@ use crate::{
 ///
 /// If the thread is not a POSIX thread, this method will panic.
 pub fn do_exit(thread: &Thread, posix_thread: &PosixThread, term_status: TermStatus) -> Result<()> {
-    if thread.status().is_exited() {
+    if thread.is_exited() {
         return Ok(());
     }
     thread.exit();

kernel/src/process/posix_thread/mod.rs

@@ -277,7 +277,7 @@ impl PosixThread {
         let tasks = process.tasks().lock();
         tasks
             .iter()
-            .all(|task| Thread::borrow_from_task(task).status().is_exited())
+            .all(|task| Thread::borrow_from_task(task).is_exited())
     }
 
     /// Gets the read-only credentials of the thread.

kernel/src/process/signal/mod.rs

@@ -31,7 +31,6 @@ use crate::{
     get_current_userspace,
     prelude::*,
     process::{do_exit_group, TermStatus},
-    thread::status::ThreadStatus,
 };
 
 pub trait SignalContext {
@@ -107,20 +106,10 @@ pub fn handle_pending_signal(user_ctx: &mut UserContext, ctx: &Context) -> Resul
                 }
                 SigDefaultAction::Ign => {}
                 SigDefaultAction::Stop => {
-                    let _ = ctx.thread.atomic_status().compare_exchange(
-                        ThreadStatus::Running,
-                        ThreadStatus::Stopped,
-                        Ordering::AcqRel,
-                        Ordering::Relaxed,
-                    );
+                    let _ = ctx.thread.stop();
                 }
                 SigDefaultAction::Cont => {
-                    let _ = ctx.thread.atomic_status().compare_exchange(
-                        ThreadStatus::Stopped,
-                        ThreadStatus::Running,
-                        Ordering::AcqRel,
-                        Ordering::Relaxed,
-                    );
+                    let _ = ctx.thread.resume();
                 }
             }
         }

kernel/src/thread/kernel_thread.rs

@@ -32,7 +32,7 @@ impl KernelThreadExt for Thread {
 
     fn join(&self) {
         loop {
-            if self.status().is_exited() {
+            if self.is_exited() {
                 return;
             } else {
                 Thread::yield_now();

kernel/src/thread/mod.rs

@@ -86,27 +86,59 @@ impl Thread {
 
     /// Runs this thread at once.
     pub fn run(&self) {
-        self.set_status(ThreadStatus::Running);
+        self.status.store(ThreadStatus::Running, Ordering::Release);
         self.task.upgrade().unwrap().run();
     }
 
+    /// Returns whether the thread is exited.
+    pub fn is_exited(&self) -> bool {
+        self.status.load(Ordering::Acquire).is_exited()
+    }
+
+    /// Returns whether the thread is stopped.
+    pub fn is_stopped(&self) -> bool {
+        self.status.load(Ordering::Acquire).is_stopped()
+    }
+
+    /// Stops the thread if it is running.
+    ///
+    /// If the previous status is not [`ThreadStatus::Running`], this function
+    /// returns [`Err`] with the previous state. Otherwise, it sets the status
+    /// to [`ThreadStatus::Stopped`] and returns [`Ok`] with the previous state.
+    ///
+    /// This function only sets the status to [`ThreadStatus::Stopped`],
+    /// without initiating a reschedule.
+    pub fn stop(&self) -> core::result::Result<ThreadStatus, ThreadStatus> {
+        self.status.compare_exchange(
+            ThreadStatus::Running,
+            ThreadStatus::Stopped,
+            Ordering::AcqRel,
+            Ordering::Acquire,
+        )
+    }
+
+    /// Resumes running the thread if it is stopped.
+    ///
+    /// If the previous status is not [`ThreadStatus::Stopped`], this function
+    /// returns [`None`]. Otherwise, it sets the status to
+    /// [`ThreadStatus::Running`] and returns [`Some(())`].
+    ///
+    /// This function only sets the status to [`ThreadStatus::Running`],
+    /// without initiating a reschedule.
+    pub fn resume(&self) -> Option<()> {
+        self.status
+            .compare_exchange(
+                ThreadStatus::Stopped,
+                ThreadStatus::Running,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            )
+            .ok()
+            .map(|_| ())
+    }
+
     pub(super) fn exit(&self) {
-        self.set_status(ThreadStatus::Exited);
-    }
-
-    /// Returns the reference to the atomic status.
-    pub fn atomic_status(&self) -> &AtomicThreadStatus {
-        &self.status
-    }
-
-    /// Returns the current status.
-    pub fn status(&self) -> ThreadStatus {
-        self.status.load(Ordering::Acquire)
-    }
-
-    /// Updates the status with the new value.
-    pub fn set_status(&self, new_status: ThreadStatus) {
-        self.status.store(new_status, Ordering::Release);
+        self.status.store(ThreadStatus::Exited, Ordering::Release);
     }
 
     /// Returns the reference to the atomic priority.
@@ -114,16 +146,6 @@ impl Thread {
         &self.priority
     }
 
-    /// Returns the current priority.
-    pub fn priority(&self) -> Priority {
-        self.priority.load(Ordering::Relaxed)
-    }
-
-    /// Updates the priority with the new value.
-    pub fn set_priority(&self, new_priority: Priority) {
-        self.priority.store(new_priority, Ordering::Relaxed)
-    }
-
     /// Returns the reference to the atomic CPU affinity.
     pub fn atomic_cpu_affinity(&self) -> &AtomicCpuSet {
         &self.cpu_affinity

kernel/src/thread/task.rs

@@ -71,17 +71,17 @@ pub fn create_new_user_task(user_space: Arc<UserSpace>, thread_ref: Arc<Thread>)
                 ReturnReason::KernelEvent => {}
             };
 
-            if current_thread.status().is_exited() {
+            if current_thread.is_exited() {
                 break;
             }
             handle_pending_signal(user_ctx, &ctx).unwrap();
             // If current is suspended, wait for a signal to wake up self
-            while current_thread.status().is_stopped() {
+            while current_thread.is_stopped() {
                 Thread::yield_now();
                 debug!("{} is suspended.", current_posix_thread.tid());
                 handle_pending_signal(user_ctx, &ctx).unwrap();
             }
-            if current_thread.status().is_exited() {
+            if current_thread.is_exited() {
                 debug!("exit due to signal");
                 break;
             }