[Semaphore] Optimize the update_pending_ops

kernel/src/ipc/semaphore/system_v/sem.rs

@@ -258,37 +258,43 @@ impl Semaphore {
         // 2. If val is equal to 0, then clear pending_const
 
         // Step one:
+        let mut value = *val;
+        if value > 0 {
             let mut pending_alters = self.pending_alters.lock();
-        pending_alters.retain_mut(|op| {
-            if *val == 0 {
-                return true;
+            let mut cursor = pending_alters.cursor_front_mut();
+            while let Some(op) = cursor.current() {
+                if value == 0 {
+                    break;
                 }
                 // Check if the process alive.
                 if op.process.upgrade().is_none() {
-                return false;
+                    cursor.remove_current().unwrap();
+                    continue;
                 }
+
                 debug_assert!(op.sem_buf.sem_op < 0);
 
-            if op.sem_buf.sem_op.abs() as i32 <= *val {
+                if op.sem_buf.sem_op.abs() as i32 <= value {
                     trace!(
                         "Found removable pending op, op: {:?}, pid:{:?}",
                         op.sem_buf.sem_op,
                         op.pid
                     );
 
-                *val += i32::from(op.sem_buf.sem_op);
+                    value += i32::from(op.sem_buf.sem_op);
                     self.latest_modified_pid.store(op.pid, Ordering::Relaxed);
                     self.update_otime();
                     op.status.set_status(Status::Normal);
                     op.waker.wake_up();
-                false
+                    cursor.remove_current().unwrap();
                 } else {
-                true
+                    cursor.move_next();
+                }
+            }
         }
-        });
 
         // Step two:
-        if *val == 0 {
+        if value == 0 {
             let mut pending_const = self.pending_const.lock();
             pending_const.iter().for_each(|op| {
                 op.status.set_status(Status::Normal);
@@ -299,7 +305,8 @@ impl Semaphore {
             });
             pending_const.clear();
         }
-        trace!("Updated pending ops, semaphore after: {:?}", *val);
+        *val = value;
+        trace!("Updated pending ops, semaphore after: {:?}", value);
     }
 }
 

kernel/src/lib.rs

@@ -28,6 +28,7 @@
 #![feature(trait_alias)]
 #![feature(trait_upcasting)]
 #![feature(linked_list_retain)]
+#![feature(linked_list_cursors)]
 #![register_tool(component_access_control)]
 
 use core::sync::atomic::Ordering;