diff --git a/services/libs/jinux-std/src/events/events.rs b/services/libs/jinux-std/src/events/events.rs
index 002197d48..9488b0033 100644
--- a/services/libs/jinux-std/src/events/events.rs
+++ b/services/libs/jinux-std/src/events/events.rs
@@ -1,2 +1,34 @@
 /// A trait to represent any events.
 pub trait Events: Copy + Clone + Send + Sync + 'static {}
+
+/// A trait to filter events.
+///
+/// # The no-op event filter
+///
+/// The unit type `()` can serve as a no-op event filter.
+/// It implements `EventsFilter<E>` for any events type `E`,
+/// with a `filter` method that always returns `true`.
+/// If the `F` type of `Subject<E, F>` is not specified explicitly,
+/// then the unit type `()` is chosen as the event filter.
+///
+/// # Per-object event filter
+///
+/// Any `Option<F: EventsFilter>` is also an event filter thanks to
+/// the blanket implementations the `EventsFilter` trait.
+/// By using `Option<F: EventsFilter>`, we can decide, on a per-observer basis,
+/// if an observer needs an event filter.
+pub trait EventsFilter<E: Events>: Send + Sync + 'static {
+    fn filter(&self, event: &E) -> bool;
+}
+
+impl<E: Events> EventsFilter<E> for () {
+    fn filter(&self, _events: &E) -> bool {
+        true
+    }
+}
+
+impl<E: Events, F: EventsFilter<E>> EventsFilter<E> for Option<F> {
+    fn filter(&self, events: &E) -> bool {
+        self.as_ref().map_or(true, |f| f.filter(events))
+    }
+}
diff --git a/services/libs/jinux-std/src/events/mod.rs b/services/libs/jinux-std/src/events/mod.rs
index 18e154e93..10f4421e5 100644
--- a/services/libs/jinux-std/src/events/mod.rs
+++ b/services/libs/jinux-std/src/events/mod.rs
@@ -2,6 +2,6 @@ mod events;
 mod observer;
 mod subject;
 
-pub use self::events::Events;
+pub use self::events::{Events, EventsFilter};
 pub use self::observer::Observer;
 pub use self::subject::Subject;
diff --git a/services/libs/jinux-std/src/events/subject.rs b/services/libs/jinux-std/src/events/subject.rs
index 56ab957e7..54dfc2d22 100644
--- a/services/libs/jinux-std/src/events/subject.rs
+++ b/services/libs/jinux-std/src/events/subject.rs
@@ -1,43 +1,86 @@
 use crate::prelude::*;
 
-use super::{Events, Observer};
+use core::sync::atomic::{AtomicUsize, Ordering};
+use keyable_arc::KeyableWeak;
 
-/// A Subject notify interesting events to registered observers.
-pub struct Subject<E: Events> {
-    observers: Mutex<Vec<Weak<dyn Observer<E>>>>,
+use super::{Events, EventsFilter, Observer};
+
+/// A Subject notifies interesting events to registered observers.
+pub struct Subject<E: Events, F: EventsFilter<E> = ()> {
+    // A table that maintains all interesting observers.
+    observers: Mutex<BTreeMap<KeyableWeak<dyn Observer<E>>, F>>,
+    // To reduce lock contentions, we maintain a counter for the size of the table
+    num_observers: AtomicUsize,
 }
 
-impl<E: Events> Subject<E> {
+impl<E: Events, F: EventsFilter<E>> Subject<E, F> {
     pub fn new() -> Self {
         Self {
-            observers: Mutex::new(Vec::new()),
+            observers: Mutex::new(BTreeMap::new()),
+            num_observers: AtomicUsize::new(0),
         }
     }
 
     /// Register an observer.
-    pub fn register_observer(&self, observer: Weak<dyn Observer<E>>) {
+    ///
+    /// A registered observer will get notified through its `on_events` method.
+    /// If events `filter` is provided, only filtered events will notify the observer.
+    ///
+    /// If the given observer has already been registered, then its registered events
+    /// filter will be updated.
+    pub fn register_observer(&self, observer: Weak<dyn Observer<E>>, filter: F) {
         let mut observers = self.observers.lock();
-        observers.push(observer);
+        let is_new = {
+            let observer: KeyableWeak<dyn Observer<E>> = observer.into();
+            observers.insert(observer, filter).is_none()
+        };
+        if is_new {
+            self.num_observers.fetch_add(1, Ordering::Release);
+        }
     }
 
     /// Unregister an observer.
-    pub fn unregister_observer(&self, observer: &Weak<dyn Observer<E>>) {
+    ///
+    /// If such an observer is found, then the registered observer will be
+    /// removed from the subject and returned as the return value. Otherwise,
+    /// a `None` will be returned.
+    pub fn unregister_observer(
+        &self,
+        observer: &Weak<dyn Observer<E>>,
+    ) -> Option<Weak<dyn Observer<E>>> {
+        let observer: KeyableWeak<dyn Observer<E>> = observer.clone().into();
         let mut observers = self.observers.lock();
-        observers.retain(|e| !Weak::ptr_eq(&e, observer));
+        let observer = observers
+            .remove_entry(&observer)
+            .map(|(observer, _)| observer.into());
+        if observer.is_some() {
+            self.num_observers.fetch_sub(1, Ordering::Relaxed);
+        }
+        observer
     }
 
     /// Notify events to all registered observers.
+    ///
     /// It will remove the observers which have been freed.
     pub fn notify_observers(&self, events: &E) {
-        let mut observers = self.observers.lock();
-        let mut idx = 0;
-        while idx < observers.len() {
-            if let Some(observer) = observers[idx].upgrade() {
-                observer.on_events(events);
-                idx += 1;
-            } else {
-                observers.remove(idx);
-            }
+        // Fast path.
+        if self.num_observers.load(Ordering::Relaxed) == 0 {
+            return;
         }
+
+        // Slow path: broadcast the new events to all observers.
+        let mut observers = self.observers.lock();
+        observers.retain(|observer, filter| {
+            if let Some(observer) = observer.upgrade() {
+                if !filter.filter(events) {
+                    return true;
+                }
+                observer.on_events(events);
+                true
+            } else {
+                self.num_observers.fetch_sub(1, Ordering::Relaxed);
+                false
+            }
+        });
     }
 }
diff --git a/services/libs/jinux-std/src/fs/epoll/epoll_file.rs b/services/libs/jinux-std/src/fs/epoll/epoll_file.rs
index a3d0279d8..6df757ae9 100644
--- a/services/libs/jinux-std/src/fs/epoll/epoll_file.rs
+++ b/services/libs/jinux-std/src/fs/epoll/epoll_file.rs
@@ -76,7 +76,7 @@ impl EpollFile {
         if interest.contains_key(&fd) {
             return_errno_with_message!(Errno::EEXIST, "the fd has been added");
         }
-        file.register_observer(entry.clone(), IoEvents::all())?;
+        file.register_observer(entry.self_weak() as _, IoEvents::all())?;
         interest.insert(fd, entry.clone());
         // Register self to the file table entry
         file_table_entry.register_observer(self.weak_self.clone() as _);
@@ -113,7 +113,7 @@ impl EpollFile {
             None => return Ok(()),
         };
 
-        file.unregister_observer(&(entry as _)).unwrap();
+        file.unregister_observer(&(entry.self_weak() as _)).unwrap();
         Ok(())
     }
 
@@ -294,7 +294,7 @@ impl Drop for EpollFile {
             .map(|(fd, entry)| {
                 entry.set_deleted();
                 if let Some(file) = entry.file() {
-                    let _ = file.unregister_observer(&(entry as _));
+                    let _ = file.unregister_observer(&(entry.self_weak() as _));
                 }
                 fd
             })
@@ -326,7 +326,7 @@ impl FileLike for EpollFile {
 
     fn register_observer(
         &self,
-        observer: Arc<dyn Observer<IoEvents>>,
+        observer: Weak<dyn Observer<IoEvents>>,
         mask: IoEvents,
     ) -> Result<()> {
         self.pollee.register_observer(observer, mask);
@@ -335,8 +335,8 @@ impl FileLike for EpollFile {
 
     fn unregister_observer(
         &self,
-        observer: &Arc<dyn Observer<IoEvents>>,
-    ) -> Result<Arc<dyn Observer<IoEvents>>> {
+        observer: &Weak<dyn Observer<IoEvents>>,
+    ) -> Result<Weak<dyn Observer<IoEvents>>> {
         self.pollee
             .unregister_observer(observer)
             .ok_or_else(|| Error::with_message(Errno::ENOENT, "observer is not registered"))
@@ -398,6 +398,11 @@ impl EpollEntry {
         self.weak_self.upgrade().unwrap()
     }
 
+    /// Get an instance of `Weak` that refers to this epoll entry.
+    pub fn self_weak(&self) -> Weak<Self> {
+        self.weak_self.clone()
+    }
+
     /// Get the file associated with this epoll entry.
     ///
     /// Since an epoll entry only holds a weak reference to the file,
diff --git a/services/libs/jinux-std/src/fs/file_handle.rs b/services/libs/jinux-std/src/fs/file_handle.rs
index 6f3709ab2..e08841e7c 100644
--- a/services/libs/jinux-std/src/fs/file_handle.rs
+++ b/services/libs/jinux-std/src/fs/file_handle.rs
@@ -51,7 +51,7 @@ pub trait FileLike: Send + Sync + Any {
 
     fn register_observer(
         &self,
-        observer: Arc<dyn Observer<IoEvents>>,
+        observer: Weak<dyn Observer<IoEvents>>,
         mask: IoEvents,
     ) -> Result<()> {
         return_errno_with_message!(Errno::EINVAL, "register_observer is not supported")
@@ -59,8 +59,8 @@ pub trait FileLike: Send + Sync + Any {
 
     fn unregister_observer(
         &self,
-        observer: &Arc<dyn Observer<IoEvents>>,
-    ) -> Result<Arc<dyn Observer<IoEvents>>> {
+        observer: &Weak<dyn Observer<IoEvents>>,
+    ) -> Result<Weak<dyn Observer<IoEvents>>> {
         return_errno_with_message!(Errno::EINVAL, "unregister_observer is not supported")
     }
 
diff --git a/services/libs/jinux-std/src/fs/file_table.rs b/services/libs/jinux-std/src/fs/file_table.rs
index d52be7575..8964cfb5f 100644
--- a/services/libs/jinux-std/src/fs/file_table.rs
+++ b/services/libs/jinux-std/src/fs/file_table.rs
@@ -114,7 +114,7 @@ impl FileTable {
     }
 
     pub fn register_observer(&self, observer: Weak<dyn Observer<FdEvents>>) {
-        self.subject.register_observer(observer);
+        self.subject.register_observer(observer, ());
     }
 
     pub fn unregister_observer(&self, observer: &Weak<dyn Observer<FdEvents>>) {
@@ -170,7 +170,7 @@ impl FileTableEntry {
     }
 
     pub fn register_observer(&self, epoll: Weak<dyn Observer<FdEvents>>) {
-        self.subject.register_observer(epoll);
+        self.subject.register_observer(epoll, ());
     }
 
     pub fn unregister_observer(&self, epoll: &Weak<dyn Observer<FdEvents>>) {
diff --git a/services/libs/jinux-std/src/fs/pipe.rs b/services/libs/jinux-std/src/fs/pipe.rs
index 4e0aa345d..feedfc8cb 100644
--- a/services/libs/jinux-std/src/fs/pipe.rs
+++ b/services/libs/jinux-std/src/fs/pipe.rs
@@ -45,7 +45,7 @@ impl FileLike for PipeReader {
 
     fn register_observer(
         &self,
-        observer: Arc<dyn Observer<IoEvents>>,
+        observer: Weak<dyn Observer<IoEvents>>,
         mask: IoEvents,
     ) -> Result<()> {
         self.consumer.register_observer(observer, mask)
@@ -53,8 +53,8 @@ impl FileLike for PipeReader {
 
     fn unregister_observer(
         &self,
-        observer: &Arc<dyn Observer<IoEvents>>,
-    ) -> Result<Arc<dyn Observer<IoEvents>>> {
+        observer: &Weak<dyn Observer<IoEvents>>,
+    ) -> Result<Weak<dyn Observer<IoEvents>>> {
         self.consumer.unregister_observer(observer)
     }
 
@@ -104,7 +104,7 @@ impl FileLike for PipeWriter {
 
     fn register_observer(
         &self,
-        observer: Arc<dyn Observer<IoEvents>>,
+        observer: Weak<dyn Observer<IoEvents>>,
         mask: IoEvents,
     ) -> Result<()> {
         self.producer.register_observer(observer, mask)
@@ -112,8 +112,8 @@ impl FileLike for PipeWriter {
 
     fn unregister_observer(
         &self,
-        observer: &Arc<dyn Observer<IoEvents>>,
-    ) -> Result<Arc<dyn Observer<IoEvents>>> {
+        observer: &Weak<dyn Observer<IoEvents>>,
+    ) -> Result<Weak<dyn Observer<IoEvents>>> {
         self.producer.unregister_observer(observer)
     }
 
diff --git a/services/libs/jinux-std/src/fs/utils/channel.rs b/services/libs/jinux-std/src/fs/utils/channel.rs
index 02deda2b9..ed8448b0b 100644
--- a/services/libs/jinux-std/src/fs/utils/channel.rs
+++ b/services/libs/jinux-std/src/fs/utils/channel.rs
@@ -83,7 +83,7 @@ macro_rules! impl_common_methods_for_channel {
 
         pub fn register_observer(
             &self,
-            observer: Arc<dyn Observer<IoEvents>>,
+            observer: Weak<dyn Observer<IoEvents>>,
             mask: IoEvents,
         ) -> Result<()> {
             self.this_end().pollee.register_observer(observer, mask);
@@ -92,8 +92,8 @@ macro_rules! impl_common_methods_for_channel {
 
         pub fn unregister_observer(
             &self,
-            observer: &Arc<dyn Observer<IoEvents>>,
-        ) -> Result<Arc<dyn Observer<IoEvents>>> {
+            observer: &Weak<dyn Observer<IoEvents>>,
+        ) -> Result<Weak<dyn Observer<IoEvents>>> {
             self.this_end()
                 .pollee
                 .unregister_observer(observer)
diff --git a/services/libs/jinux-std/src/fs/utils/io_events.rs b/services/libs/jinux-std/src/fs/utils/io_events.rs
index 4a3cbe41a..7d5ed3c43 100644
--- a/services/libs/jinux-std/src/fs/utils/io_events.rs
+++ b/services/libs/jinux-std/src/fs/utils/io_events.rs
@@ -1,4 +1,4 @@
-use crate::events::Events;
+use crate::events::{Events, EventsFilter};
 
 crate::bitflags! {
     pub struct IoEvents: u32 {
@@ -15,3 +15,9 @@ crate::bitflags! {
 }
 
 impl Events for IoEvents {}
+
+impl EventsFilter<IoEvents> for IoEvents {
+    fn filter(&self, events: &IoEvents) -> bool {
+        self.intersects(*events)
+    }
+}
diff --git a/services/libs/jinux-std/src/fs/utils/poll.rs b/services/libs/jinux-std/src/fs/utils/poll.rs
index 905e0a3be..9a1a37f2d 100644
--- a/services/libs/jinux-std/src/fs/utils/poll.rs
+++ b/services/libs/jinux-std/src/fs/utils/poll.rs
@@ -1,10 +1,10 @@
 use super::IoEvents;
-use crate::events::Observer;
+use crate::events::{Observer, Subject};
 use crate::prelude::*;
 
 use core::sync::atomic::{AtomicU32, AtomicUsize, Ordering};
 use jinux_frame::sync::WaitQueue;
-use keyable_arc::KeyableArc;
+use keyable_arc::KeyableWeak;
 
 /// A pollee maintains a set of active events, which can be polled with
 /// pollers or be monitored with observers.
@@ -13,21 +13,18 @@ pub struct Pollee {
 }
 
 struct PolleeInner {
-    // A table that maintains all interesting pollers
-    pollers: Mutex<BTreeMap<KeyableArc<dyn Observer<IoEvents>>, IoEvents>>,
-    // For efficient manipulation, we use AtomicU32 instead of RwLock<IoEvents>
+    // A subject which is monitored with pollers.
+    subject: Subject<IoEvents, IoEvents>,
+    // For efficient manipulation, we use AtomicU32 instead of RwLock<IoEvents>.
     events: AtomicU32,
-    // To reduce lock contentions, we maintain a counter for the size of the table
-    num_pollers: AtomicUsize,
 }
 
 impl Pollee {
     /// Creates a new instance of pollee.
     pub fn new(init_events: IoEvents) -> Self {
         let inner = PolleeInner {
-            pollers: Mutex::new(BTreeMap::new()),
+            subject: Subject::new(),
             events: AtomicU32::new(init_events.bits()),
-            num_pollers: AtomicUsize::new(0),
         };
         Self {
             inner: Arc::new(inner),
@@ -51,7 +48,7 @@ impl Pollee {
             return revents;
         }
 
-        // Slow path: register the provided poller
+        // Register the provided poller.
         self.register_poller(poller.unwrap(), mask);
 
         // It is important to check events again to handle race conditions
@@ -60,17 +57,11 @@ impl Pollee {
     }
 
     fn register_poller(&self, poller: &Poller, mask: IoEvents) {
-        let mut pollers = self.inner.pollers.lock();
-        let is_new = {
-            let observer = poller.observer();
-            pollers.insert(observer, mask).is_none()
-        };
-        if is_new {
-            let mut pollees = poller.inner.pollees.lock();
-            pollees.push(Arc::downgrade(&self.inner));
-
-            self.inner.num_pollers.fetch_add(1, Ordering::Release);
-        }
+        self.inner
+            .subject
+            .register_observer(poller.observer(), mask);
+        let mut pollees = poller.inner.pollees.lock();
+        pollees.insert(Arc::downgrade(&self.inner).into(), ());
     }
 
     /// Register an IoEvents observer.
@@ -84,23 +75,9 @@ impl Pollee {
     ///
     /// Note that the observer will always get notified of the events in
     /// `IoEvents::ALWAYS_POLL` regardless of the value of `mask`.
-    ///
-    /// # Memory leakage
-    ///
-    /// Since an `Arc` for each observer is kept internally by a pollee,
-    /// it is important for the user to call the `unregister_observer` method
-    /// when the observer is no longer interested in the pollee. Otherwise,
-    /// the observer will not be dropped.
-    pub fn register_observer(&self, observer: Arc<dyn Observer<IoEvents>>, mask: IoEvents) {
-        let mut pollers = self.inner.pollers.lock();
-        let is_new = {
-            let observer: KeyableArc<dyn Observer<IoEvents>> = observer.into();
-            let mask = mask | IoEvents::ALWAYS_POLL;
-            pollers.insert(observer, mask).is_none()
-        };
-        if is_new {
-            self.inner.num_pollers.fetch_add(1, Ordering::Release);
-        }
+    pub fn register_observer(&self, observer: Weak<dyn Observer<IoEvents>>, mask: IoEvents) {
+        let mask = mask | IoEvents::ALWAYS_POLL;
+        self.inner.subject.register_observer(observer, mask);
     }
 
     /// Unregister an IoEvents observer.
@@ -110,17 +87,9 @@ impl Pollee {
     /// a `None` will be returned.
     pub fn unregister_observer(
         &self,
-        observer: &Arc<dyn Observer<IoEvents>>,
-    ) -> Option<Arc<dyn Observer<IoEvents>>> {
-        let observer: KeyableArc<dyn Observer<IoEvents>> = observer.clone().into();
-        let mut pollers = self.inner.pollers.lock();
-        let observer = pollers
-            .remove_entry(&observer)
-            .map(|(observer, _)| observer.into());
-        if observer.is_some() {
-            self.inner.num_pollers.fetch_sub(1, Ordering::Relaxed);
-        }
-        observer
+        observer: &Weak<dyn Observer<IoEvents>>,
+    ) -> Option<Weak<dyn Observer<IoEvents>>> {
+        self.inner.subject.unregister_observer(observer)
     }
 
     /// Add some events to the pollee's state.
@@ -129,18 +98,7 @@ impl Pollee {
     /// the added events.
     pub fn add_events(&self, events: IoEvents) {
         self.inner.events.fetch_or(events.bits(), Ordering::Release);
-
-        // Fast path
-        if self.inner.num_pollers.load(Ordering::Relaxed) == 0 {
-            return;
-        }
-
-        // Slow path: broadcast the new events to all pollers
-        let pollers = self.inner.pollers.lock();
-        pollers
-            .iter()
-            .filter(|(_, mask)| mask.intersects(events))
-            .for_each(|(poller, mask)| poller.on_events(&(events & *mask)));
+        self.inner.subject.notify_observers(&events);
     }
 
     /// Remove some events from the pollee's state.
@@ -170,14 +128,14 @@ impl Pollee {
 
 /// A poller gets notified when its associated pollees have interesting events.
 pub struct Poller {
-    inner: KeyableArc<PollerInner>,
+    inner: Arc<PollerInner>,
 }
 
 struct PollerInner {
     // Use event counter to wait or wake up a poller
     event_counter: EventCounter,
     // All pollees that are interesting to this poller
-    pollees: Mutex<Vec<Weak<PolleeInner>>>,
+    pollees: Mutex<BTreeMap<KeyableWeak<PolleeInner>, ()>>,
 }
 
 impl Poller {
@@ -185,10 +143,10 @@ impl Poller {
     pub fn new() -> Self {
         let inner = PollerInner {
             event_counter: EventCounter::new(),
-            pollees: Mutex::new(Vec::with_capacity(1)),
+            pollees: Mutex::new(BTreeMap::new()),
         };
         Self {
-            inner: KeyableArc::new(inner),
+            inner: Arc::new(inner),
         }
     }
 
@@ -197,8 +155,8 @@ impl Poller {
         self.inner.event_counter.read();
     }
 
-    fn observer(&self) -> KeyableArc<dyn Observer<IoEvents>> {
-        self.inner.clone() as KeyableArc<dyn Observer<IoEvents>>
+    fn observer(&self) -> Weak<dyn Observer<IoEvents>> {
+        Arc::downgrade(&self.inner) as _
     }
 }
 
@@ -216,14 +174,9 @@ impl Drop for Poller {
         }
 
         let self_observer = self.observer();
-        for weak_pollee in pollees.drain(..) {
+        for (weak_pollee, _) in pollees.drain_filter(|_, _| true) {
             if let Some(pollee) = weak_pollee.upgrade() {
-                let mut pollers = pollee.pollers.lock();
-                let res = pollers.remove(&self_observer);
-                assert!(res.is_some());
-                drop(pollers);
-
-                pollee.num_pollers.fetch_sub(1, Ordering::Relaxed);
+                pollee.subject.unregister_observer(&self_observer);
             }
         }
     }
diff --git a/services/libs/jinux-std/src/process/process_table.rs b/services/libs/jinux-std/src/process/process_table.rs
index 69c4400db..50a693a8e 100644
--- a/services/libs/jinux-std/src/process/process_table.rs
+++ b/services/libs/jinux-std/src/process/process_table.rs
@@ -65,7 +65,7 @@ pub fn pgid_to_process_group(pgid: Pgid) -> Option<Arc<ProcessGroup>> {
 }
 
 pub fn register_observer(observer: Weak<dyn Observer<PidEvent>>) {
-    PROCESS_TABLE_SUBJECT.register_observer(observer);
+    PROCESS_TABLE_SUBJECT.register_observer(observer, ());
 }
 
 pub fn unregister_observer(observer: &Weak<dyn Observer<PidEvent>>) {