diff --git a/monoio-compat/src/lib.rs b/monoio-compat/src/lib.rs
index 39e87af0..209aa25b 100644
--- a/monoio-compat/src/lib.rs
+++ b/monoio-compat/src/lib.rs
@@ -1,7 +1,5 @@
 //! For compat with tokio AsyncRead and AsyncWrite.
 
-#![cfg_attr(feature = "unstable", feature(new_uninit))]
-
 pub mod box_future;
 mod buf;
 
diff --git a/monoio/src/blocking.rs b/monoio/src/blocking.rs
index 4e6bba7d..15dd49ce 100644
--- a/monoio/src/blocking.rs
+++ b/monoio/src/blocking.rs
@@ -287,44 +287,39 @@ mod tests {
 
     #[test]
     fn default_pool() {
-        let shared_pool = Box::new(DefaultThreadPool::new(3));
+        let shared_pool = Box::new(DefaultThreadPool::new(6));
         let mut rt = crate::RuntimeBuilder::<crate::FusionDriver>::new()
             .attach_thread_pool(shared_pool)
             .enable_timer()
             .build()
             .unwrap();
+        fn thread_sleep(s: &'static str) -> impl FnOnce() -> &'static str {
+            move || {
+                // Simulate a heavy computation.
+                std::thread::sleep(std::time::Duration::from_millis(500));
+                s
+            }
+        }
         rt.block_on(async {
             let begin = std::time::Instant::now();
-            let join1 = crate::spawn_blocking(|| {
-                // Simulate a heavy computation.
-                std::thread::sleep(std::time::Duration::from_millis(150));
-                "hello spawn_blocking1!".to_string()
-            });
-            let join2 = crate::spawn_blocking(|| {
-                // Simulate a heavy computation.
-                std::thread::sleep(std::time::Duration::from_millis(150));
-                "hello spawn_blocking2!".to_string()
-            });
-            let join3 = crate::spawn_blocking(|| {
-                // Simulate a heavy computation.
-                std::thread::sleep(std::time::Duration::from_millis(150));
-                "hello spawn_blocking3!".to_string()
-            });
-            let join4 = crate::spawn_blocking(|| {
-                // Simulate a heavy computation.
-                std::thread::sleep(std::time::Duration::from_millis(150));
-                "hello spawn_blocking4!".to_string()
-            });
-            let sleep_async = crate::time::sleep(std::time::Duration::from_millis(150));
-            let (result1, result2, result3, result4, _) =
-                crate::join!(join1, join2, join3, join4, sleep_async);
+            let join1 = crate::spawn_blocking(thread_sleep("hello spawn_blocking1!"));
+            let join2 = crate::spawn_blocking(thread_sleep("hello spawn_blocking2!"));
+            let join3 = crate::spawn_blocking(thread_sleep("hello spawn_blocking3!"));
+            let join4 = crate::spawn_blocking(thread_sleep("hello spawn_blocking4!"));
+            let join5 = crate::spawn_blocking(thread_sleep("hello spawn_blocking5!"));
+            let join6 = crate::spawn_blocking(thread_sleep("hello spawn_blocking6!"));
+            let sleep_async = crate::time::sleep(std::time::Duration::from_millis(500));
+            let (result1, result2, result3, result4, result5, result6, _) =
+                crate::join!(join1, join2, join3, join4, join5, join6, sleep_async);
             let eps = begin.elapsed();
-            assert!(eps < std::time::Duration::from_millis(590));
-            assert!(eps >= std::time::Duration::from_millis(150));
+            assert!(eps < std::time::Duration::from_millis(3000));
+            assert!(eps >= std::time::Duration::from_millis(500));
             assert_eq!(result1.unwrap(), "hello spawn_blocking1!");
             assert_eq!(result2.unwrap(), "hello spawn_blocking2!");
             assert_eq!(result3.unwrap(), "hello spawn_blocking3!");
             assert_eq!(result4.unwrap(), "hello spawn_blocking4!");
+            assert_eq!(result5.unwrap(), "hello spawn_blocking5!");
+            assert_eq!(result6.unwrap(), "hello spawn_blocking6!");
         });
     }
 }
diff --git a/monoio/src/buf/io_buf.rs b/monoio/src/buf/io_buf.rs
index 90c06be4..17515570 100644
--- a/monoio/src/buf/io_buf.rs
+++ b/monoio/src/buf/io_buf.rs
@@ -39,6 +39,12 @@ pub unsafe trait IoBuf: Unpin + 'static {
     /// For `Vec`, this is identical to `len()`.
     fn bytes_init(&self) -> usize;
 
+    /// Returns a slice of the buffer.
+    #[inline]
+    fn as_slice(&self) -> &[u8] {
+        unsafe { core::slice::from_raw_parts(self.read_ptr(), self.bytes_init()) }
+    }
+
     /// Returns a view of the buffer with the specified range.
     #[inline]
     fn slice(self, range: impl ops::RangeBounds<usize>) -> Slice<Self>
diff --git a/monoio/src/fs/file/mod.rs b/monoio/src/fs/file/mod.rs
index 6a457389..804b488f 100644
--- a/monoio/src/fs/file/mod.rs
+++ b/monoio/src/fs/file/mod.rs
@@ -505,8 +505,9 @@ impl File {
         Ok(())
     }
 
-    async fn flush(&mut self) -> io::Result<()> {
-        Ok(())
+    #[inline]
+    fn flush(&mut self) -> impl Future<Output = io::Result<()>> {
+        std::future::ready(Ok(()))
     }
 
     /// Closes the file.
diff --git a/monoio/src/io/async_read_rent.rs b/monoio/src/io/async_read_rent.rs
index 72843cff..1e3e215f 100644
--- a/monoio/src/io/async_read_rent.rs
+++ b/monoio/src/io/async_read_rent.rs
@@ -1,7 +1,7 @@
-use std::future::Future;
+use std::{future::Future, io::Cursor};
 
 use crate::{
-    buf::{IoBufMut, IoVecBufMut, RawBuf},
+    buf::{IoBufMut, IoVecBufMut},
     BufResult,
 };
 
@@ -49,6 +49,17 @@ pub trait AsyncReadRentAt {
     ) -> impl Future<Output = BufResult<usize, T>>;
 }
 
+impl<A: ?Sized + AsyncReadRentAt> AsyncReadRentAt for &mut A {
+    #[inline]
+    fn read_at<T: IoBufMut>(
+        &mut self,
+        buf: T,
+        pos: usize,
+    ) -> impl Future<Output = BufResult<usize, T>> {
+        (**self).read_at(buf, pos)
+    }
+}
+
 impl<A: ?Sized + AsyncReadRent> AsyncReadRent for &mut A {
     #[inline]
     fn read<T: IoBufMut>(&mut self, buf: T) -> impl Future<Output = BufResult<usize, T>> {
@@ -70,29 +81,85 @@ impl AsyncReadRent for &[u8] {
             buf.set_init(amt);
         }
         *self = b;
-        async move { (Ok(amt), buf) }
+        std::future::ready((Ok(amt), buf))
     }
 
     fn readv<T: IoVecBufMut>(&mut self, mut buf: T) -> impl Future<Output = BufResult<usize, T>> {
-        // # Safety
-        // We do it in pure sync way.
-        let n = match unsafe { RawBuf::new_from_iovec_mut(&mut buf) } {
-            Some(mut raw_buf) => {
-                // copy from read to avoid await
-                let amt = std::cmp::min(self.len(), raw_buf.bytes_total());
+        let mut sum = 0;
+        {
+            #[cfg(windows)]
+            let buf_slice = unsafe {
+                std::slice::from_raw_parts_mut(buf.write_wsabuf_ptr(), buf.write_wsabuf_len())
+            };
+            #[cfg(unix)]
+            let buf_slice = unsafe {
+                std::slice::from_raw_parts_mut(buf.write_iovec_ptr(), buf.write_iovec_len())
+            };
+            for buf in buf_slice {
+                #[cfg(windows)]
+                let amt = std::cmp::min(self.len(), buf.len as usize);
+                #[cfg(unix)]
+                let amt = std::cmp::min(self.len(), buf.iov_len);
+
                 let (a, b) = self.split_at(amt);
+                // # Safety
+                // The pointer is valid.
                 unsafe {
-                    raw_buf
-                        .write_ptr()
+                    #[cfg(windows)]
+                    buf.buf
+                        .cast::<u8>()
+                        .copy_from_nonoverlapping(a.as_ptr(), amt);
+                    #[cfg(unix)]
+                    buf.iov_base
+                        .cast::<u8>()
                         .copy_from_nonoverlapping(a.as_ptr(), amt);
-                    raw_buf.set_init(amt);
                 }
                 *self = b;
-                amt
+                sum += amt;
+
+                if self.is_empty() {
+                    break;
+                }
             }
-            None => 0,
-        };
-        unsafe { buf.set_init(n) };
-        async move { (Ok(n), buf) }
+        }
+
+        unsafe { buf.set_init(sum) };
+        std::future::ready((Ok(sum), buf))
+    }
+}
+
+impl<T: AsRef<[u8]>> AsyncReadRent for Cursor<T> {
+    async fn read<B: IoBufMut>(&mut self, buf: B) -> BufResult<usize, B> {
+        let pos = self.position();
+        let slice: &[u8] = (*self).get_ref().as_ref();
+
+        if pos > slice.len() as u64 {
+            return (Ok(0), buf);
+        }
+
+        (&slice[pos as usize..]).read(buf).await
+    }
+
+    async fn readv<B: IoVecBufMut>(&mut self, buf: B) -> BufResult<usize, B> {
+        let pos = self.position();
+        let slice: &[u8] = (*self).get_ref().as_ref();
+
+        if pos > slice.len() as u64 {
+            return (Ok(0), buf);
+        }
+
+        (&slice[pos as usize..]).readv(buf).await
+    }
+}
+
+impl<T: ?Sized + AsyncReadRent> AsyncReadRent for Box<T> {
+    #[inline]
+    fn read<B: IoBufMut>(&mut self, buf: B) -> impl Future<Output = BufResult<usize, B>> {
+        (**self).read(buf)
+    }
+
+    #[inline]
+    fn readv<B: IoVecBufMut>(&mut self, buf: B) -> impl Future<Output = BufResult<usize, B>> {
+        (**self).readv(buf)
     }
 }
diff --git a/monoio/src/io/async_write_rent.rs b/monoio/src/io/async_write_rent.rs
index 482f1945..17551030 100644
--- a/monoio/src/io/async_write_rent.rs
+++ b/monoio/src/io/async_write_rent.rs
@@ -83,6 +83,17 @@ pub trait AsyncWriteRentAt {
     ) -> impl Future<Output = BufResult<usize, T>>;
 }
 
+impl<A: ?Sized + AsyncWriteRentAt> AsyncWriteRentAt for &mut A {
+    #[inline]
+    fn write_at<T: IoBuf>(
+        &mut self,
+        buf: T,
+        pos: usize,
+    ) -> impl Future<Output = BufResult<usize, T>> {
+        (**self).write_at(buf, pos)
+    }
+}
+
 impl<A: ?Sized + AsyncWriteRent> AsyncWriteRent for &mut A {
     #[inline]
     fn write<T: IoBuf>(&mut self, buf: T) -> impl Future<Output = BufResult<usize, T>> {
@@ -104,3 +115,56 @@ impl<A: ?Sized + AsyncWriteRent> AsyncWriteRent for &mut A {
         (**self).shutdown()
     }
 }
+
+impl AsyncWriteRent for Vec<u8> {
+    fn write<T: IoBuf>(&mut self, buf: T) -> impl Future<Output = BufResult<usize, T>> {
+        let slice = buf.as_slice();
+        self.extend_from_slice(slice);
+        let len = slice.len();
+        std::future::ready((Ok(len), buf))
+    }
+
+    fn writev<T: IoVecBuf>(&mut self, buf: T) -> impl Future<Output = BufResult<usize, T>> {
+        let mut sum = 0;
+        {
+            #[cfg(windows)]
+            let buf_slice =
+                unsafe { std::slice::from_raw_parts(buf.read_wsabuf_ptr(), buf.read_wsabuf_len()) };
+            #[cfg(unix)]
+            let buf_slice =
+                unsafe { std::slice::from_raw_parts(buf.read_iovec_ptr(), buf.read_iovec_len()) };
+            for buf in buf_slice {
+                #[cfg(windows)]
+                let len = buf.len as usize;
+                #[cfg(unix)]
+                let len = buf.iov_len;
+
+                sum += len;
+            }
+            self.reserve(sum);
+            for buf in buf_slice {
+                #[cfg(windows)]
+                let ptr = buf.buf.cast::<u8>();
+                #[cfg(unix)]
+                let ptr = buf.iov_base.cast::<u8>();
+                #[cfg(windows)]
+                let len = buf.len as usize;
+                #[cfg(unix)]
+                let len = buf.iov_len;
+
+                self.extend_from_slice(unsafe { std::slice::from_raw_parts(ptr, len) });
+            }
+        }
+        std::future::ready((Ok(sum), buf))
+    }
+
+    #[inline]
+    fn flush(&mut self) -> impl Future<Output = std::io::Result<()>> {
+        std::future::ready(Ok(()))
+    }
+
+    #[inline]
+    fn shutdown(&mut self) -> impl Future<Output = std::io::Result<()>> {
+        std::future::ready(Ok(()))
+    }
+}
diff --git a/monoio/src/net/tcp/stream.rs b/monoio/src/net/tcp/stream.rs
index 36eb1ae3..19978767 100644
--- a/monoio/src/net/tcp/stream.rs
+++ b/monoio/src/net/tcp/stream.rs
@@ -331,9 +331,9 @@ impl AsyncWriteRent for TcpStream {
     }
 
     #[inline]
-    async fn flush(&mut self) -> std::io::Result<()> {
+    fn flush(&mut self) -> impl Future<Output = std::io::Result<()>> {
         // Tcp stream does not need flush.
-        Ok(())
+        std::future::ready(Ok(()))
     }
 
     fn shutdown(&mut self) -> impl Future<Output = std::io::Result<()>> {
@@ -347,7 +347,7 @@ impl AsyncWriteRent for TcpStream {
             -1 => Err(io::Error::last_os_error()),
             _ => Ok(()),
         };
-        async move { res }
+        std::future::ready(res)
     }
 }
 
@@ -403,7 +403,7 @@ impl CancelableAsyncWriteRent for TcpStream {
             -1 => Err(io::Error::last_os_error()),
             _ => Ok(()),
         };
-        async move { res }
+        std::future::ready(res)
     }
 }