diff --git a/core/src/lib.rs b/core/src/lib.rs
index 864dfb4527a9..f7b490f9dd62 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -153,7 +153,7 @@
 //! - [Performance Guide][crate::docs::performance]
 
 // Make sure all our public APIs have docs.
-#![warn(missing_docs)]
+#![deny(missing_docs)]
 
 // Private module with public types, they will be accessed via `opendal::Xxxx`
 mod types;
diff --git a/core/src/raw/futures_util.rs b/core/src/raw/futures_util.rs
index 44deab8d9016..1c6cd9386d18 100644
--- a/core/src/raw/futures_util.rs
+++ b/core/src/raw/futures_util.rs
@@ -25,19 +25,17 @@ use futures::FutureExt;
 use crate::*;
 
 /// BoxedFuture is the type alias of [`futures::future::BoxFuture`].
-///
-/// We will switch to [`futures::future::LocalBoxFuture`] on wasm32 target.
 #[cfg(not(target_arch = "wasm32"))]
 pub type BoxedFuture<'a, T> = futures::future::BoxFuture<'a, T>;
 #[cfg(target_arch = "wasm32")]
+/// BoxedFuture is the type alias of [`futures::future::LocalBoxFuture`].
 pub type BoxedFuture<'a, T> = futures::future::LocalBoxFuture<'a, T>;
 
 /// BoxedStaticFuture is the type alias of [`futures::future::BoxFuture`].
-///
-/// We will switch to [`futures::future::LocalBoxFuture`] on wasm32 target.
 #[cfg(not(target_arch = "wasm32"))]
 pub type BoxedStaticFuture<T> = futures::future::BoxFuture<'static, T>;
 #[cfg(target_arch = "wasm32")]
+/// BoxedStaticFuture is the type alias of [`futures::future::LocalBoxFuture`].
 pub type BoxedStaticFuture<T> = futures::future::LocalBoxFuture<'static, T>;
 
 /// MaybeSend is a marker to determine whether a type is `Send` or not.
@@ -49,6 +47,14 @@ pub type BoxedStaticFuture<T> = futures::future::LocalBoxFuture<'static, T>;
 /// And it's empty trait on wasm32 target to indicate that a type is not `Send`.
 #[cfg(not(target_arch = "wasm32"))]
 pub trait MaybeSend: Send {}
+
+/// MaybeSend is a marker to determine whether a type is `Send` or not.
+/// We use this trait to wrap the `Send` requirement for wasm32 target.
+///
+/// # Safety
+///
+/// [`MaybeSend`] is equivalent to `Send` on non-wasm32 target.
+/// And it's empty trait on wasm32 target to indicate that a type is not `Send`.
 #[cfg(target_arch = "wasm32")]
 pub trait MaybeSend {}
 
diff --git a/core/src/raw/oio/list/page_list.rs b/core/src/raw/oio/list/page_list.rs
index 2e146e33ce64..efdd826e3c23 100644
--- a/core/src/raw/oio/list/page_list.rs
+++ b/core/src/raw/oio/list/page_list.rs
@@ -36,6 +36,7 @@ pub trait PageList: Send + Sync + Unpin + 'static {
     #[cfg(not(target_arch = "wasm32"))]
     fn next_page(&self, ctx: &mut PageContext) -> impl Future<Output = Result<()>> + MaybeSend;
     #[cfg(target_arch = "wasm32")]
+    /// next_page is used to fetch next page of entries from underlying storage.
     fn next_page(&self, ctx: &mut PageContext) -> impl Future<Output = Result<()>>;
 }
 
diff --git a/core/src/types/read/reader.rs b/core/src/types/read/reader.rs
index 34e8cc67fb49..15c1cd46b1c8 100644
--- a/core/src/types/read/reader.rs
+++ b/core/src/types/read/reader.rs
@@ -20,10 +20,10 @@ use std::ops::RangeBounds;
 use std::sync::Arc;
 
 use bytes::BufMut;
-use futures::stream;
-use futures::StreamExt;
 use futures::TryStreamExt;
 
+use crate::raw::Access;
+use crate::raw::ConcurrentTasks;
 use crate::*;
 
 /// Reader is designed to read data from given path in an asynchronous
@@ -146,11 +146,32 @@ impl Reader {
     pub async fn fetch(&self, ranges: Vec<Range<u64>>) -> Result<Vec<Buffer>> {
         let merged_ranges = self.merge_ranges(ranges.clone());
 
-        let merged_bufs: Vec<_> =
-            stream::iter(merged_ranges.clone().into_iter().map(|v| self.read(v)))
-                .buffered(self.ctx.options().concurrent())
-                .try_collect()
-                .await?;
+        #[derive(Clone)]
+        struct FetchInput {
+            reader: Reader,
+            range: Range<u64>,
+        }
+
+        let mut tasks = ConcurrentTasks::new(
+            self.ctx.accessor().info().executor(),
+            self.ctx.options().concurrent(),
+            |input: FetchInput| {
+                Box::pin(async move {
+                    let FetchInput { range, reader } = input.clone();
+                    (input, reader.read(range).await)
+                })
+            },
+        );
+
+        for range in merged_ranges.clone() {
+            let reader = self.clone();
+            tasks.execute(FetchInput { reader, range }).await?;
+        }
+
+        let mut merged_bufs = vec![];
+        while let Some(b) = tasks.next().await {
+            merged_bufs.push(b?);
+        }
 
         let mut bufs = Vec::with_capacity(ranges.len());
         for range in ranges {