chore: add warning to block_on

Should this become an unsafe function?

Signed-off-by: Tiago Castro <tiagolobocastro@gmail.com>

Author: tiagolobocastro

io-engine/src/bdev/nexus/nexus_bdev.rs

@@ -1373,30 +1373,38 @@ impl<'n> BdevOps for Nexus<'n> {
             return;
         }
 
-        let self_ptr = unsafe { unsafe_static_ptr(&self) };
-
-        Reactor::block_on(async move {
-            let self_ref = unsafe { &mut *self_ptr };
-
-            // TODO: double-check interaction with rebuild job logic
-            // TODO: cancel rebuild jobs?
-            let n = self_ref.children.iter().filter(|c| c.is_opened()).count();
-
-            if n > 0 {
-                warn!(
-                    "{:?}: {} open children remain(s), closing...",
-                    self_ref, n
-                );
+        let open_children =
+            self.children.iter().filter(|c| c.is_opened()).count();
+        // TODO: This doesn't seem possible to happen at this stage, but seems
+        // we should still try to handle this in separate future since
+        // we're handling it here anyway as a block_on is not safe to
+        // use for running production code.
+        if open_children > 0 {
+            let self_ptr = unsafe { unsafe_static_ptr(&self) };
+            Reactor::block_on(async move {
+                let self_ref = unsafe { &mut *self_ptr };
+
+                // TODO: double-check interaction with rebuild job logic
+                // TODO: cancel rebuild jobs?
+                let n =
+                    self_ref.children.iter().filter(|c| c.is_opened()).count();
+
+                if n > 0 {
+                    warn!(
+                        "{:?}: {} open children remain(s), closing...",
+                        self_ref, n
+                    );
 
-                for child in self_ref.children.iter() {
-                    if child.is_opened() {
-                        child.close().await.ok();
+                    for child in self_ref.children.iter() {
+                        if child.is_opened() {
+                            child.close().await.ok();
+                        }
                     }
                 }
-            }
 
-            self_ref.children.clear();
-        });
+                self_ref.children.clear();
+            });
+        }
 
         self.as_mut().unregister_io_device();
         unsafe {

io-engine/src/core/reactor.rs

@@ -362,8 +362,15 @@ impl Reactor {
         task
     }
 
-    /// spawn a future locally on the current core block until the future is
+    /// Spawns a future locally on the current core block until the future is
     /// completed. The master core is used.
+    /// # Warning
+    /// This code should only be used for testing and not running production!
+    /// This is because when calling block_on from a thread_poll callback, we
+    /// may be leaving messages behind, which can lead to timeouts etc...
+    /// A work-around to make this safe could be to potentially "pull" the
+    /// messages which haven't been polled, and poll them here before
+    /// proceeding to re-poll via thread_poll again.
     pub fn block_on<F, R>(future: F) -> Option<R>
     where
         F: Future<Output = R> + 'static,

io-engine/src/grpc/mod.rs

@@ -2,7 +2,6 @@ use futures::channel::oneshot::Receiver;
 use nix::errno::Errno;
 pub use server::MayastorGrpcServer;
 use std::{
-    error::Error,
     fmt::{Debug, Display},
     future::Future,
     time::Duration,
@@ -158,22 +157,6 @@ macro_rules! spdk_submit {
 
 pub type GrpcResult<T> = std::result::Result<Response<T>, Status>;
 
-/// call the given future within the context of the reactor on the first core
-/// on the init thread, while the future is waiting to be completed the reactor
-/// is continuously polled so that forward progress can be made
-pub fn rpc_call<G, I, L, A>(future: G) -> Result<Response<A>, tonic::Status>
-where
-    G: Future<Output = Result<I, L>> + 'static,
-    I: 'static,
-    L: Into<Status> + Error + 'static,
-    A: 'static + From<I>,
-{
-    Reactor::block_on(future)
-        .unwrap()
-        .map(|r| Response::new(A::from(r)))
-        .map_err(|e| e.into())
-}
-
 /// Submit rpc code to the primary reactor.
 pub fn rpc_submit<F, R, E>(
     future: F,