Ensure that a waitable is only added to one wait set at a time

Author: nnmm

rclrs/src/error.rs

@@ -27,6 +27,8 @@ pub enum RclrsError {
         /// The error indicating the position of the nul byte.
         err: NulError,
     },
+    /// It was attempted to add a waitable to a wait set twice.
+    AlreadyAddedToWaitSet,
 }
 
 impl Display for RclrsError {
@@ -37,6 +39,12 @@ impl Display for RclrsError {
             RclrsError::StringContainsNul { s, .. } => {
                 write!(f, "Could not convert string '{}' to CString", s)
             }
+            RclrsError::AlreadyAddedToWaitSet => {
+                write!(
+                    f,
+                    "Could not add entity to wait set because it was already added to a wait set"
+                )
+            }
         }
     }
 }
@@ -68,6 +76,7 @@ impl Error for RclrsError {
             RclrsError::RclError { msg, .. } => msg.as_ref().map(|e| e as &dyn Error),
             RclrsError::UnknownRclError { msg, .. } => msg.as_ref().map(|e| e as &dyn Error),
             RclrsError::StringContainsNul { err, .. } => Some(err).map(|e| e as &dyn Error),
+            RclrsError::AlreadyAddedToWaitSet => None,
         }
     }
 }

rclrs/src/node/client.rs

@@ -1,8 +1,8 @@
-use crate::node::client::oneshot::Canceled;
 use futures::channel::oneshot;
 use std::boxed::Box;
 use std::collections::HashMap;
 use std::ffi::CString;
+use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
 
 use crate::error::{RclReturnCode, ToResult};
@@ -21,6 +21,7 @@ unsafe impl Send for rcl_client_t {}
 pub struct ClientHandle {
     rcl_client_mtx: Mutex<rcl_client_t>,
     rcl_node_mtx: Arc<Mutex<rcl_node_t>>,
+    pub(crate) in_use_by_wait_set: Arc<AtomicBool>,
 }
 
 impl ClientHandle {
@@ -40,15 +41,6 @@ impl Drop for ClientHandle {
     }
 }
 
-impl From<Canceled> for RclrsError {
-    fn from(_: Canceled) -> Self {
-        RclrsError::RclError {
-            code: RclReturnCode::Error,
-            msg: None,
-        }
-    }
-}
-
 /// Trait to be implemented by concrete Client structs.
 ///
 /// See [`Client<T>`] for an example.
@@ -113,6 +105,7 @@ where
         let handle = Arc::new(ClientHandle {
             rcl_client_mtx: Mutex::new(rcl_client),
             rcl_node_mtx: node.rcl_node_mtx.clone(),
+            in_use_by_wait_set: Arc::new(AtomicBool::new(false)),
         });
 
         Ok(Self {

rclrs/src/node/service.rs

@@ -1,5 +1,6 @@
 use std::boxed::Box;
 use std::ffi::CString;
+use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
 
 use crate::error::{RclReturnCode, ToResult};
@@ -20,6 +21,7 @@ unsafe impl Send for rcl_service_t {}
 pub struct ServiceHandle {
     handle: Mutex<rcl_service_t>,
     node_handle: Arc<Mutex<rcl_node_t>>,
+    pub(crate) in_use_by_wait_set: Arc<AtomicBool>,
 }
 
 impl ServiceHandle {
@@ -103,6 +105,7 @@ where
         let handle = Arc::new(ServiceHandle {
             handle: Mutex::new(service_handle),
             node_handle: node.rcl_node_mtx.clone(),
+            in_use_by_wait_set: Arc::new(AtomicBool::new(false)),
         });
 
         Ok(Self {

rclrs/src/node/subscription.rs

@@ -7,6 +7,7 @@ use std::boxed::Box;
 use std::ffi::CStr;
 use std::ffi::CString;
 use std::marker::PhantomData;
+use std::sync::atomic::AtomicBool;
 use std::sync::Arc;
 
 use rosidl_runtime_rs::{Message, RmwMessage};
@@ -21,6 +22,7 @@ unsafe impl Send for rcl_subscription_t {}
 pub struct SubscriptionHandle {
     rcl_subscription_mtx: Mutex<rcl_subscription_t>,
     rcl_node_mtx: Arc<Mutex<rcl_node_t>>,
+    pub(crate) in_use_by_wait_set: Arc<AtomicBool>,
 }
 
 impl SubscriptionHandle {
@@ -116,6 +118,7 @@ where
         let handle = Arc::new(SubscriptionHandle {
             rcl_subscription_mtx: Mutex::new(rcl_subscription),
             rcl_node_mtx: node.rcl_node_mtx.clone(),
+            in_use_by_wait_set: Arc::new(AtomicBool::new(false)),
         });
 
         Ok(Self {

rclrs/src/wait.rs

@@ -25,6 +25,9 @@ use std::vec::Vec;
 
 use parking_lot::Mutex;
 
+mod exclusivity_guard;
+use exclusivity_guard::*;
+
 /// A struct for waiting on subscriptions and other waitable entities to become ready.
 pub struct WaitSet {
     rcl_wait_set: rcl_wait_set_t,
@@ -33,9 +36,9 @@ pub struct WaitSet {
     // The subscriptions that are currently registered in the wait set.
     // This correspondence is an invariant that must be maintained by all functions,
     // even in the error case.
-    subscriptions: Vec<Arc<dyn SubscriptionBase>>,
-    clients: Vec<Arc<dyn ClientBase>>,
-    services: Vec<Arc<dyn ServiceBase>>,
+    subscriptions: Vec<ExclusivityGuard<Arc<dyn SubscriptionBase>>>,
+    clients: Vec<ExclusivityGuard<Arc<dyn ClientBase>>>,
+    services: Vec<ExclusivityGuard<Arc<dyn ServiceBase>>>,
 }
 
 /// A list of entities that are ready, returned by [`WaitSet::wait`].
@@ -118,17 +121,22 @@ impl WaitSet {
 
     /// Adds a subscription to the wait set.
     ///
-    /// It is possible, but not useful, to add the same subscription twice.
-    ///
-    /// This will return an error if the number of subscriptions in the wait set is larger than the
-    /// capacity set in [`WaitSet::new`].
+    /// # Errors
+    /// - If the subscription was already added to this wait set or another one,
+    ///   [`AlreadyAddedToWaitSet`][1] will be returned
+    /// - If the number of subscriptions in the wait set is larger than the
+    ///   capacity set in [`WaitSet::new`], [`WaitSetFull`][2] will be returned
     ///
-    /// The same subscription must not be added to multiple wait sets, because that would make it
-    /// unsafe to simultaneously wait on those wait sets.
+    /// [1]: crate::RclrsError
+    /// [2]: crate::RclReturnCode
     pub fn add_subscription(
         &mut self,
         subscription: Arc<dyn SubscriptionBase>,
     ) -> Result<(), RclrsError> {
+        let exclusive_subscription = ExclusivityGuard::new(
+            Arc::clone(&subscription),
+            Arc::clone(&subscription.handle().in_use_by_wait_set),
+        )?;
         unsafe {
             // SAFETY: I'm not sure if it's required, but the subscription pointer will remain valid
             // for as long as the wait set exists, because it's stored in self.subscriptions.
@@ -140,20 +148,25 @@ impl WaitSet {
             )
         }
         .ok()?;
-        self.subscriptions.push(subscription);
+        self.subscriptions.push(exclusive_subscription);
         Ok(())
     }
 
     /// Adds a client to the wait set.
     ///
-    /// It is possible, but not useful, to add the same client twice.
-    ///
-    /// This will return an error if the number of clients in the wait set is larger than the
-    /// capacity set in [`WaitSet::new`].
+    /// # Errors
+    /// - If the client was already added to this wait set or another one,
+    ///   [`AlreadyAddedToWaitSet`][1] will be returned
+    /// - If the number of clients in the wait set is larger than the
+    ///   capacity set in [`WaitSet::new`], [`WaitSetFull`][2] will be returned
     ///
-    /// The same client must not be added to multiple wait sets, because that would make it
-    /// unsafe to simultaneously wait on those wait sets.
+    /// [1]: crate::RclrsError
+    /// [2]: crate::RclReturnCode
     pub fn add_client(&mut self, client: Arc<dyn ClientBase>) -> Result<(), RclrsError> {
+        let exclusive_client = ExclusivityGuard::new(
+            Arc::clone(&client),
+            Arc::clone(&client.handle().in_use_by_wait_set),
+        )?;
         unsafe {
             // SAFETY: I'm not sure if it's required, but the client pointer will remain valid
             // for as long as the wait set exists, because it's stored in self.clients.
@@ -165,20 +178,25 @@ impl WaitSet {
             )
         }
         .ok()?;
-        self.clients.push(client);
+        self.clients.push(exclusive_client);
         Ok(())
     }
 
     /// Adds a service to the wait set.
     ///
-    /// It is possible, but not useful, to add the same service twice.
-    ///
-    /// This will return an error if the number of services in the wait set is larger than the
-    /// capacity set in [`WaitSet::new`].
+    /// # Errors
+    /// - If the service was already added to this wait set or another one,
+    ///   [`AlreadyAddedToWaitSet`][1] will be returned
+    /// - If the number of services in the wait set is larger than the
+    ///   capacity set in [`WaitSet::new`], [`WaitSetFull`][2] will be returned
     ///
-    /// The same service must not be added to multiple wait sets, because that would make it
-    /// unsafe to simultaneously wait on those wait sets.
+    /// [1]: crate::RclrsError
+    /// [2]: crate::RclReturnCode
     pub fn add_service(&mut self, service: Arc<dyn ServiceBase>) -> Result<(), RclrsError> {
+        let exclusive_service = ExclusivityGuard::new(
+            Arc::clone(&service),
+            Arc::clone(&service.handle().in_use_by_wait_set),
+        )?;
         unsafe {
             // SAFETY: I'm not sure if it's required, but the service pointer will remain valid
             // for as long as the wait set exists, because it's stored in self.services.
@@ -190,7 +208,7 @@ impl WaitSet {
             )
         }
         .ok()?;
-        self.services.push(service);
+        self.services.push(exclusive_service);
         Ok(())
     }
 
@@ -245,7 +263,9 @@ impl WaitSet {
             // https://github.com/ros2/rcl/blob/35a31b00a12f259d492bf53c0701003bd7f1745c/rcl/include/rcl/wait.h#L419
             let wait_set_entry = unsafe { *self.rcl_wait_set.subscriptions.add(i) };
             if !wait_set_entry.is_null() {
-                ready_entities.subscriptions.push(subscription.clone());
+                ready_entities
+                    .subscriptions
+                    .push(Arc::clone(&subscription.waitable));
             }
         }
         for (i, client) in self.clients.iter().enumerate() {
@@ -254,7 +274,7 @@ impl WaitSet {
             // https://github.com/ros2/rcl/blob/35a31b00a12f259d492bf53c0701003bd7f1745c/rcl/include/rcl/wait.h#L419
             let wait_set_entry = unsafe { *self.rcl_wait_set.clients.add(i) };
             if !wait_set_entry.is_null() {
-                ready_entities.clients.push(client.clone());
+                ready_entities.clients.push(Arc::clone(&client.waitable));
             }
         }
         for (i, service) in self.services.iter().enumerate() {
@@ -263,7 +283,7 @@ impl WaitSet {
             // https://github.com/ros2/rcl/blob/35a31b00a12f259d492bf53c0701003bd7f1745c/rcl/include/rcl/wait.h#L419
             let wait_set_entry = unsafe { *self.rcl_wait_set.services.add(i) };
             if !wait_set_entry.is_null() {
-                ready_entities.services.push(service.clone());
+                ready_entities.services.push(Arc::clone(&service.waitable));
             }
         }
         Ok(ready_entities)

rclrs/src/wait/exclusivity_guard.rs

@@ -0,0 +1,36 @@
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+use crate::RclrsError;
+
+/// A helper struct for tracking whether the waitable is currently in a wait set.
+///
+/// When this struct is constructed, which happens when adding an entity to the wait set,
+/// it checks that the atomic boolean is false and sets it to true.
+/// When it is dropped, which happens when it is removed from the wait set,
+/// or the wait set itself is dropped, it sets the atomic bool to false.
+pub(super) struct ExclusivityGuard<T> {
+    in_use_by_wait_set: Arc<AtomicBool>,
+    pub(super) waitable: T,
+}
+
+impl<T> Drop for ExclusivityGuard<T> {
+    fn drop(&mut self) {
+        self.in_use_by_wait_set.store(false, Ordering::Relaxed)
+    }
+}
+
+impl<T> ExclusivityGuard<T> {
+    pub fn new(waitable: T, in_use_by_wait_set: Arc<AtomicBool>) -> Result<Self, RclrsError> {
+        if in_use_by_wait_set
+            .compare_exchange(false, true, Ordering::Relaxed, Ordering::Relaxed)
+            .is_err()
+        {
+            return Err(RclrsError::AlreadyAddedToWaitSet);
+        }
+        Ok(Self {
+            in_use_by_wait_set,
+            waitable,
+        })
+    }
+}