Add the concept of local tasks with an example

Add test for spawning a local task from a different prio

This ensures that there is no method on the spawning
task's local spawner for spawning the local task
with the other priority.

Add test for spawning a local task from init

This ensures that there is no method in the globaly
available module with the same name as the local task.

Add passing test for local task with non Send/Sync arg

Ensure it is possible to pass a non send and non Sync
argument when spawning a local task. This is ok
since it will only be possible to spawn the task
on the same executor and priority level

Fix spawn-local-no-send-sync

Rename `is_local_task` to just `local_task` and allow omitting the value

Move example and remove success test

Update tests for - Rename `is_local_task` to just `local_task` and allow omitting the value

Move tests to rtic/ui

Revert fmt

Add exit to example

Fix example

Fix example

Update changelog

Author: usbalbin

ci/expected/lm3s6965/spawn_local.run

@@ -0,0 +1,2 @@
+Hello from task1!
+Hello from task2!

examples/lm3s6965/examples/spawn_local.rs

@@ -0,0 +1,38 @@
+#![no_main]
+#![no_std]
+
+use panic_semihosting as _;
+
+#[rtic::app(device = lm3s6965, dispatchers = [SSI0])]
+mod app {
+    use cortex_m_semihosting::{debug, hprintln};
+    use super::*;
+
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(_cx: init::Context) -> (Shared, Local) {
+        task1::spawn().unwrap();
+        //task2::spawn(Default::default()).ok(); <--- This is rejected since it is a local task
+        (Shared {}, Local {})
+    }
+
+    #[task(priority = 1)]
+    async fn task1(cx: task1::Context) {
+        hprintln!("Hello from task1!");
+        cx.local_spawner.task2(Default::default()).unwrap();
+    }
+
+    #[task(priority = 1, local_task = true)]
+    async fn task2(_cx: task2::Context, _nsns: NotSendNotSync) {
+        hprintln!("Hello from task2!");
+        debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
+    }
+}
+
+#[derive(Default, Debug)]
+struct NotSendNotSync(core::marker::PhantomData<*mut u8>);

rtic-macros/CHANGELOG.md

@@ -14,6 +14,7 @@ For each category, *Added*, *Changed*, *Fixed* add new entries at the top!
 ### Added
 
 - Outer attributes applied to RTIC app module are now forwarded to the generated code.
+- Add attribute `local_task` for tasks that may take args that are !Send/!Sync and can only be spawned from same executor
 
 ## [v2.2.0] - 2025-06-22
 

rtic-macros/src/codegen/module.rs

@@ -1,5 +1,6 @@
 use crate::syntax::{ast::App, Context};
 use crate::{analyze::Analysis, codegen::bindings::interrupt_mod, codegen::util};
+
 use proc_macro2::TokenStream as TokenStream2;
 use quote::quote;
 
@@ -112,37 +113,7 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
     let internal_context_name = util::internal_task_ident(name, "Context");
     let exec_name = util::internal_task_ident(name, "EXEC");
 
-    items.push(quote!(
-        #(#cfgs)*
-        /// Execution context
-        #[allow(non_snake_case)]
-        #[allow(non_camel_case_types)]
-        pub struct #internal_context_name<'a> {
-            #[doc(hidden)]
-            __rtic_internal_p: ::core::marker::PhantomData<&'a ()>,
-            #(#fields,)*
-        }
-
-        #(#cfgs)*
-        impl<'a> #internal_context_name<'a> {
-            #[inline(always)]
-            #[allow(missing_docs)]
-            pub unsafe fn new(#core) -> Self {
-                #internal_context_name {
-                    __rtic_internal_p: ::core::marker::PhantomData,
-                    #(#values,)*
-                }
-            }
-        }
-    ));
-
-    module_items.push(quote!(
-        #(#cfgs)*
-        #[doc(inline)]
-        pub use super::#internal_context_name as Context;
-    ));
-
-    if let Context::SoftwareTask(..) = ctxt {
+    if let Context::SoftwareTask(t) = ctxt {
         let spawnee = &app.software_tasks[name];
         let priority = spawnee.args.priority;
         let cfgs = &spawnee.cfgs;
@@ -163,13 +134,21 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
         let (input_args, input_tupled, input_untupled, input_ty) =
             util::regroup_inputs(&spawnee.inputs);
 
+        let local_task = app.software_tasks[t].args.local_task;
+        let unsafety = if local_task {
+            // local tasks are only safe to call from the same executor
+            quote! { unsafe }
+        } else {
+            quote! {}
+        };
+
         // Spawn caller
         items.push(quote!(
             #(#cfgs)*
             /// Spawns the task directly
             #[allow(non_snake_case)]
             #[doc(hidden)]
-            pub fn #internal_spawn_ident(#(#input_args,)*) -> ::core::result::Result<(), #input_ty> {
+            pub #unsafety fn #internal_spawn_ident(#(#input_args,)*) -> ::core::result::Result<(), #input_ty> {
                 // SAFETY: If `try_allocate` succeeds one must call `spawn`, which we do.
                 unsafe {
                     let exec = rtic::export::executor::AsyncTaskExecutor::#from_ptr_n_args(#name, &#exec_name);
@@ -204,11 +183,70 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
             }
         ));
 
-        module_items.push(quote!(
-            #(#cfgs)*
-            #[doc(inline)]
-            pub use super::#internal_spawn_ident as spawn;
-        ));
+        if !local_task {
+            module_items.push(quote!(
+                #(#cfgs)*
+                #[doc(inline)]
+                pub use super::#internal_spawn_ident as spawn;
+            ));
+        }
+
+        let local_tasks_on_same_executor: Vec<_> = app
+            .software_tasks
+            .iter()
+            .filter(|(_, t)| t.args.local_task && t.args.priority == priority)
+            .collect();
+
+        if !local_tasks_on_same_executor.is_empty() {
+            let local_spawner = util::internal_task_ident(t, "LocalSpawner");
+            fields.push(quote! {
+                /// Used to spawn tasks on the same executor
+                ///
+                /// This is useful for tasks that take args which are !Send/!Sync.
+                ///
+                /// NOTE: This only works with tasks marked `local_task = true`
+                /// and which have the same priority and thus will run on the
+                /// same executor.
+                pub local_spawner: #local_spawner
+            });
+            let tasks = local_tasks_on_same_executor
+                .iter()
+                .map(|(ident, task)| {
+                    // Copied mostly from software_tasks.rs
+                    let internal_spawn_ident = util::internal_task_ident(ident, "spawn");
+                    let attrs = &task.attrs;
+                    let cfgs = &task.cfgs;
+                    let inputs = &task.inputs;
+                    let generics = if task.is_bottom {
+                        quote!()
+                    } else {
+                        quote!(<'a>)
+                    };
+                    let input_vals = inputs.iter().map(|i| &i.pat).collect::<Vec<_>>();
+                    let (_input_args, _input_tupled, _input_untupled, input_ty) = util::regroup_inputs(&task.inputs);
+                    quote! {
+                        #(#attrs)*
+                        #(#cfgs)*
+                        #[allow(non_snake_case)]
+                        pub(super) fn #ident #generics(&self #(,#inputs)*) -> ::core::result::Result<(), #input_ty> {
+                            // SAFETY: This is safe to call since this can only be called
+                            // from the same executor
+                            unsafe { #internal_spawn_ident(#(#input_vals,)*) }
+                        }
+                    }
+                })
+                .collect::<Vec<_>>();
+            values.push(quote!(local_spawner: #local_spawner { _p: core::marker::PhantomData }));
+            items.push(quote! {
+                struct #local_spawner {
+                    _p: core::marker::PhantomData<*mut ()>,
+                }
+
+                impl #local_spawner {
+                    #(#tasks)*
+                }
+            });
+        }
 
         module_items.push(quote!(
             #(#cfgs)*
@@ -217,6 +255,36 @@ pub fn codegen(ctxt: Context, app: &App, analysis: &Analysis) -> TokenStream2 {
         ));
     }
 
+    items.push(quote!(
+        #(#cfgs)*
+        /// Execution context
+        #[allow(non_snake_case)]
+        #[allow(non_camel_case_types)]
+        pub struct #internal_context_name<'a> {
+            #[doc(hidden)]
+            __rtic_internal_p: ::core::marker::PhantomData<&'a ()>,
+            #(#fields,)*
+        }
+
+        #(#cfgs)*
+        impl<'a> #internal_context_name<'a> {
+            #[inline(always)]
+            #[allow(missing_docs)]
+            pub unsafe fn new(#core) -> Self {
+                #internal_context_name {
+                    __rtic_internal_p: ::core::marker::PhantomData,
+                    #(#values,)*
+                }
+            }
+        }
+    ));
+
+    module_items.push(quote!(
+        #(#cfgs)*
+        #[doc(inline)]
+        pub use super::#internal_context_name as Context;
+    ));
+
     if items.is_empty() {
         quote!()
     } else {

rtic-macros/src/syntax/analyze.rs

@@ -285,13 +285,16 @@ pub(crate) fn app(app: &App) -> Result<Analysis, syn::Error> {
     for (name, spawnee) in &app.software_tasks {
         let spawnee_prio = spawnee.args.priority;
 
+        // TODO: What is this?
         let channel = channels.entry(spawnee_prio).or_default();
         channel.tasks.insert(name.clone());
 
-        // All inputs are send as we do not know from where they may be spawned.
-        spawnee.inputs.iter().for_each(|input| {
-            send_types.insert(input.ty.clone());
-        });
+        if !spawnee.args.local_task {
+            // All inputs are send as we do not know from where they may be spawned.
+            spawnee.inputs.iter().for_each(|input| {
+                send_types.insert(input.ty.clone());
+            });
+        }
     }
 
     // No channel should ever be empty

rtic-macros/src/syntax/ast.rs

@@ -256,6 +256,12 @@ pub struct SoftwareTaskArgs {
 
     /// Shared resources that can be accessed from this context
     pub shared_resources: SharedResources,
+
+    /// Local tasks
+    /// 
+    /// Local tasks can only be spawned from the same executor.
+    /// However they do not require Send and Sync
+    pub local_task: bool,
 }
 
 impl Default for SoftwareTaskArgs {
@@ -264,6 +270,7 @@ impl Default for SoftwareTaskArgs {
             priority: 0,
             local_resources: LocalResources::new(),
             shared_resources: SharedResources::new(),
+            local_task: false,
         }
     }
 }

rtic-macros/src/syntax/parse.rs

@@ -11,7 +11,7 @@ use syn::{
     braced,
     parse::{self, Parse, ParseStream, Parser},
     token::Brace,
-    Attribute, Ident, Item, LitInt, Meta, Token,
+    Attribute, Ident, Item, LitBool, LitInt, Meta, Token,
 };
 
 use crate::syntax::{
@@ -197,6 +197,7 @@ fn task_args(tokens: TokenStream2) -> parse::Result<Either<HardwareTaskArgs, Sof
         let mut shared_resources = None;
         let mut local_resources = None;
         let mut prio_span = None;
+        let mut local_task = None;
 
         loop {
             if input.is_empty() {
@@ -208,7 +209,27 @@ fn task_args(tokens: TokenStream2) -> parse::Result<Either<HardwareTaskArgs, Sof
             let ident_s = ident.to_string();
 
             // Handle equal sign
-            let _: Token![=] = input.parse()?;
+            let eq = input.parse::<Token![=]>();
+
+            // Only local_task supports omitting the value
+            if &*ident_s == "local_task" {
+                if local_task.is_some() {
+                    return Err(parse::Error::new(
+                        ident.span(),
+                        "argument appears more than once",
+                    ));
+                }
+
+                if eq.is_ok() {
+                    let lit: LitBool = input.parse()?;
+                    local_task = Some(lit.value);
+                } else {
+                    local_task = Some(true); // Default to true
+                }
+                break;
+            } else if let Err(e) = eq {
+                return Err(e);
+            };
 
             match &*ident_s {
                 "binds" => {
@@ -291,6 +312,7 @@ fn task_args(tokens: TokenStream2) -> parse::Result<Either<HardwareTaskArgs, Sof
         }
         let shared_resources = shared_resources.unwrap_or_default();
         let local_resources = local_resources.unwrap_or_default();
+        let local_task = local_task.unwrap_or(false);
 
         Ok(if let Some(binds) = binds {
             // Hardware tasks can't run at anything lower than 1
@@ -317,6 +339,7 @@ fn task_args(tokens: TokenStream2) -> parse::Result<Either<HardwareTaskArgs, Sof
                 priority,
                 shared_resources,
                 local_resources,
+                local_task,
             })
         })
     })

rtic/CHANGELOG.md

@@ -23,6 +23,7 @@ Example:
 ### Added
 
 - Outer attributes applied to RTIC app module are now forwarded to the generated code.
+- Add attribute `local_task` for tasks that may take args that are !Send/!Sync and can only be spawned from same executor
 
 ### Changed
 

rtic/ui/spawn-local-different-exec.rs

@@ -0,0 +1,23 @@
+#![no_main]
+
+#[rtic::app(device = lm3s6965, dispatchers = [SSI0, GPIOA])]
+mod app {
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(_cx: init::Context) -> (Shared, Local) {
+        (Shared {}, Local {})
+    }
+
+    #[task(priority = 1, local_task)]
+    async fn foo(_cx: foo::Context) {}
+
+    #[task(priority = 2)]
+    async fn bar(cx: bar::Context) {
+        cx.local_spawner.foo().ok();
+    }
+}

rtic/ui/spawn-local-different-exec.stderr

@@ -0,0 +1,7 @@
+error[E0609]: no field `local_spawner` on type `__rtic_internal_bar_Context<'_>`
+  --> ui/spawn-local-different-exec.rs:21:12
+   |
+21 |         cx.local_spawner.foo().ok();
+   |            ^^^^^^^^^^^^^ unknown field
+   |
+   = note: available field is: `__rtic_internal_p`