Merge pull request #169 from japaric/late-must-be-send

book: note that late resources must be Send

book/en/src/by-example/types-send-sync.md

@@ -39,6 +39,19 @@ The example below shows where a type that doesn't implement `Send` can be used.
 {{#include ../../../../examples/not-send.rs}}
 ```
 
+It's important to note that late initialization of resources is effectively a
+send operation where the initial value is sent from `idle`, which has the lowest
+priority of `0`, to a task with will run with a priority greater than or equal
+to `1`. Thus all late resources need to implement the `Send` trait.
+
+Sharing a resource with `init` can be used to implement late initialization, see
+example below. For that reason, resources shared with `init` must also implement
+the `Send` trait.
+
+``` rust
+{{#include ../../../../examples/shared-with-init.rs}}
+```
+
 ## `Sync`
 
 Similarly, [`Sync`] is a marker trait for "types for which it is safe to share

ci/script.sh

@@ -109,6 +109,7 @@ main() {
                 types
                 not-send
                 not-sync
+                shared-with-init
 
                 generics
                 ramfunc

examples/shared-with-init.rs

@@ -0,0 +1,38 @@
+//! `examples/shared-with-init.rs`
+
+#![deny(unsafe_code)]
+#![deny(warnings)]
+#![no_main]
+#![no_std]
+
+extern crate panic_halt;
+
+use cortex_m_semihosting::debug;
+use lm3s6965::Interrupt;
+use rtfm::app;
+
+pub struct MustBeSend;
+
+#[app(device = lm3s6965)]
+const APP: () = {
+    static mut SHARED: Option<MustBeSend> = None;
+
+    #[init(resources = [SHARED])]
+    fn init() {
+        // this `message` will be sent to task `UART0`
+        let message = MustBeSend;
+        *resources.SHARED = Some(message);
+
+        rtfm::pend(Interrupt::UART0);
+    }
+
+    #[interrupt(resources = [SHARED])]
+    fn UART0() {
+        if let Some(message) = resources.SHARED.take() {
+            // `message` has been received
+            drop(message);
+
+            debug::exit(debug::EXIT_SUCCESS);
+        }
+    }
+};