From a7ed040799f5d2c2a2a7021fef840a6717d88d44 Mon Sep 17 00:00:00 2001
From: Jorge Aparicio <jorge.aparicio@ferrous-systems.com>
Date: Thu, 22 Jul 2021 09:27:42 +0200
Subject: [PATCH] migration/0.5: cover #[lock_free]

I think this completes #488
---
 book/en/src/migration/migration_v5.md | 43 +++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/book/en/src/migration/migration_v5.md b/book/en/src/migration/migration_v5.md
index 210063bf5e..24353d2a31 100644
--- a/book/en/src/migration/migration_v5.md
+++ b/book/en/src/migration/migration_v5.md
@@ -201,6 +201,49 @@ fn bar(cx: bar::Context) {
 
 Note that the performance does not change thanks to LLVM's optimizations which optimizes away unnecessary locks.
 
+## Lock-free resource access
+
+In RTIC 0.5 resources shared by tasks running at the same priority could be accessed *without* the `lock` API.
+This is still possible in 0.6: the `#[shared]` resource must be annotated with the field-level `#[lock_free]` attribute.
+
+v0.5 code:
+
+``` rust
+struct Resources {
+    counter: u64,
+}
+
+#[task(resources = [counter])]
+fn a(cx: a::Context) {
+    *cx.resources.counter += 1;
+}
+
+#[task(resources = [counter])]
+fn b(cx: b::Context) {
+    *cx.resources.counter += 1;
+}
+```
+
+v0.6 code:
+
+``` rust
+#[shared]
+struct Shared {
+    #[lock_free]
+    counter: u64,
+}
+
+#[task(shared = [counter])]
+fn a(cx: a::Context) {
+    *cx.shared.counter += 1;
+}
+
+#[task(shared = [counter])]
+fn b(cx: b::Context) {
+    *cx.shared.counter += 1;
+}
+```
+
 ## no `static mut` transform
 
 `static mut` variables are no longer transformed to safe `&'static mut` references.