From 6bf1c76d842b40cd1b24b4a517e42e624ade836f Mon Sep 17 00:00:00 2001 From: Jorge Aparicio Date: Wed, 21 Jul 2021 15:46:09 +0200 Subject: [PATCH] book/resources: do not use the lock API in the very first example instead stick to `#[local]` resources --- book/en/src/by-example/resources.md | 29 ++++++++------ examples/resource.rs | 61 +++++++++++++++++------------ 2 files changed, 53 insertions(+), 37 deletions(-) diff --git a/book/en/src/by-example/resources.md b/book/en/src/by-example/resources.md index 3a3e0b7660..b0e7590445 100644 --- a/book/en/src/by-example/resources.md +++ b/book/en/src/by-example/resources.md @@ -7,9 +7,11 @@ Resources are data visible only to functions declared within the `#[app]` module. The framework gives the user complete control over which context can access which resource. -All resources are declared as a single `struct` within the `#[app]` -module. Each field in the structure corresponds to a different resource. -The `struct` must be annotated with the following attribute: `#[resources]`. +All resources are declared as *two* `struct`s within the `#[app]` module. +Each field in these structures corresponds to a different resource. +One `struct` must be annotated with the attribute `#[local]`. +The other `struct` must be annotated with the attribute `#[shared]`. +The difference between these two sets of resources will be covered later. Resources can optionally be given an initial value using the `#[init]` attribute. Resources that are not given an initial value are referred to as @@ -17,12 +19,13 @@ attribute. Resources that are not given an initial value are referred to as page. Each context (task handler, `init` or `idle`) must declare the resources it -intends to access in its corresponding metadata attribute using the `resources` -argument. This argument takes a list of resource names as its value. The listed -resources are made available to the context under the `resources` field of the -`Context` structure. +intends to access in its corresponding metadata attribute using either the +`local` or `shared` argument. This argument takes a list of resource names as +its value. The listed resources are made available to the context under the +`local` and `shared` fields of the `Context` structure. -The example application shown below contains two interrupt handlers that share access to a resource named `shared`. +The example application shown below contains two interrupt handlers. +Each handler has access to its own `#[local]` resource. ``` rust {{#include ../../../../examples/resource.rs}} @@ -33,13 +36,14 @@ $ cargo run --example resource {{#include ../../../../ci/expected/resource.run}} ``` -Note that the `shared` resource cannot be accessed from `idle`. Attempting to do so results in a compile error. +A `#[local]` resource cannot be accessed from outside the task it was associated to in a `#[task]` attribute. +Assigning the same `#[local]` resource to more than one task is a compile-time error. ## `lock` -Critical sections are required to access shared mutable data in a data race-free manner. +Critical sections are required to access `#[shared]` resources in a data race-free manner. -The `resources` field of the passed `Context` implements the [`Mutex`] trait for each shared resource accessible to the task. +The `shared` field of the passed `Context` implements the [`Mutex`] trait for each shared resource accessible to the task. The only method on this trait, [`lock`], runs its closure argument in a critical section. @@ -91,7 +95,7 @@ $ cargo run --example late {{#include ../../../../ci/expected/late.run}} ``` -## Only shared access +## Only shared (`&-`) access By default the framework assumes that all tasks require exclusive access (`&mut-`) to resources but it is possible to specify that a task only requires shared access (`&-`) to a resource using the `&resource_name` syntax in the `resources` list. @@ -121,4 +125,3 @@ There exists two other options dealing with resources this is safe. * `#[task_local]`: there must be only one task using this resource, similar to a `static mut` task local resource, but (optionally) set-up by init. - diff --git a/examples/resource.rs b/examples/resource.rs index 2c7dffe334..260f67535b 100644 --- a/examples/resource.rs +++ b/examples/resource.rs @@ -13,55 +13,68 @@ mod app { use lm3s6965::Interrupt; #[shared] - struct Shared { - shared: u32, - } + struct Shared {} #[local] - struct Local {} + struct Local { + local_to_uart0: i64, + local_to_uart1: i64, + } #[init] fn init(_: init::Context) -> (Shared, Local, init::Monotonics) { rtic::pend(Interrupt::UART0); rtic::pend(Interrupt::UART1); - (Shared { shared: 0 }, Local {}, init::Monotonics()) + ( + Shared {}, + Local { + local_to_uart0: 0, + local_to_uart1: 0, + }, + init::Monotonics(), + ) } - // `shared` cannot be accessed from this context + // `#[local]` resources cannot be accessed from this context #[idle] fn idle(_cx: idle::Context) -> ! { debug::exit(debug::EXIT_SUCCESS); - // error: no `shared` field in `idle::Context` - // _cx.shared.shared += 1; + // error: no `local` field in `idle::Context` + // _cx.local.local_to_uart0 += 1; + + // error: no `local` field in `idle::Context` + // _cx.local.local_to_uart1 += 1; loop { cortex_m::asm::nop(); } } - // `shared` can be accessed from this context + // `local_to_uart0` can only be accessed from this context // defaults to priority 1 - #[task(binds = UART0, shared = [shared])] - fn uart0(mut cx: uart0::Context) { - let shared = cx.shared.shared.lock(|shared| { - *shared += 1; - *shared - }); + #[task(binds = UART0, local = [local_to_uart0])] + fn uart0(cx: uart0::Context) { + *cx.local.local_to_uart0 += 1; + let local_to_uart0 = cx.local.local_to_uart0; - hprintln!("UART0: shared = {}", shared).unwrap(); + // error: no `local_to_uart1` field in `uart0::LocalResources` + cx.local.local_to_uart1 += 1; + + hprintln!("UART0: local_to_uart0 = {}", local_to_uart0).unwrap(); } - // `shared` can be accessed from this context + // `shared` can only be accessed from this context // explicitly set to priority 2 - #[task(binds = UART1, shared = [shared], priority = 2)] - fn uart1(mut cx: uart1::Context) { - let shared = cx.shared.shared.lock(|shared| { - *shared += 1; - *shared - }); + #[task(binds = UART1, local = [local_to_uart1], priority = 2)] + fn uart1(cx: uart1::Context) { + *cx.local.local_to_uart1 += 1; + let local_to_uart1 = cx.local.local_to_uart1; - hprintln!("UART1: shared = {}", shared).unwrap(); + // error: no `local_to_uart0` field in `uart1::LocalResources` + // cx.local.local_to_uart0 += 1; + + hprintln!("UART1: local_to_uart1 = {}", local_to_uart1).unwrap(); } }