Refactor scheduler suspension.

src/allocator/mod.rs

@@ -6,7 +6,7 @@ use core::{
 
 use super::{
     interrupt::{svc, trap_frame::TrapFrame},
-    schedule::scheduler,
+    schedule::scheduler::Scheduler,
     task,
     unrecoverable::{self, Lethal},
 };
@@ -165,7 +165,7 @@ pub(crate) fn initialize() {
 fn die_if_not_in_svc() {
     // Only perform sanity check after the scheduler has started, otherwise
     // we may still be running with the bootstrap stack with MSP.
-    if !scheduler::has_started() {
+    if !Scheduler::has_started() {
         return;
     }
 
@@ -187,7 +187,7 @@ fn die_if_not_in_svc() {
 fn die_if_not_in_svc_or_pendsv() {
     // Only perform sanity check after the scheduler has started, otherwise
     // we may still be running with the bootstrap stack with MSP.
-    if !scheduler::has_started() {
+    if !Scheduler::has_started() {
         return;
     }
 

src/boot/system_init.rs

@@ -1,7 +1,7 @@
 //! The module performs the initialization before running the user defined main
 //! function.
 
-use crate::{allocator, config, schedule::scheduler, task, unrecoverable::Lethal};
+use crate::{allocator, config, schedule::scheduler::Scheduler, task, unrecoverable::Lethal};
 use alloc::boxed::Box;
 use core::sync::atomic::AtomicPtr;
 use cortex_m::peripheral::scb::SystemHandler;
@@ -37,7 +37,7 @@ pub(super) extern "C" fn system_start() -> ! {
     // the idle task context and then perform a context switch to run the main
     // task.
     unsafe {
-        scheduler::start();
+        Scheduler::start();
     }
 }
 

src/interrupt/context_switch.rs

@@ -1,6 +1,6 @@
 use crate::{
     config,
-    schedule::{current, scheduler},
+    schedule::{current, scheduler::Scheduler},
     unrecoverable,
 };
 use core::arch::asm;
@@ -110,5 +110,5 @@ extern "C" fn pendsv_handler(ex_ret_lr: u32) {
 
     // The `CUR_TASK_CTXT_PTR` pointer will be updated to reflect the next
     // chosen task to run.
-    scheduler::pick_next();
+    Scheduler::pick_next();
 }

src/interrupt/svc_handler.rs

@@ -16,7 +16,7 @@
 use super::trap_frame::TrapFrame;
 use crate::{
     allocator, config,
-    schedule::scheduler,
+    schedule::scheduler::Scheduler,
     task::{self, MoreStackReason, TaskLocalStorage},
     unrecoverable::{self, Lethal},
 };
@@ -29,6 +29,9 @@ pub(crate) enum SVCNum {
     /// The calling task wants to get off from CPU. A task may voluntarily
     /// yield the CPU or it may be forced to yield when becoming blocked on a
     /// synchronization primitive.
+    ///
+    /// Note that the SVC handler does not directly perform a context switch.
+    /// Instead, a PendSV will be tail chained to perform it.
     TaskYield = 1,
     /// The task wants to terminate and release its task struct.
     TaskDestroy = 2,
@@ -144,10 +147,8 @@ fn get_svc_num(tf: &TrapFrame) -> SVCNum {
 /// the assembly code.
 extern "C" fn svc_handler(tf: &mut TrapFrame, ctxt: &mut TaskSVCCtxt) {
     match get_svc_num(tf) {
-        // Task wants to yield. Mark its state as ready so that the
-        // scheduler can schedule it later.
-        SVCNum::TaskYield => scheduler::yield_cur_task_from_isr(),
-        SVCNum::TaskDestroy => scheduler::destroy_current_task_and_schedule(),
+        SVCNum::TaskYield => Scheduler::yield_current_task_from_svc(),
+        SVCNum::TaskDestroy => Scheduler::drop_current_task_from_svc(),
         SVCNum::TaskLessStack => task::less_stack(tf, ctxt),
         SVCNum::TaskMoreStack => task::more_stack(tf, ctxt, MoreStackReason::Normal),
         SVCNum::TaskMoreStackFromDrop => task::more_stack(tf, ctxt, MoreStackReason::Drop),

src/schedule/current.rs

@@ -1,5 +1,6 @@
+use super::scheduler::Scheduler;
 use crate::{
-    sync::{self, RwLock},
+    sync::RwLock,
     task::{Task, TaskCtxt},
     unrecoverable,
 };
@@ -69,7 +70,7 @@ where
     F: FnOnce(Arc<Task>) -> R,
 {
     // Suspend the scheduler and lock the current task `Arc` in reader mode.
-    let _sched_suspend_guard = sync::suspend_scheduler();
+    let _sched_suspend_guard = Scheduler::suspend();
     let read_guard = CUR_TASK.read();
 
     // Run the closure.
@@ -90,7 +91,7 @@ where
     F: FnOnce(&Task) -> R,
 {
     // Suspend the scheduler and lock the current task `Arc` in reader mode.
-    let _sched_suspend_guard = sync::suspend_scheduler();
+    let _sched_suspend_guard = Scheduler::suspend();
     let read_guard = CUR_TASK.read();
 
     // Run the closure.
@@ -102,7 +103,7 @@ where
 }
 
 /// Return if the code is currently executing in an interrupt service routine
-/// (ISR) context.
+/// (ISR), in contrast to in a task.
 pub(crate) fn is_in_isr_context() -> bool {
     let ipsr: u32;
 
@@ -117,6 +118,12 @@ pub(crate) fn is_in_isr_context() -> bool {
     ipsr != 0
 }
 
+/// Return if the code is currently executing in a task, in contrast to in an
+/// interrupt service routine (ISR).
+pub(crate) fn is_in_task_context() -> bool {
+    !is_in_isr_context()
+}
+
 /// Return if the code is currently executing in the PendSV exception context.
 pub(crate) fn is_in_pendsv_context() -> bool {
     let ipsr: u32;