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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| use crate::{ | ||
| sync::{self, RwLock}, | ||
| task::{Task, TaskCtxt}, | ||
| unrecoverable, | ||
| }; | ||
| use alloc::sync::Arc; | ||
| use core::{ | ||
| arch::asm, | ||
| sync::atomic::{AtomicPtr, Ordering}, | ||
| }; | ||
|
|
||
| /// The `Arc` of the currently running task. After the scheduler is started, | ||
| /// it should always be `Some`. When no other user task is ready, the current | ||
| /// task should be the idle task. | ||
| /// | ||
| /// The [`RwLock`] around it is only for sanity check. | ||
| /// | ||
| /// NOTE: We must use a [`RwLock`] instead of a | ||
| /// [`SpinSchedSafe`](crate::sync::SpinSchedSafe) to protect the data. This is | ||
| /// because the [`more_stack`](crate::task::more_stack) and | ||
| /// [`less_stack`](crate::task::less_stack) function need to access the current | ||
| /// task struct. However, `more_stack` or `less_stack` may be invoked when the | ||
| /// current task struct is being accessed. Thus, using a spin lock will cause | ||
| /// deadlock, and `RwLock` is necessary. | ||
| static CUR_TASK: RwLock<Option<Arc<Task>>> = RwLock::new(None); | ||
|
|
||
| /// Set another task to be the current task. The current task will lock its | ||
| /// context field. See [`Task`] for the context lock invariant. | ||
| pub(super) fn update_cur_task(task: Arc<Task>) { | ||
| let mut write_guard = CUR_TASK.write(); | ||
|
|
||
| // Unlock the context struct for the task being context switched out of | ||
| // the CPU. The only case where the current task is `None` is upon system | ||
| // boot. | ||
| // | ||
| // Safety: The lock was acquired by the next statement when the task was | ||
| // being context switched on to the CPU. | ||
| if let Some(ref cur_task) = *write_guard { | ||
| unsafe { | ||
| cur_task.force_unlock_ctxt(); | ||
| } | ||
| } | ||
|
|
||
| // Acquire the context lock for the task going to be executed on the CPU. | ||
| let task_ctxt_ptr = task.lock_ctxt(); | ||
|
|
||
| // Update the global pointer so that the context switch assembly sequence | ||
| // will find the new task context through the pointer. | ||
| CUR_TASK_CTXT_PTR.store(task_ctxt_ptr, Ordering::SeqCst); | ||
|
|
||
| // Update the global `Arc` current task reference. | ||
| write_guard.replace(task); | ||
| } | ||
|
|
||
| /// Point to the struct that preserves the task's callee-saved registers upon | ||
| /// context switch. This pointer is used by the context switch assembly | ||
| /// sequence in [`context_switch`](crate::interrupt::context_switch). | ||
| #[no_mangle] | ||
| pub(crate) static CUR_TASK_CTXT_PTR: AtomicPtr<TaskCtxt> = AtomicPtr::new(core::ptr::null_mut()); | ||
|
|
||
| /// Do things with the current task struct. When the given closure is being | ||
| /// executed, the current task `Arc` will be locked in reader mode and no | ||
| /// context switch will happen during this period. | ||
| /// | ||
| /// [`with_current_task_arc`] has slightly better performance than this | ||
| /// function. Use that function if `&Task` suffices. | ||
| pub(crate) fn with_current_task_arc<F, R>(closure: F) -> R | ||
| 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 read_guard = CUR_TASK.read(); | ||
|
|
||
| // Run the closure. | ||
| if let Some(cur_task) = &*read_guard { | ||
| closure(cur_task.clone()) | ||
| } else { | ||
| unrecoverable::die(); | ||
| } | ||
| } | ||
|
|
||
| /// Do things with the current task struct. When the given closure is being | ||
| /// executed, the current task `Arc` will be locked in reader mode and no | ||
| /// context switch will happen during this period. | ||
| /// | ||
| /// This function has slightly better performance than [`with_current_task_arc`]. | ||
| pub(crate) fn with_current_task<F, R>(closure: F) -> R | ||
| 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 read_guard = CUR_TASK.read(); | ||
|
|
||
| // Run the closure. | ||
| if let Some(cur_task) = &*read_guard { | ||
| closure(cur_task) | ||
| } else { | ||
| unrecoverable::die(); | ||
| } | ||
| } | ||
|
|
||
| /// Return if the code is currently executing in an interrupt service routine | ||
| /// (ISR) context. | ||
| pub(crate) fn is_in_isr_context() -> bool { | ||
| let ipsr: u32; | ||
|
|
||
| unsafe { | ||
| asm!( | ||
| "mrs {}, ipsr", | ||
| out(reg) ipsr, | ||
| options(nomem, nostack) | ||
| ); | ||
| } | ||
|
|
||
| ipsr != 0 | ||
| } | ||
|
|
||
| /// Return if the code is currently executing in the PendSV exception context. | ||
| pub(crate) fn is_in_pendsv_context() -> bool { | ||
| let ipsr: u32; | ||
|
|
||
| unsafe { | ||
| asm!( | ||
| "mrs {}, ipsr", | ||
| out(reg) ipsr, | ||
| options(nomem, nostack) | ||
| ); | ||
| } | ||
|
|
||
| ipsr == 14 | ||
| } |
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