Struct Waker 

pub struct Waker {
    wait_queue: Mutex<VecDeque<usize>>,
    block_type: BlockedType,
    name: &'static str,
}

A synchronization primitive that manages waiting and waking of tasks

The Waker struct provides a mechanism for tasks to wait for specific events and be woken up when those events occur. It maintains a queue of waiting task IDs and provides methods to block the current task or wake up waiting tasks.

Examples

// Create a new interruptible waker for UART receive events
static UART_RX_WAKER: Waker = Waker::new_interruptible("uart_rx");

// In a blocking read function
UART_RX_WAKER.wait();

// In an interrupt handler
UART_RX_WAKER.wake_one();

Fields

wait_queue: Mutex<VecDeque<usize>>

Queue of waiting task IDs

block_type: BlockedType

The type of blocking this waker uses (interruptible or uninterruptible)

name: &'static str

Human-readable name for debugging purposes

Implementations

impl Waker

pub const fn new_interruptible(name: &'static str) -> Self

Create a new interruptible waker

Interruptible wakers allow waiting tasks to be interrupted by signals or other asynchronous events. This is suitable for user I/O operations where cancellation might be needed.

Arguments

• name - A human-readable name for debugging purposes

Examples

static KEYBOARD_WAKER: Waker = Waker::new_interruptible("keyboard");

pub const fn new_uninterruptible(name: &'static str) -> Self

Create a new uninterruptible waker

Uninterruptible wakers ensure that waiting tasks cannot be interrupted and will wait until the event occurs. This is suitable for critical operations like disk I/O where data integrity is important.

Arguments

• name - A human-readable name for debugging purposes

Examples

static DISK_IO_WAKER: Waker = Waker::new_uninterruptible("disk_io");

pub fn wait(&self, task_id: usize, trapframe: &mut Trapframe)

Block the current task and add it to the wait queue

This method puts the current task into a blocked state and adds its ID to the wait queue. The task will remain blocked until another part of the system calls wake_one() or wake_all() on this waker.

Behavior

1. Gets the current task ID
2. Sets the task state to Blocked(self.block_type) FIRST
3. Adds the task ID to the wait queue
4. Calls the scheduler to yield CPU to other tasks
5. Returns when the task is woken up and rescheduled

Note

This function returns when the task is woken up by another part of the system. The calling code can then continue execution, typically to re-check the condition that caused the wait.

Critical Section

To prevent race conditions between wait() and wake_one()/wake_all():

1. Set task state to Blocked BEFORE adding to queue
2. This ensures wake_task() can safely operate even if called immediately

pub fn wait_with_timeout( &self, task_id: usize, trapframe: &mut Trapframe, timeout_ticks: Option<u64>, ) -> bool

Block the task until woken or the timeout elapses.

Returns true if woken by event, false if timeout elapsed.

pub fn wake_one(&self) -> bool

Wake up one waiting task

This method removes one task from the wait queue and moves it from the blocked queue to the ready queue, making it eligible for scheduling again.

Returns

• true if a task was woken up
• false if the wait queue was empty

Examples

// In an interrupt handler
if UART_RX_WAKER.wake_one() {
    // A task was woken up
}

pub fn wake_all(&self) -> usize

Wake up all waiting tasks

This method removes all tasks from the wait queue and moves them from the blocked queue to the ready queue, making them all eligible for scheduling again.

Returns

The number of tasks that were woken up

Examples

// Wake all tasks waiting for a broadcast event
let woken_count = BROADCAST_WAKER.wake_all();
println!("Woke up {} tasks", woken_count);

pub fn block_type(&self) -> BlockedType

Get the blocking type of this waker

Returns

The BlockedType (either Interruptible or Uninterruptible)

pub fn waiting_count(&self) -> usize

Get the number of tasks currently waiting

Returns

The number of tasks in the wait queue

pub fn name(&self) -> &'static str

Get the name of this waker

Returns

The human-readable name for debugging purposes

pub fn get_waiting_task_ids(&self) -> VecDeque<usize>

Get a list of task IDs currently waiting in the queue

This method returns a snapshot of all task IDs currently waiting in this waker’s queue. Useful for debugging and monitoring.

Returns

A vector containing all waiting task IDs

Examples

let waiting_tasks = waker.get_waiting_task_ids();
println!("Tasks waiting: {:?}", waiting_tasks);

pub fn is_task_waiting(&self, task_id: usize) -> bool

Check if a specific task is waiting in this waker

Arguments

• task_id - The ID of the task to check

Returns

true if the task is waiting in this waker, false otherwise

pub fn get_stats(&self) -> WakerStats

Get detailed statistics about this waker

This method provides detailed information about the current state of the waker, including all waiting tasks and their metadata.

Returns

A WakerStats struct containing comprehensive state information

Examples

let stats = uart_waker.get_stats();
// Use Debug trait to print the stats

pub fn is_empty(&self) -> bool

Print debug information about this waker

Outputs detailed information about the waker’s current state including name, blocking type, waiting task count, and task IDs. Useful for debugging and monitoring system state.

Examples

waker.debug_print();
// Output:
// [Waker DEBUG] uart_rx: Interruptible, 3 waiting tasks: [42, 137, 89]

Check if the waker has any waiting tasks

Returns

true if there are no waiting tasks, false otherwise

pub fn clear_queue(&self) -> usize

Clear all waiting tasks without waking them

This is a dangerous operation that should only be used in exceptional circumstances like system cleanup or error recovery. The tasks will remain in blocked state and need to be handled separately.

Returns

The number of tasks that were removed from the queue

Safety

This operation can leave tasks in a permanently blocked state. Use with extreme caution.

Trait Implementations

impl Debug for Waker

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.