Struct Data

struct Data {
    tasks: DenseSlotMap<Ti, Task>,
    awake: VecDeque<Ti>,
    progressing_until_stalled: Option<ProgressingUntilStalled>,
    scheduling: SchedulingPolicy,
    thread_to_run: ThreadDescriptor,
}

Executor’s state

Task state machine

A task is created in tasks, Awake, so also in awake.

When we poll it, we take it out of awake and set it to Asleep, and then call poll(). Any time after that, it can be made Awake again (and put back onto awake) by the waker (ActualWaker, wrapped in Waker).

The task’s future is of course also present here in this data structure. However, during poll we must release the lock, so we cannot borrow the future from Data. Instead, we move it out. So Task.fut is an Option.

“Main” task - the argument to block_on

The signature of BlockOn::block_on accepts a non-'static future (and a non-Send/Sync one).

So we cannot store that future in Data because Data is 'static. Instead, this main task future is passed as an argument down the call stack. In the data structure we simply store a placeholder, TaskFutureInfo::Main.

Fields

tasks: DenseSlotMap<Ti, Task>

Tasks

Includes tasks spawned with spawn, and also the future passed to block_on.

awake: VecDeque<Ti>

awake lists precisely: tasks that are Awake, plus maybe stale TaskIds

Tasks are pushed onto the back when woken, so back is the most recently woken.

progressing_until_stalled: Option<ProgressingUntilStalled>

If a future from progress_until_stalled exists

scheduling: SchedulingPolicy

Scheduling policy

thread_to_run: ThreadDescriptor

(Sub)thread we want to run now

At any one time only one thread is meant to be running. Other threads are blocked in condvar wait, waiting for this to change.

Modified only within thread_context_switch_send_instruction_to_run, which takes responsibility for preserving the following invariants:

1. no-one but the named thread is allowed to modify this field.
2. after modifying this field, signal thread_condvar

Implementations

impl Data

fn insert_task(&mut self, desc: String, fut: TaskFutureInfo) -> TaskId

Insert a task given its TaskFutureInfo and return its TaskId.

impl Data

fn schedule(&mut self) -> Option<TaskId>

Return the next task to run

The task is removed from awake, but state is not set to Asleep. The caller must restore the invariant!

impl Data

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

Dump tasks and their sleep location backtraces

impl Data

fn debug_dump(&mut self)

Convenience function: dump including backtraces, to stderr

Trait Implementations

impl Debug for Data

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

Formats the value using the given formatter.

impl Default for Data

fn default() -> Self

Returns the “default value” for a type.

impl From<Data> for MockExecutor

fn from(data: Data) -> MockExecutor

Converts to this type from the input type.