fabaccess-bffh/runtime/executor/src/pool.rs

//!
//! Pool of threads to run lightweight processes
//!
//! We spawn futures onto the pool with [`spawn`] method of global run queue or
//! with corresponding [`Worker`]'s spawn method.
//!
//! [`spawn`]: crate::pool::spawn
//! [`Worker`]: crate::run_queue::Worker

use std::cell::Cell;
use crate::thread_manager::{ThreadManager, DynamicRunner};
use lightproc::lightproc::LightProc;
use lightproc::recoverable_handle::RecoverableHandle;
use std::future::Future;
use std::iter::Iterator;
use std::marker::PhantomData;
use std::mem::MaybeUninit;
use std::sync::Arc;
use std::time::Duration;
use crossbeam_deque::{Injector, Stealer};
use crate::run::block;
use crate::worker::{Sleeper, WorkerThread};

#[derive(Debug)]
struct Spooler<'a> {
    pub spool: Arc<Injector<LightProc>>,
    threads: &'a ThreadManager<AsyncRunner>,
    _marker: PhantomData<&'a ()>,
}

impl Spooler<'_> {
    pub fn new() -> Self {
        let spool = Arc::new(Injector::new());
        let threads = Box::leak(Box::new(
            ThreadManager::new(2, AsyncRunner, spool.clone())));
        threads.initialize();
        Self { spool, threads, _marker: PhantomData }
    }
}

#[derive(Clone, Debug)]
/// Global executor
pub struct Executor<'a> {
    spooler: Arc<Spooler<'a>>,
}

impl<'a, 'executor: 'a> Executor<'executor> {
    pub fn new() -> Self {
        Executor {
            spooler: Arc::new(Spooler::new()),
        }
    }

    fn schedule(&self) -> impl Fn(LightProc) + 'a {
        let task_queue = self.spooler.spool.clone();
        move |lightproc: LightProc| {
            task_queue.push(lightproc)
        }
    }

    ///
    /// Spawn a process (which contains future + process stack) onto the executor from the global level.
    ///
    /// # Example
    /// ```rust
    /// use executor::prelude::*;
    ///
    /// # #[cfg(feature = "tokio-runtime")]
    /// # #[tokio::main]
    /// # async fn main() {
    /// #    start();
    /// # }
    /// #
    /// # #[cfg(not(feature = "tokio-runtime"))]
    /// # fn main() {
    /// #    start();
    /// # }
    /// #
    /// # fn start() {
    ///
    /// let executor = Spooler::new();
    ///
    /// let handle = executor.spawn(
    ///     async {
    ///         panic!("test");
    ///     },
    /// );
    ///
    /// executor.run(
    ///     async {
    ///         handle.await;
    ///     }
    /// );
    /// # }
    /// ```
    pub fn spawn<F, R>(&self, future: F) -> RecoverableHandle<R>
        where
            F: Future<Output = R> + Send + 'a,
            R: Send + 'a,
    {
        let (task, handle) =
            LightProc::recoverable(future, self.schedule());
        task.schedule();
        handle
    }

    pub fn spawn_local<F, R>(&self, future: F) -> RecoverableHandle<R>
        where
            F: Future<Output = R> + 'a,
            R: Send + 'a,
    {
        let (task, handle) =
            LightProc::recoverable(future, schedule_local());
        task.schedule();
        handle
    }

    /// Block the calling thread until the given future completes.
    ///
    /// # Example
    /// ```rust
    /// use executor::prelude::*;
    /// use lightproc::prelude::*;
    ///
    /// let executor = Spooler::new();
    ///
    /// let mut sum = 0;
    ///
    /// executor.run(
    ///     async {
    ///         (0..10_000_000).for_each(|_| {
    ///             sum += 1;
    ///         });
    ///     }
    /// );
    /// ```
    pub fn run<F, R>(&self, future: F) -> R
        where
            F: Future<Output = R>,
    {
        unsafe {
            // An explicitly uninitialized `R`. Until `assume_init` is called this will not call any
            // drop code for R
            let mut out = MaybeUninit::uninit();

            // Wrap the future into one that stores the result into `out`.
            let future = {
                let out: *mut R = out.as_mut_ptr();
                async move {
                    out.write(future.await);
                }
            };

            // Pin the future onto the stack.
            pin_utils::pin_mut!(future);

            // Block on the future and and wait for it to complete.
            block(future);

            // Assume that if the future completed and didn't panic it fully initialized its output
            out.assume_init()
        }
    }
}

#[derive(Debug)]
struct AsyncRunner;

impl DynamicRunner for AsyncRunner {
    fn setup(task_queue: Arc<Injector<LightProc>>) -> Sleeper<LightProc> {
        let (worker, sleeper) = WorkerThread::new(task_queue);
        install_worker(worker);

        sleeper
    }

    fn run_static<'b>(fences: impl Iterator<Item=&'b Stealer<LightProc>>, park_timeout: Duration) -> ! {
        let worker = get_worker();
        worker.run_timeout(fences, park_timeout)
    }

    fn run_dynamic<'b>(fences: impl Iterator<Item=&'b Stealer<LightProc>>) -> ! {
        let worker = get_worker();
        worker.run(fences)
    }

    fn run_standalone<'b>(fences: impl Iterator<Item=&'b Stealer<LightProc>>) {
        let worker = get_worker();
        worker.run_once(fences)
    }
}

thread_local! {
    static WORKER: Cell<Option<WorkerThread<'static, LightProc>>> = Cell::new(None);
}

fn get_worker() -> &'static WorkerThread<'static, LightProc> {
    WORKER.with(|cell| {
        let worker = unsafe {
            &*cell.as_ptr() as &'static Option<WorkerThread<_>>
        };
        worker.as_ref()
            .expect("AsyncRunner running outside Executor context")
    })
}

fn install_worker(worker_thread: WorkerThread<'static, LightProc>) {
    WORKER.with(|cell| {
        cell.replace(Some(worker_thread));
    });
}

fn schedule_local() -> impl Fn(LightProc) {
    let worker = get_worker();
    let unparker = worker.unparker().clone();
    move |lightproc| {
        // This is safe because we never replace the value in that Cell and thus never drop the
        // SharedWorker pointed to.
        worker.schedule_local(lightproc);
        // We have to unpark the worker thread for our task to be run.
        unparker.unpark();
    }
}