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// License: see LICENSE file at root directory of `master` branch

//! # Job

/// # A job to be used by [`Blackhole`][crate:Blackhole]
///
/// ## Usage
///
/// You can return new job from [`::run()`][::run()] for it to be run.
///
/// [crate:Blackhole]: struct.Blackhole.html
/// [::run()]: trait.Job.html#tymethod.run
pub trait Job: Send + 'static {

    /// # Runs the job
    fn run(&mut self) -> Option<Box<Job>>;

}

/// # Runs a job to the end
pub fn run_to_end<J>(mut job: J) where J: Job {
    if let Some(mut job) = job.run() {
        loop {
            match job.run() {
                Some(new_job) => job = new_job,
                None => break,
            };
        }
    }
}

/// # A job that runs once
///
/// ## Panics
///
/// It will panic if run more than once.
#[derive(Debug)]
pub struct OneTime<F> where F: FnOnce() + Send + 'static {

    /// # The job
    f: Option<F>,

}

impl<F> OneTime<F> where F: FnOnce() + Send + 'static {

    /// # Makes new instance
    pub fn new(f: F) -> Self {
        Self {
            f: Some(f),
        }
    }

}

impl<F> Job for OneTime<F> where F: FnOnce() + Send + 'static {

    fn run(&mut self) -> Option<Box<Job>> {
        self.f.take().expect("OneTime job must be run at most once")();
        None
    }

}

#[test]
fn test_one_time() {
    use std::sync::{
        Arc,
        atomic::{self, ATOMIC_BOOL_INIT},
    };

    const ORDERING: atomic::Ordering = atomic::Ordering::Relaxed;

    let data = Arc::new(ATOMIC_BOOL_INIT);
    assert!(data.load(ORDERING) == false);

    run_to_end({
        let data = data.clone();
        OneTime::new(move || data.store(true, ORDERING))
    });
    assert!(data.load(ORDERING));
}