burritos/src/kernel/synch.rs

use crate::utility::list::List;
use crate::kernel::thread::Thread;
use crate::simulator::interrupt::InterruptStatus::InterruptOff;
use crate::simulator::machine::Machine;
use std::cell::RefCell;
use std::rc::Rc;


use super::scheduler::Scheduler;
use super::system::System;
use super::thread_manager::ThreadManager;

///     Structure of a Semaphore used for synchronisation
pub struct Semaphore {

    /// Counter of simultanous Semaphore
    counter:i32,
    /// QUeue of Semaphore waiting to be exucated
    waiting_queue:List<Rc<RefCell<Thread>>>,

}

impl Semaphore {

    ///     Initializes a semaphore, so that it can be used for synchronization.
    ///
    ///  ### Parameters
    /// - *counter* initial value of counter
    /// - *thread_manager* Thread manager which managing threads
    pub fn new(counter: i32) -> Semaphore{
        Semaphore { counter, waiting_queue: List::new()}
    }

    ///     Decrement the value, and wait if it becomes < 0. Checking the
    ///	value and decrementing must be done atomically, so we
    ///	need to disable interrupts before checking the value.
    ///
    ///	Note that thread_manager::thread_sleep assumes that interrupts are disabled
    ///	when it is called.
    ///
    /// ### Parameters TODO Refaire
    /// - *current_thread* the current thread
    /// - *machine* the machine where the threads are executed
    pub fn p(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);
        self.counter -= 1;
        if self.counter < 0 {
            match system.get_thread_manager().get_g_current_thread() {
                Some(thread) => {
                    self.waiting_queue.push(Rc::clone(thread));
                    system.get_thread_manager().thread_sleep(system, Rc::clone(thread));
                },
                None => unreachable!("Current thread should not be None")
            }
        }
        system.get_machine().interrupt.set_status(old_status);
    }

    /// Increment semaphore value, waking up a waiting thread if any.
    /// As with P(), this operation must be atomic, so we need to disable
    /// interrupts.
    ///
    /// scheduler::ready_to_run() assumes that interrupts
    /// are disabled when it is called.
    ///
    /// ### Parameters
    /// - **machine** the machine where the threads are executed
    /// - **scheduler** the scheduler which determine which thread to execute
    pub fn v(&mut self, system: &mut System){
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);
        self.counter += 1;
        if self.waiting_queue.peek() != None {
            system.get_thread_manager().g_scheduler.ready_to_run(self.waiting_queue.pop().unwrap());
        }
        system.get_machine().interrupt.set_status(old_status);
    }
}

/// Lock used for synchronisation, can be interpreted has a Semaphore with a
/// counter of 1
/// It's used for critical parts
pub struct Lock{

    /// Thread owning the lock
    owner: Option<Rc<RefCell<Thread>>>,
    /// The queue of threads waiting for execution
    waiting_queue:List<Rc<RefCell<Thread>>>,
    /// A boolean definig if the lock is free or not
    free: bool

}

impl Lock {

    ///    Initialize a Lock, so that it can be used for synchronization.
    /// The lock is initialy free
    ///
    /// ### Parameters
    /// - **thread_manager** Thread manager which managing threads
    pub fn new() -> Lock {
        Lock { owner: None, waiting_queue: List::new(), free: true }
    }

    ///    Wait until the lock become free.  Checking the
    ///	state of the lock (free or busy) and modify it must be done
    ///	atomically, so we need to disable interrupts before checking
    ///	the value of free.
    ///
    ///	Note that thread_manager::thread_seep assumes that interrupts are disabled
    ///	when it is called.
    ///
    /// ### Parameters
    /// - **current_thread** the current thread
    /// - **machine** the machine where the threads are executed
    pub fn acquire(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);

        if self.free {
            self.free = false;
            self.owner = Option::Some(match system.get_thread_manager().get_g_current_thread() {
                Some(th) => {
                    Rc::clone(th)
                },
                None => unreachable!()
            });
        } else {
            let t = system.get_thread_manager().get_g_current_thread();
            match t {
                Some(x) => {
                    let x = Rc::clone(x);
                    self.waiting_queue.push(Rc::clone(&x));
                    system.thread_sleep(Rc::clone(&x));
                },
                None => unreachable!("Current thread should not be None")
            }
        }

        system.get_machine().interrupt.set_status(old_status);
    }

    ///     Wake up a waiter if necessary, or release it if no thread is waiting.
    /// We check that the lock is held by the g_current_thread.
    ///	As with Acquire, this operation must be atomic, so we need to disable
    ///	interrupts.  scheduler::ready_to_run() assumes that threads
    ///	are disabled when it is called.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    pub fn release(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);
        
        match system.get_thread_manager().get_g_current_thread() {
            Some(thread) => {
                if self.held_by_current_thread(system) {
                    if self.waiting_queue.peek() != None {
                        self.owner = Some(self.waiting_queue.pop().unwrap());
                        match &self.owner {
                            Some(x) => system.get_thread_manager().g_scheduler.ready_to_run(Rc::clone(&x)),
                            None => ()
                        }
                    } else {
                        self.free = true;
                        self.owner = None;
                    }
                }
            }
            None => ()
        }

        system.get_machine().interrupt.set_status(old_status);
    }

    pub fn held_by_current_thread(&mut self, system: &mut System) -> bool {
        match &self.owner {
            Some(x) => 
                match system.get_thread_manager().get_g_current_thread() {
                    Some(thread) => Rc::ptr_eq(&x, thread),
                    None => false
                }
            None => false
        }
    }
}

/// Structure of a condition used for synchronisation
pub struct Condition{

    /// The queue of threads waiting for execution
    waiting_queue:List<Rc<RefCell<Thread>>>,
    
}

impl Condition {

    /// Initializes a Condition, so that it can be used for synchronization.
    ///
    /// ### Parameters
    /// - *thread_manager* Thread manager which managing threads
    pub fn new() -> Condition {
        Condition{ waiting_queue: List::new()}
    }

    ///  Block the calling thread (put it in the wait queue).
    ///  This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **current_thread** the current thread
    /// - **machine** the machine where threads are executed
    pub fn wait(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);

        match system.get_thread_manager().get_g_current_thread() {
            Some(thread) => {
                self.waiting_queue.push(Rc::clone(thread));
                system.thread_sleep(Rc::clone(thread));
            },
            None => unreachable!()
        }

        system.get_machine().interrupt.set_status(old_status);
    }

    /// Wake up the first thread of the wait queue (if any).
    /// This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    pub fn signal(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);

        if self.waiting_queue.peek() != None {
            system.get_thread_manager().g_scheduler.ready_to_run(self.waiting_queue.pop().unwrap());
        }

        system.get_machine().interrupt.set_status(old_status);

    }

    /// Wake up all threads waiting in the waitqueue of the condition
    /// This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    pub fn broadcast(&mut self, system: &mut System) {
        let old_status = system.get_machine().interrupt.set_status(InterruptOff);

        while self.waiting_queue.peek() != None {
            system.get_thread_manager().g_scheduler.ready_to_run(self.waiting_queue.pop().unwrap());
        }
        system.get_machine().interrupt.set_status(old_status);

    }

}

#[cfg(test)]
mod test {
    use std::{rc::Rc, cell::RefCell};

    use crate::{kernel::{thread::Thread, synch::{Semaphore, Lock}}, init_system, simulator::machine::Machine};

    #[test]
    fn test_semaphore_single() {
        // Init
        let system = init_system!();
        let mut semaphore = Semaphore::new(1, Rc::clone(&system.borrow_mut().get_thread_manager()));
        let thread = Rc::new(RefCell::new(Thread::new("test_semaphore")));
        // P
        semaphore.p(thread, Rc::clone(&system));
        assert_eq!(semaphore.counter, 0);
        assert!(semaphore.waiting_queue.is_empty());
        // V
        semaphore.v(Rc::clone(&system));
        assert_eq!(semaphore.counter, 1);
        assert!(semaphore.waiting_queue.is_empty());
    }

    #[test]
    #[ignore]
    fn test_semaphore_multiple() {
        // Init
        let system = init_system!();
        let tm = system.borrow_mut().get_thread_manager();
        let mut semaphore = Semaphore::new(2, Rc::clone(&tm));
        let thread1 = Rc::new(RefCell::new(Thread::new("test_semaphore_1")));
        let thread2 = Rc::new(RefCell::new(Thread::new("test_semaphore_2")));
        let thread3 = Rc::new(RefCell::new(Thread::new("test_semaphore_3")));

        let mut borrow_tm = tm.borrow_mut();
        let scheduler = &mut borrow_tm.g_scheduler;
        scheduler.ready_to_run(Rc::clone(&thread1));
        scheduler.ready_to_run(Rc::clone(&thread2));
        scheduler.ready_to_run(Rc::clone(&thread3));
        // P
        borrow_tm.set_g_current_thread(Some(Rc::clone(&thread1)));
        semaphore.p(thread1, Rc::clone(&system));
        assert_eq!(semaphore.counter, 1);
        assert!(semaphore.waiting_queue.is_empty());
        
        borrow_tm.set_g_current_thread(Some(Rc::clone(&thread2)));
        semaphore.p(thread2, Rc::clone(&system));
        assert_eq!(semaphore.counter, 0);
        assert!(semaphore.waiting_queue.is_empty());

        borrow_tm.set_g_current_thread(Some(Rc::clone(&thread3)));
        semaphore.p(thread3, Rc::clone(&system));
        assert_eq!(semaphore.counter, -1);
        assert!(semaphore.waiting_queue.iter().count() == 1);

        // V
        semaphore.v(Rc::clone(&system));
        assert_eq!(semaphore.counter, 0);
        assert!(semaphore.waiting_queue.is_empty());

        semaphore.v(Rc::clone(&system));
        assert_eq!(semaphore.counter, 1);
        assert!(semaphore.waiting_queue.is_empty());

        semaphore.v(Rc::clone(&system));
        assert_eq!(semaphore.counter, 2);
        assert!(semaphore.waiting_queue.is_empty());
    }



    #[test]
    #[ignore]
    fn test_lock_simple() {
        let system = init_system!();
        let sys = system.borrow_mut();
        let tm = sys.get_thread_manager();
        let thread = Rc::new(RefCell::new(Thread::new("test_lock")));
        tm.borrow_mut().set_g_current_thread(Some(Rc::clone(&thread)));
        let mut lock = Lock::new(Rc::clone(&tm));

        assert!(lock.free);
        lock.acquire(Some(Rc::clone(&thread)), Rc::clone(&system));
        assert!(lock.held_by_current_thread(Rc::clone(&thread)));

        assert!(!lock.free);
        lock.release(Rc::clone(&system), Rc::clone(&thread));
        assert!(!lock.held_by_current_thread(thread));
        assert!(lock.free);
    }

    #[test]
    #[ignore]
    fn test_lock_multiple() {
        let system = init_system!();
        let thread1 = Rc::new(RefCell::new(Thread::new("test_lock1")));
        let thread2 = Rc::new(RefCell::new(Thread::new("test_lock2")));
        let thread3 = Rc::new(RefCell::new(Thread::new("test_lock3")));

        let tm = system.borrow_mut().get_thread_manager();
        tm.borrow_mut().set_g_current_thread(Some(Rc::clone(&thread1)));
        let mut lock = Lock::new(Rc::clone(&tm));

        assert!(lock.free);
        lock.acquire(Some(Rc::clone(&thread1)), Rc::clone(&system));
        assert!(lock.held_by_current_thread(Rc::clone(&thread1)));
        assert!(!lock.free);

        tm.borrow_mut().set_g_current_thread(Some(Rc::clone(&thread2)));
        lock.acquire(Some(Rc::clone(&thread2)), Rc::clone(&system));
        tm.borrow_mut().set_g_current_thread(Some(Rc::clone(&thread1)));

        
        assert!(lock.held_by_current_thread(Rc::clone(&thread1)));
        assert!(lock.waiting_queue.iter().count() == 1);
        assert!(!lock.free);

        lock.release(Rc::clone(&system), Rc::clone(&thread1));
        assert!(!lock.held_by_current_thread(thread1));
        assert!(lock.held_by_current_thread(Rc::clone(&thread2)));
        assert!(!lock.free);

        tm.borrow_mut().set_g_current_thread(Some(Rc::clone(&thread2)));


        lock.release(Rc::clone(&system), Rc::clone(&thread2));
        assert!(!lock.held_by_current_thread(thread2));
        assert!(lock.free);
    }
}