check(&array, INIT_SIZE);

    }

    #[test]

    fn decrease_size() {

        const INIT_SIZE: usize = 16;

        const FINAL_SIZE: usize = 8;

        let mut array = RawArray::new();

        array.resize(INIT_SIZE);

        fill(&mut array, INIT_SIZE);

        array.resize(FINAL_SIZE);

        check(&array, FINAL_SIZE);

    }

    #[test]

    fn increase_and_decrease_size() {

        let sizes = [12, 8, 6, 150, 128, 32, 16, 90, 4, 18, 27];

        let min_size = *sizes.iter().min().unwrap();

        let max_size = *sizes.iter().max().unwrap();

        let mut array = RawArray::new();

        array.resize(max_size);

        fill(&mut array, max_size);

            array.resize(size);

            assert_eq!(array.cap(), size);

        }

        check(&array, min_size);

    }

}

use std::sync::atomic::{AtomicU32, Ordering};

use crate::collections::RawArray;

use super::unfair_se_lock::{UnfairSeLock, UnfairSeLockSharedGuard};

/// Multiple-producer single-consumer queue. Generally used in the publicly

/// accessible fields of a component. The holder of this struct should be the

/// consumer. To retrieve access to the producer-side: call `producer()`.

///

/// This is a queue that will resize (indefinitely) if it becomes full, and will

/// not shrink. So probably a temporary thing.

///

/// In debug mode we'll make sure that there are no producers when the queue is

/// dropped. We don't do this in release mode because the runtime is written

/// such that components always remain alive (hence, this queue will remain

/// accessible) while there are references to it.

pub struct QueueDynMpsc<T> {

    // Entire contents are boxed up such that we can create producers that have

    // a pointer to the contents.

    inner: Box<Shared<T>>

}

// One may move around the queue between threads, as long as there is only one

// instance of it.

unsafe impl<T> Send for QueueDynMpsc<T>{}

/// Shared data between queue consumer and the queue producers

struct Shared<T> {

    data: UnfairSeLock<Inner<T>>,

    read_head: AtomicU32,

    write_head: AtomicU32,

    limit_head: AtomicU32,

    #[cfg(debug_assertions)] dbg: AtomicU32,

}

/// Locked by an exclusive/shared lock. Exclusive lock is obtained when the

/// inner data array is resized.

struct Inner<T> {

    data: RawArray<T>,

    compare_mask: u32,

                #[cfg(debug_assertions)] dbg: AtomicU32::new(0),

            }),

        };

    }

    #[inline]

    pub fn producer(&self) -> QueueDynProducer<T> {

        return QueueDynProducer::new(self);

    }

    /// Perform an attempted read from the queue. It might be that some producer

    /// is putting something in the queue while this function is executing, and

    /// we don't get the consume it.

    pub fn pop(&mut self) -> Option<T> {

        let data_lock = self.inner.data.lock_shared();

        let cur_read = self.inner.read_head.load(Ordering::Acquire);

        let cur_limit = self.inner.limit_head.load(Ordering::Acquire);

        let buf_size = data_lock.data.cap() as u32;

        if (cur_read + buf_size) & data_lock.compare_mask != cur_limit {

            // Make a bitwise copy of the value and return it. The receiver is

            // responsible for dropping it.

            unsafe {

                let source = data_lock.data.get((cur_read & data_lock.read_mask) as usize);

                // We can perform a store since we're the only ones modifying

                // the atomic.

                self.inner.read_head.store((cur_read + 1) & data_lock.compare_mask, Ordering::Release);

            }

        } else {

            return None;

        }

    }

}

impl<T> Drop for QueueDynMpsc<T> {

    fn drop(&mut self) {

        // There should be no more `QueueDynProducer` pointers to this queue

        dbg_code!(assert_eq!(self.inner.dbg.load(Ordering::Acquire), 0));

        // And so the limit head should be equal to the write head

        let data_lock = self.inner.data.lock_shared();

        let write_index = self.inner.write_head.load(Ordering::Acquire);

        assert_eq!(self.inner.limit_head.load(Ordering::Acquire), write_index);

        // Every item that has not yet been taken out of the queue needs to

        // have its destructor called. We immediately apply the

        // increment-by-size trick and wait until we've hit the write head.

        let mut read_index = self.inner.read_head.load(Ordering::Acquire);

        read_index += data_lock.data.cap() as u32;

        while read_index & data_lock.compare_mask != write_index {

            unsafe {

                let target = data_lock.data.get((read_index & data_lock.read_mask) as usize);

            read_index += 1;

        }

    }

}

pub struct QueueDynProducer<T> {

    queue: *const Shared<T>,

}

impl<T> QueueDynProducer<T> {

    fn new(consumer: &QueueDynMpsc<T>) -> Self {

        dbg_code!(consumer.inner.dbg.fetch_add(1, Ordering::AcqRel));

        unsafe {

            // If you only knew the power of the dark side! Obi-Wan never told

            // you what happened to your father!

            let queue: *const _ = std::mem::transmute(consumer.inner.as_ref());

            return Self{ queue };

        }

    }

    pub fn push(&self, value: T) {

        let queue = unsafe{ &*self.queue };

        let mut data_lock = queue.data.lock_shared();

        'attempt_write: loop {

            let read_index = queue.read_head.load(Ordering::Acquire);

            if write_index == read_index { // both stored as [0, 2*capacity), so we can check equality without bitwise ANDing

                // Need to resize, try loading read/write index afterwards

                let expected_capacity = data_lock.data.cap();

                data_lock = self.resize(data_lock, expected_capacity);

                write_index = queue.write_head.load(Ordering::Acquire);

                continue 'attempt_write;

            }

            // If here try to advance write index

            let new_write_index = (write_index + 1) & data_lock.compare_mask;

            if let Err(actual_write_index) = queue.write_head.compare_exchange(

                write_index, new_write_index, Ordering::AcqRel, Ordering::Acquire

            ) {

                write_index = actual_write_index;

                continue 'attempt_write;

            }

            // We're now allowed to write at `write_index`

            unsafe {

                std::ptr::write(data_lock.data.get((write_index & data_lock.read_mask) as usize), value);

            }

            // Update limit head to let reader obtain the written value in a

            // CAS-loop

            while let Err(_) = queue.limit_head.compare_exchange_weak(

            ) {}

            return;

        }

    }

    fn resize(&self, shared_lock: InnerRead<T>, expected_capacity: usize) -> InnerRead<T> {

        drop(shared_lock);

        let queue = unsafe{ &*self.queue };

        {

            let mut exclusive_lock = queue.data.lock_exclusive();

            // We hold the exclusive lock, but someone else might have done the resizing, and so:

            if exclusive_lock.data.cap() == expected_capacity {

                let old_capacity = expected_capacity;

                let new_capacity = 2 * old_capacity;

                assert_correct_capacity(new_capacity);

                // Resize by a factor of two, and make the two halves identical.

                exclusive_lock.data.resize(new_capacity);

                for idx in old_capacity..new_capacity {

                    unsafe {

                        let target = exclusive_lock.data.get(idx);

                        let source = exclusive_lock.data.get(idx - old_capacity);

                        std::ptr::write(target, std::ptr::read(source));

                    }

                }

                // Modify all atomics to reflect that we just resized the

                // underlying buffer. We have that everything between the read

                // index and the write index is readable. And the following

                // preserves that property, while increasing the size from

                // `old_capacity` to `new_capacity`.

                // Note that the addition of `new_capacity` to `write_head` is

                // to ensure the ringbuffer can distinguish the cases where the

                // ringbuffer is full, and when it is empty.

                let mut read_index = queue.read_head.load(Ordering::Acquire);

                let mut write_index = queue.write_head.load(Ordering::Acquire);

                debug_assert_eq!(write_index, queue.limit_head.load(Ordering::Acquire)); // since we have exclusive access

                read_index &= exclusive_lock.read_mask;

                write_index &= exclusive_lock.read_mask;

                let new_capacity = new_capacity as u32;

                    // The readable elements do not wrap around the ringbuffer

                    write_index += new_capacity;

                } else {

                    // The readable elements do wrap around the ringbuffer

                    write_index += old_capacity as u32;

                    write_index += new_capacity;

                }

                queue.read_head.store(read_index, Ordering::Release);

                queue.limit_head.store(write_index, Ordering::Release);

                queue.write_head.store(write_index, Ordering::Release);

                // Update the masks

                exclusive_lock.read_mask = new_capacity - 1;

                exclusive_lock.compare_mask = (2 * new_capacity) - 1;

            }

        }

        // Reacquire shared lock

        return queue.data.lock_shared();

    }

}

impl<T> Drop for QueueDynProducer<T> {

    fn drop(&mut self) {

        dbg_code!(unsafe{ (*self.queue).dbg.fetch_sub(1, Ordering::AcqRel) });

    }

}

// producer end is `Send`, because in debug mode we make sure that there are no

// more producers when the queue is destroyed. But is not sync, because that

// would circumvent our atomic counter shenanigans.

unsafe impl<T> Send for QueueDynProducer<T>{}

#[inline]

fn assert_correct_capacity(capacity: usize) {

    assert!(capacity.is_power_of_two() && capacity < (u32::MAX as usize) / 2);

}

                prod_idx += 1;

                prod_idx %= NUM_PROD;

                prod.push(idx);

            }

            // Retrieve and check again

            for idx in 0..INIT_SIZE {

                let gotten = cons.pop().unwrap();

                assert_eq!(idx, gotten);

            }

            assert!(cons.pop().is_none());

            assert_eq!(queue_size(&cons), INIT_SIZE);

        }

    }

    #[test]

    fn multithreaded_production_and_consumption() {

        use std::sync::{Arc, Mutex};

        // Rather randomized test. Kind of a stress test. We let the producers

        // produce `u64` values with the high bits containing their identifier.

        // The consumer will try receive as fast as possible until each thread

        // has produced the expected number of values.

        fn take_num_thread_idx(number: u64) -> u64 { return (number >> 32) & 0xFFFFFFFF; }

        fn take_num(number: u64) -> u64 { return number & 0xFFFFFFFF; }

        // Span queue and producers

        for _stress_idx in 0..NUM_STRESS_TESTS {

            let mut queue = QueueDynMpsc::new(4);

            let mut producers = Vec::with_capacity(NUM_PROD_THREADS);

            for _idx in 0..NUM_PROD_THREADS {

                producers.push(queue.producer());

            }

            // Start up consume thread and let it spin immediately. Note that it

            // must die last.

            let can_exit_lock = Arc::new(Mutex::new(false));

            let mut held_exit_lock = can_exit_lock.lock().unwrap();

            let consume_handle = {

                let can_exit_lock = can_exit_lock.clone();

                std::thread::spawn(move || {

                    let mut counters = [0u64; NUM_PROD_THREADS];

                    let mut num_done = 0;

                    while num_done != NUM_PROD_THREADS {

                        // Spin until we get something

                        let new_value = loop {

                            if let Some(value) = queue.pop() {

                                break value;

                            }

                        };

                        let thread_idx = take_num_thread_idx(new_value);

                        let counter = &mut counters[thread_idx as usize];

                        assert_eq!(*counter, take_num(new_value)); // values per thread arrive in order

                        *counter += 1;

                        if *counter == NUM_PER_THREAD as u64 {

                            // Finished this one

                            num_done += 1;

                        }

                    }

                    let _exit_guard = can_exit_lock.lock().unwrap();

                })

            };

            // Set up producer threads

            let mut handles = Vec::with_capacity(NUM_PROD_THREADS);

            for prod_idx in 0..NUM_PROD_THREADS {

                let prod_handle = producers.pop().unwrap();

                let handle = std::thread::spawn(move || {

                    for number in 0..NUM_PER_THREAD as u64 {

                        prod_handle.push(base_value + number);

                    }

                });

                handles.push(handle);

            }

            // Wait until all producers finished, then we unlock our held lock and

            // we wait until the consumer finishes

            for handle in handles {

                handle.join().expect("clean producer exit");

            }

            drop(held_exit_lock);

            consume_handle.join().expect("clean consumer exit");

        }

    }

}