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    use crate::sync::UPIntrFreeCell;
    use crate::task::{add_task, block_current_and_run_next, current_task, TaskControlBlock};
    use alloc::{collections::VecDeque, sync::Arc};

    pub struct Semaphore {
        pub inner: UPIntrFreeCell<SemaphoreInner>,
    }

    pub struct SemaphoreInner {
        pub count: isize,
        pub wait_queue: VecDeque<Arc<TaskControlBlock>>,
    }

    impl Semaphore {
        pub fn new(res_count: usize) -> Self {
            Self {
                inner: unsafe {
                    UPIntrFreeCell::new(SemaphoreInner {
                        count: res_count as isize,
                        wait_queue: VecDeque::new(),
                    })
                },
            }
        }

        pub fn up(&self) {
            let mut inner = self.inner.exclusive_access();
            inner.count += 1;
            if inner.count <= 0 {
                if let Some(task) = inner.wait_queue.pop_front() {
                    add_task(task);
                }
            }
        }

        pub fn down(&self) {
            let mut inner = self.inner.exclusive_access();
            inner.count -= 1;
            if inner.count < 0 {
                inner.wait_queue.push_back(current_task().unwrap());
                drop(inner);
                block_current_and_run_next();
            }
        }
    }