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

    pub struct Condvar {
        pub inner: UPIntrFreeCell<CondvarInner>,
    }

    pub struct CondvarInner {
        pub wait_queue: VecDeque<Arc<TaskControlBlock>>,
    }

    impl Condvar {
        pub fn new() -> Self {
            Self {
                inner: unsafe {
                    UPIntrFreeCell::new(CondvarInner {
                        wait_queue: VecDeque::new(),
                    })
                },
            }
        }

        pub fn signal(&self) {
            let mut inner = self.inner.exclusive_access();
            if let Some(task) = inner.wait_queue.pop_front() {
                add_task(task);
            }
        }

        /*
        pub fn wait(&self) {
            let mut inner = self.inner.exclusive_access();
            inner.wait_queue.push_back(current_task().unwrap());
            drop(inner);
            block_current_and_run_next();
        }
        */

        pub fn wait_no_sched(&self) -> *mut TaskContext {
            self.inner.exclusive_session(|inner| {
                inner.wait_queue.push_back(current_task().unwrap());
            });
            block_current_task()
        }

        pub fn wait_with_mutex(&self, mutex: Arc<dyn Mutex>) {
            mutex.unlock();
            self.inner.exclusive_session(|inner| {
                inner.wait_queue.push_back(current_task().unwrap());
            });
            block_current_and_run_next();
            mutex.lock();
        }
    }