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    mod context;
    mod id;
    mod manager;
    mod process;
    mod processor;
    mod signal;
    mod switch;
    #[allow(clippy::module_inception)]
    mod task;

    use crate::fs::{open_file, OpenFlags};
    use alloc::sync::Arc;
    use lazy_static::*;
    use manager::fetch_task;
    use process::ProcessControlBlock;
    use switch::__switch;

    pub use context::TaskContext;
    pub use id::{kstack_alloc, pid_alloc, KernelStack, PidHandle};
    pub use manager::{add_task, pid2process, remove_from_pid2process};
    pub use processor::{
        current_kstack_top, current_process, current_task, current_trap_cx, current_trap_cx_user_va,
        current_user_token, run_tasks, schedule, take_current_task,
    };
    pub use signal::SignalFlags;
    pub use task::{TaskControlBlock, TaskStatus};

    pub fn suspend_current_and_run_next() {
        // There must be an application running.
        let task = take_current_task().unwrap();

        // ---- access current TCB exclusively
        let mut task_inner = task.inner_exclusive_access();
        let task_cx_ptr = &mut task_inner.task_cx as *mut TaskContext;
        // Change status to Ready
        task_inner.task_status = TaskStatus::Ready;
        drop(task_inner);
        // ---- release current TCB

        // push back to ready queue.
        add_task(task);
        // jump to scheduling cycle
        schedule(task_cx_ptr);
    }

    pub fn block_current_and_run_next() {
        let task = take_current_task().unwrap();
        let mut task_inner = task.inner_exclusive_access();
        let task_cx_ptr = &mut task_inner.task_cx as *mut TaskContext;
        task_inner.task_status = TaskStatus::Blocking;
        drop(task_inner);
        schedule(task_cx_ptr);
    }

    pub fn exit_current_and_run_next(exit_code: i32) {
        let task = take_current_task().unwrap();
        let mut task_inner = task.inner_exclusive_access();
        let process = task.process.upgrade().unwrap();
        let tid = task_inner.res.as_ref().unwrap().tid;
        // record exit code
        task_inner.exit_code = Some(exit_code);
        task_inner.res = None;
        // here we do not remove the thread since we are still using the kstack
        // it will be deallocated when sys_waittid is called
        drop(task_inner);
        drop(task);
        // however, if this is the main thread of current process
        // the process should terminate at once
        if tid == 0 {
            remove_from_pid2process(process.getpid());
            let mut process_inner = process.inner_exclusive_access();
            // mark this process as a zombie process
            process_inner.is_zombie = true;
            // record exit code of main process
            process_inner.exit_code = exit_code;

            {
                // move all child processes under init process
                let mut initproc_inner = INITPROC.inner_exclusive_access();
                for child in process_inner.children.iter() {
                    child.inner_exclusive_access().parent = Some(Arc::downgrade(&INITPROC));
                    initproc_inner.children.push(child.clone());
                }
            }

            // deallocate user res (including tid/trap_cx/ustack) of all threads
            // it has to be done before we dealloc the whole memory_set
            // otherwise they will be deallocated twice
            for task in process_inner.tasks.iter().filter(|t| t.is_some()) {
                let task = task.as_ref().unwrap();
                let mut task_inner = task.inner_exclusive_access();
                task_inner.res = None;
            }

            process_inner.children.clear();
            // deallocate other data in user space i.e. program code/data section
            process_inner.memory_set.recycle_data_pages();
            // drop file descriptors
            process_inner.fd_table.clear();
        }
        drop(process);
        // we do not have to save task context
        let mut _unused = TaskContext::zero_init();
        schedule(&mut _unused as *mut _);
    }

    lazy_static! {
        pub static ref INITPROC: Arc<ProcessControlBlock> = {
            let inode = open_file("initproc", OpenFlags::RDONLY).unwrap();
            let v = inode.read_all();
            ProcessControlBlock::new(v.as_slice())
        };
    }

    pub fn add_initproc() {
        let _initproc = INITPROC.clone();
    }

    pub fn check_signals_of_current() -> Option<(i32, &'static str)> {
        let process = current_process();
        let process_inner = process.inner_exclusive_access();
        process_inner.signals.check_error()
    }

    pub fn current_add_signal(signal: SignalFlags) {
        let process = current_process();
        let mut process_inner = process.inner_exclusive_access();
        process_inner.signals |= signal;
    }