/*
* Disposes of the specified semaphore.
*/
ret_t ksema_free(struct ksema *sem)
{
unsigned long eflags;
disable_hwint(eflags);
if (!list_empty(sem->waiting_task_list_head)) {
restore_hwint(eflags);
return -E_BUSY;
}
kfree(sem);
restore_hwint(eflags);
return S_OK;
}
void rs_putchar(char ch)
{
eflags_t eflags;
disable_hwint(eflags);
while (!is_transmit_empty());
out_byte(PORT, ch);
restore_hwint(eflags);
}
/*
* Implements the DOWN operation on the specified kernel semaphore.
* Do not call this function from an interrupt handler!
*/
void ksema_down(struct ksema *sem)
{
unsigned long eflags;
disable_hwint(eflags);
if (!sem->value) {
/* Append the current task to the semaphore's wait queue and sleep. */
list_append(sem->waiting_task_list_head, current);
current->state = TASK_UNINTERRUPTIBLE;
schedule();
}
/* Decrement the value of the semaphore. */
sem->value--;
restore_hwint(eflags);
}
/*
* Implements the UP operation on the specified kernel semaphore.
*/
void ksema_up(struct ksema *sem)
{
unsigned long eflags;
struct task_struct *t;
disable_hwint(eflags);
/* Increment the value of the semaphore. */
sem->value++;
/* Remove the first task from the semaphore's wait queue and wake it up! */
if (!list_empty(sem->waiting_task_list_head)) {
t = list_pop_head(sem->waiting_task_list_head);
t->state = TASK_RUNNABLE;
}
restore_hwint(eflags);
}