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/**
* @file sem.c
* @author Hanjie Wu (hanjiew)
* @author Devang Acharya (devanga)
* @brief Semaphore implementation
* @date 2023-02-22
*
*/
#include <sem.h>
/**
* @brief Initializes the semaphore pointed to by 'sem' tp value 'count'
*
* @param sem semaphore
* @param count count
* @return int
*/
int sem_init(sem_t* sem, int count) {
sem->value = count;
mutex_init(&sem->value_lock);
cond_init(&sem->value_cv);
return 0;
}
/**
* @brief Decrement sem value, may block until it is possible to do so
*
* @param sem semaphore
*/
void sem_wait(sem_t* sem) {
mutex_lock(&sem->value_lock);
while (sem->value <= 0) {
/* wait until value goes up */
cond_wait(&sem->value_cv, &sem->value_lock);
}
sem->value -= 1;
mutex_unlock(&sem->value_lock);
}
/**
* @brief wake up a thread waiting on the semaphore pointed to by sem
*
* @param sem semaphore
*/
void sem_signal(sem_t* sem) {
mutex_lock(&sem->value_lock);
sem->value += 1;
if (sem->value == 1) {
/* notify when value goes up from zero */
cond_signal(&sem->value_cv);
}
mutex_unlock(&sem->value_lock);
}
/**
* @brief deactivate semaphore. Must not be called on semaphores bwing waited
* upon
*
* @param sem semaphore
*/
void sem_destroy(sem_t* sem) {
mutex_destroy(&sem->value_lock);
cond_destroy(&sem->value_cv);
}
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