Thread: question about semaphores

Code:

typedef struct {
    int buf[BUFF_SIZE];   /* shared var */
    int in;         	  /* buf[in%BUFF_SIZE] is the first empty slot */
    int out;        	  /* buf[out%BUFF_SIZE] is the first full slot */
    sem_t full;     	  /* keep track of the number of full spots */
    sem_t empty;    	  /* keep track of the number of empty spots */
    sem_t mutex;    	  /* enforce mutual exclusion to shared data */
} sbuf_t;

sbuf_t shared;



int main()
{
    pthread_t idP, idC;
    int index;

    sem_init(&shared.full, 0, 0);
    sem_init(&shared.empty, 0, BUFF_SIZE);

At the red lines,I dont understand why the value of shared.full is 0 and the value of shared.empty is BUFF_SIZE. I need some explanations. Thanks

Well sem_init full is a counter. I believe your comment for this was enough, so I am not sure where your confusion may be with that. This is just the initial value being used. As far as sem_init() making use of the constant BUFF_SIZE, this may be due to the fact that the function call is using this value argument and subtracting from this.


Have you read up on this call?
sem_init