Programming

#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

struct xatom {
	short rc;
	pthread_rwlock_t * rwlck;
};
typedef struct xatom xatom;

struct container {
	xatom * atom;
};
typedef struct container container;

#define nr 1
#define nw 2
pthread_t readers[nr];
pthread_t writers[nw];

container * c;

void  retain(container * cont);
void  release(container ** cont);
short retain_count(container * cont);

void * rth(void * arg) {
	short rc;
	while(1) {
		if(c == NULL) break;
		rc = retain_count(c);
	}
	printf("rth exit!\n");
	return NULL;
}

void * wth(void * arg) {
	while(1) {
		if(c == NULL) break;
		release((container **)&c);
	}
	printf("wth exit!\n");
	return NULL;
}

short retain_count(container * cont) {
	short rc = 1;
	pthread_rwlock_rdlock(cont->atom->rwlck);
	printf("got rdlock in retain_count\n");
	rc = cont->atom->rc;
	pthread_rwlock_unlock(cont->atom->rwlck);
	return rc;
}

void retain(container * cont) {
	pthread_rwlock_wrlock(cont->atom->rwlck);
	printf("got retain write lock\n");
	cont->atom->rc++;
	pthread_rwlock_unlock(cont->atom->rwlck);
}

void release(container ** cont) {
	if(!cont || !(*cont)) return;
	container * tmp = *cont;
	pthread_rwlock_t ** lock = (pthread_rwlock_t **)&(*cont)->atom->rwlck;
	pthread_rwlock_wrlock(*lock);
	printf("got release write lock\n");
	if(!tmp) {
		printf("return 2\n");
		pthread_rwlock_unlock(*lock);
		if(*lock) {
			printf("destroying lock 1\n");
			pthread_rwlock_destroy(*lock);
			*lock = NULL;
		}
		return;
	}
	tmp->atom->rc--;
	if(tmp->atom->rc == 0) {
		printf("deallocating!\n");
		*cont = NULL;
		pthread_rwlock_unlock(*lock);
		if(pthread_rwlock_trywrlock(*lock) == 0) {
			printf("destroying lock 2\n");
			pthread_rwlock_destroy(*lock);
			*lock = NULL;
		}
		free(tmp->atom->rwlck);
		free(tmp->atom);
		free(tmp);
	} else {
		pthread_rwlock_unlock(*lock);
	}
}

container * new_container() {
	container * cont = malloc(sizeof(container));
	cont->atom = malloc(sizeof(xatom));
	cont->atom->rwlck = malloc(sizeof(pthread_rwlock_t));
	pthread_rwlock_init(cont->atom->rwlck,NULL);
	cont->atom->rc = 1;
	return cont;
}

int main(int argc, char ** argv) {
	c = new_container();
	int i = 0;
	int l = 4;
	for(i=0;i<l;i++) retain(c);
	for(i=0;i<nr;i++) pthread_create(&readers[i],NULL,&rth,NULL);
	for(i=0;i<nw;i++) pthread_create(&writers[i],NULL,&wth,NULL);
	sleep(2);
	for(i=0;i<nr;i++) pthread_join(readers[i],NULL);
	for(i=0;i<nw;i++) pthread_join(writers[i],NULL);
	return 0;
}