reentrant read lock when writer is trying to acquire lock

reentrant_lock.c

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

pthread_rwlock_t rwlock;

void* writer(void *arg) {
	printf("in writer thread, trying to acquire write lock\n");
	pthread_rwlock_wrlock(&rwlock);
	printf("acquired write lock\n");

	return NULL;
}

int main (int argc, char **argv) {
	// create RWLock
	assert(pthread_rwlock_init(&rwlock, NULL) == 0);

	// acquire read lock
	pthread_rwlock_rdlock(&rwlock);
	printf("read lock acquired\n");

	// reentrant with read
	printf("about to re-acquire read lock\n");
	pthread_rwlock_rdlock(&rwlock);
	printf("reentrant read lock\n");

	// create writer thread
	pthread_t thread;
	assert(pthread_create(&thread, NULL, writer, NULL) == 0);

	// wait for writer to try and acquire write lock
	sleep(1);

	// third reentrant with read
	printf("about to re-acquire read lock for the third time\n");
	pthread_rwlock_rdlock(&rwlock);
	printf("reentrant read lock\n");

	// clean up
	assert(pthread_rwlock_destroy(&rwlock) == 0);
	return 0;
}