th.c

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

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <errno.h>


int levee_dialer_fds[2];
int levee_dialer_rc;


struct levee_dialer_request {
	uint16_t node_len;
	uint16_t service_len;
	int type;
	int no;
};


struct levee_dialer_response {
	int err;
	int eai;
	int no;
};


void *
levee_dialer_loop(void *arg) {
	int rc;

	struct levee_dialer_request req;
	struct levee_dialer_response res;

	char node[8096];
	char service[1024];

	struct addrinfo hints, *info, *ptr;

	int no;
	int err;

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = AF_INET;
	hints.ai_socktype = SOCK_STREAM;

	while(1) {
		memset(&res, 0, sizeof(res));

		rc = read(levee_dialer_fds[0], &req, sizeof(req));
		assert(rc == sizeof(req));

		rc = read(levee_dialer_fds[0], node, req.node_len);
		assert(rc == req.node_len);
		node[req.node_len] = 0;

		rc = read(levee_dialer_fds[0], service, req.service_len);
		assert(rc == req.service_len);
		service[req.service_len] = 0;

		rc = getaddrinfo(node, service, &hints, &info);
		if (rc != 0) {
			res.eai = rc;
			goto respond;
		}

		no = socket(PF_INET, req.type, 0);
		if (no < 0) {
			res.err = errno;
			goto respond;
		}

		for (ptr = info; ptr; ptr = ptr->ai_next) {
			rc = connect(no, ptr->ai_addr, ptr->ai_addrlen);
			if (rc == 0) break;
			err = errno;
		}

		freeaddrinfo(info);

		if (ptr == NULL) {
			res.err = err;
		} else {
			res.no = no;
		}

		respond:
		rc = write(req.no, &res, sizeof(res));
		assert(rc == sizeof(res));
	}
}


int levee_dialer_boot(void) {
	pthread_t thr;
	pthread_attr_t attr;
	int rc;

	rc = pipe(levee_dialer_fds);
	if (rc != 0) return errno;

	rc = pthread_attr_init (&attr);
	if (rc != 0) return errno;
	rc = pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
	if (rc != 0) return errno;
	rc = pthread_create (&thr, &attr, &levee_dialer_loop, NULL);
	if (rc != 0) return errno;

	return 0;
}


pthread_once_t levee_dialer_once = PTHREAD_ONCE_INIT;


void levee_dialer_run_once(void) {
	levee_dialer_rc = levee_dialer_boot();
}


int levee_dialer_init(void) {
	pthread_once(&levee_dialer_once, levee_dialer_run_once);
	return levee_dialer_rc;
}


int
writer(const char *node, const char *service) {
	int rc;

	struct levee_dialer_request req;
	struct levee_dialer_response res;

	int fds[2];
	rc = pipe(fds);
	if (rc != 0) return errno;

	req.node_len = (uint16_t) strlen(node);
	req.service_len = (uint16_t) strlen(service);
	req.type = SOCK_STREAM;
	req.no = fds[1];

	rc = write(levee_dialer_fds[1], &req, sizeof(req));
	assert(rc == sizeof(req));

	rc = write(levee_dialer_fds[1], node, strlen(node));
	assert(rc == strlen(node));

	rc = write(levee_dialer_fds[1], service, strlen(service));
	assert(rc == strlen(service));

	rc = read(fds[0], &res, sizeof(res));
	assert(rc == sizeof(res));

	printf("%s \\ %s \\ %d\n", gai_strerror(res.eai), strerror(res.err), res.no);
	return 0;
}


int main(int argc, char **argv)
{
	levee_dialer_init();
	writer("localhost", "8000");
	writer("localhost", "8080");
	writer("ldld", "8080");
	return 0;
}

These should be declared static: https://gist.github.com/cablehead/f3f4863d8c5647bda5606490ca959554#file-th-c-L14-L15. Technically, that will happen anyway, but its safer. Without static I would typically assume there is an extern in the header for them, giving them external linkage.