Порт не освобождается после закрытия приложения

#include <iostream>
#include <string>
#include <cstring>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <signal.h>
#include <thread>
#include <mutex>
#include <set>
#include <chrono>

using namespace std;

class server_exception : public exception {
public:
	string message;
	server_exception(string m) : message(m) {}
};


#define BUF_LEN 1024
#define WITH_MUTEX(mutex, action) {mutex.lock(); action; mutex.unlock();};

bool global_stop_signal = false;

class server {

private:

	bool opened = false;
	set<thread::id> client_threads;
	mutex client_mutex;
	int listener = -1;

	void client(int socket) {
		WITH_MUTEX(client_mutex, client_threads.insert(this_thread::get_id()));
		char buf[BUF_LEN];
		int bytes_readed;
		string message;
		do {
			bytes_readed = recv(socket, (void*)buf, BUF_LEN, 0);
			int signal_on = -1;
			for(int i=0; i<bytes_readed; ++i) {
				if(buf[i] == '\n') {
					signal_on = i;
					break;
				}
			}
			if(signal_on == -1)
				message += buf;
			else {
				if(signal_on != 0 && buf[signal_on - 1] == 13)
					signal_on--;
				for(int i=0; i<signal_on; ++i)
					message += buf[i];
				bytes_readed = 0;
			}
		} while (bytes_readed > 0);
		cout << "message received: \"" << message << "\"" << endl;
		sprintf(buf, "received %d len message\n", static_cast<int>(message.size()));
		send(socket, buf, strlen(buf), 0);
		close(socket);
		WITH_MUTEX(client_mutex, client_threads.erase(this_thread::get_id()));
	}

public:

	void run(unsigned short port) {
		opened = true;
		listener = socket(AF_INET, SOCK_STREAM, 0);
		if(listener < 0) {
			throw server_exception("listener not open");
		}
		sockaddr_in addr;
		bzero((char*)&addr, sizeof(addr));
		addr.sin_family = AF_INET;
		addr.sin_addr.s_addr = INADDR_ANY;
		addr.sin_port = htons(port);
		cout << "connect on " << INADDR_ANY << " " << port << endl;
		if(bind(listener, (sockaddr*) &addr, sizeof(addr)) < 0) {
			throw server_exception("bind error");
		}
		// now on port
		listen(listener, 10);
		for(;;) {
			if(global_stop_signal) {
				return;
			}
			// use accept4(listener, NULL, NULL, SOCK_NONBLOCK)
			int socket = accept(listener, NULL, NULL);
			if(socket < 0) {
				throw server_exception("accept error");
			} else {	
				thread client_thread(&server::client, this, socket);
				client_thread.detach();
			}
		}
	}
	~server() {
		if(opened)
			stop();
	}
	void stop() {
		if(!opened)
			return;
		opened = false;
		cerr << "close call" << endl;
		while(client_threads.size() > 0)
			this_thread::sleep_for(chrono::milliseconds(100));
		if(listener >= 0)
			close(listener);
	}
};

void ctrl_c_event(int _) {
	global_stop_signal = true;
}

int main() {

	struct sigaction handler;

	handler.sa_handler = ctrl_c_event;
	sigemptyset(&handler.sa_mask);
	handler.sa_flags = 0;

	sigaction(SIGINT, &handler, NULL);

	server serv;
	try {
		serv.run(8080);
	} catch (server_exception exc) {
		cout << "exception: " << exc.message << endl;
	}
	serv.stop();

	return 0;
}