尝试用c11的条件变量和mutex写了一个读写锁

大家多多指正哈~

https://github.com/fishCi/c11/blob/master/rwlock.cpp

#include<thread>
#include<mutex>
#include<iostream>
#include<unistd.h>
#include<condition_variable>
using namespace std;
class rwlock {
    private:
        mutex _lock;
        condition_variable _wcon, _rcon;
        unsigned _writer, _reader;
        int _active;
    public:
        void read_lock() {
            unique_lock<mutex> lock(_lock);
            ++_reader;
            while(_active < 0 || _writer > 0)
                _rcon.wait(lock);
            --_reader;
            ++_active;
        }
        void write_lock() {
            unique_lock<mutex> lock(_lock);
            ++_writer;
            while(_active != 0)
                _wcon.wait(lock);
            --_writer;
            _active = -1;
        }
        void unlock() {
            unique_lock<mutex> lock(_lock);
            if(_active > 0) {
                --_active;
                if(_active == 0) _wcon.notify_one();
            }else{
                _active = 0;
                if(_writer > 0) _wcon.notify_one();
                else if(_reader > 0) _rcon.notify_all();
            }

        }
        rwlock():_writer(0),_reader(0),_active(0){
        }
};

void t1(rwlock* rwl) {
    while(1) {
        cout << "I want to write." << endl;
        rwl->write_lock();
        cout << "writing..." << endl;
        sleep(5);
        rwl->unlock();
        sleep(5);
    }
}

void t2(rwlock* rwl) {
    while(1) {
        cout << "t2-I want to read." << endl;
        rwl->read_lock();
        cout << "t2-reading..." << endl;
        sleep(1);
        rwl->unlock();
    }
}

void t3(rwlock* rwl) {
    while(1) {
        cout << "t3-I want to read." << endl;
        rwl->read_lock();
        cout << "t3-reading..." << endl;
        sleep(1);
        rwl->unlock();
    }
}

int main(){
    rwlock* rwl = new rwlock();
    thread th1(t1,rwl);
    thread th2(t2,rwl);
    thread th3(t3,rwl);
    th1.join();
    th2.join();
    th3.join();
    return 0;
}