多线程

#include <iostream>
#include <thread>
#include <mutex>
#include <string>

using namespace std;

string g_write;
mutex mtx;
bool stop = false;

void thread_fun1(int num) {
    while (num) {
        if (mtx.try_lock()) {
            int len = g_write.length();
            if (len % 4 == 0) {
                g_write += 'A';
                num--;
            }
            mtx.unlock();
        }
    }
    stop = true;
}

void thread_fun2() {
    while(1) {
        if (mtx.try_lock()) {
            int len = g_write.length();
            if (stop && len % 4 == 0) {
                mtx.unlock();
                return;
            }
            if (len % 4 == 1) {
                g_write += 'B';
            }
            mtx.unlock();
        }
    }
}
void thread_fun3() {
    while(1) {
        if (mtx.try_lock()) {
            int len = g_write.length();
            if (stop && len % 4 == 0) {
                mtx.unlock();
                return;
            }
            if (len % 4 == 2) {
                g_write += 'C';
            }
            mtx.unlock();
        }
    }
}
void thread_fun4() {
    while(1) {
        if (mtx.try_lock()) {
            int len = g_write.length();
            if (stop && len % 4 == 0) {
                mtx.unlock();
                return;
            }
            if (len % 4 == 3) {
                g_write += 'D';
            }
            mtx.unlock();
        }
    }
}
int main () {
    int in;
    while (cin >> in) {
        thread t1(thread_fun1, in);
        thread t2(thread_fun2);
        thread t3(thread_fun3);
        thread t4(thread_fun4);
        t1.join();
        t2.join();
        t3.join();
        t4.join();
        cout << g_write.c_str() << endl;
        g_write.clear();
        stop = false;
    }
    return 0;
}