编程练习：使用变量控制多线程调用顺序

/* 
题目：
output "ABCABCABC": threadFunc_A just print "A", threadFunc_B just print "B", threadFunc_C just print "C".
*/


#include <pthread.h>
#include <iostream>
using namespace std;

bool is_A_ok = true;
bool is_B_ok = false;
bool is_C_ok = false;

static void* threadFunc_A(void* param)
{
    int i = 3;
    while(i > 0)
    {
        if(is_A_ok)
        {
           cout<<"A";
           --i;
           is_A_ok = false;
           is_B_ok = true;
        }
    }
    return NULL;
}

static void* threadFunc_B(void* param)
{
    int i = 3;
    while(i > 0)
    {
        if(is_B_ok)
        {
            cout<<"B";
            --i;
            is_B_ok = false;
            is_C_ok = true;
        }
    }
    return NULL;
}

static void* threadFunc_C(void* param)
{
    int i = 3;
    while(i > 0)
    {
        if(is_C_ok)
        {
            cout<<"C";
            --i;
            is_C_ok = false;
            is_A_ok = true;
        }
    }
 
    cout<<endl;
    return NULL;
}

int main(int argc, char *argv[])
{
    int s=0;
   
    pthread_t tA;
    s = pthread_create(&tA, NULL, &threadFunc_A, NULL);;
    if(s!=0)
    {
        cout<<"Error happend: pthread_create, A"<<endl;
        return EXIT_FAILURE;
    }
    pthread_t tB;
    s = pthread_create(&tB, NULL, &threadFunc_B, NULL);;
    if(s!=0)
    {
        cout<<"Error happend: pthread_create, B"<<endl;
        return EXIT_FAILURE;
    }
    pthread_t tC;
    s = pthread_create(&tC, NULL, &threadFunc_C, NULL);;
    if(s!=0)
    {
        cout<<"Error happend: pthread_create, C"<<endl;
        return EXIT_FAILURE;
    }
 
    pthread_join (tA, NULL);
    pthread_join (tB, NULL);
    pthread_join (tC, NULL);
    return EXIT_SUCCESS;
}