1、如何利用2个条件变量实现线程同步？
思路：就是来回的利用pthread_cond_signal()函数，当一方被阻塞时，唤醒函数可以唤醒pthread_cond_wait()函数，只不过pthread_cond_wait()这个方法要执行其后的语句，必须遇到下一个阻塞(也就是pthread_cond_wait()方法时)，才执行唤醒后的其后语句。
代码如下：
#include#include #include #include #include #define MAX_NUM 2static int count = 1;pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;pthread_cond_t js = PTHREAD_COND_INITIALIZER;pthread_cond_t os = PTHREAD_COND_INITIALIZER;void* A(void *arg){ pthread_mutex_lock(&mutex); while(count <= MAX_NUM){ if(count%2 == 1){ printf("A = %d\n", count); count++; pthread_cond_signal(&os); sleep(5); printf("bbbbbbbbbbbbbbbbbbbbbbbbbbb\n"); }else{ printf("ccccccccccccccccccccccccccc\n"); pthread_cond_wait(&js, &mutex); printf("ddddddddddddddddddddddddddd\n"); } pthread_mutex_unlock(&mutex); }}void* B(void *arg){ pthread_mutex_lock(&mutex); while(count <= MAX_NUM){ if(count%2 == 0){ printf("B = %d\n", count); count++; pthread_cond_signal(&js); }else{ pthread_cond_wait(&os, &mutex); printf("aaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"); } } pthread_mutex_unlock(&mutex);}int main(void){ pthread_t tid1, tid2; pthread_create(&tid2, NULL, B, NULL); sleep(1); pthread_create(&tid1, NULL, A, NULL); pthread_join(tid1, NULL); pthread_join(tid2, NULL); return 0;}
运行结果
上面的这个程序就是：2个条件变量对一个互斥量的操作。signal()发送唤醒wait()，wait()之后的语句暂时不执行，直到下一次遇到wait()时，阻塞，返回执行唤醒的wait()之后的语句。
2、怎么创建10个线程的开始运行和结束过程？
利用2个条件变量和1个互斥量即可实现。
代码如下：
#include#include #include #include #include pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;pthread_cond_t cond = PTHREAD_COND_INITIALIZER;pthread_cond_t cond1 = PTHREAD_COND_INITIALIZER;void* thread_fun1(void *arg){ int i = *(int *)arg; pthread_mutex_lock(&mutex); printf("[%d] thread start up\n", i); pthread_cond_wait(&cond, &mutex); printf("[%d]thread is wake up\n", i); pthread_mutex_unlock(&mutex);}void* thread_fun2(void *arg){ pthread_cond_broadcast(&cond); //广播，一次唤醒所有的线程}int main(void){ pthread_t tid1[10], tid2; int i; for(i = 0; i < 10; i++){ pthread_create(&tid1[i], NULL, thread_fun1, &i);//创建10个线程 sleep(1); } pthread_create(&tid2, NULL, thread_fun2, NULL);//创建1个线程 for(i = 0; i < 10; i++){ //主线程等子线程执行完 pthread_join(tid1[i], NULL); } pthread_join(tid2, NULL); return 0;}
运行结果
多线程的编程中：互斥量、条件变量是重中之重！！！