东莞网站seo优化托管,网站开发学习视频,有个专门做装修的网站,我的世界做壁纸网站打不开1.linux使用多线程同步的方法1)互斥锁#xff1a;当线程A锁定了互斥变量时#xff0c;线程B再去锁定时就会被挂起#xff0c;直到A解锁。注意#xff1a;当线程要不断的去轮询检查某个条件以判断是否可以操作需同步的数据时#xff0c;可使用条件变量提高效率。demo如下当线程A锁定了互斥变量时线程B再去锁定时就会被挂起直到A解锁。注意当线程要不断的去轮询检查某个条件以判断是否可以操作需同步的数据时可使用条件变量提高效率。demo如下#include #include #include pthread_mutex_t mutex;void *print_msg(void *arg){int i 0;pthread_mutex_lock(mutex); //互斥锁加锁for (i 0; i 20; i){printf( i %d\n, i);usleep(200);}pthread_mutex_unlock(mutex);}int main(){pthread_t id1, id2;pthread_mutex_init(mutex, NULL);pthread_create(id1, NULL, print_msg, NULL);pthread_create(id2, NULL, print_msg, NULL);pthread_join(id1, NULL); //使主线程等待该线程结束后才结束否则主线程很快结束该线程没有机会执行pthread_join(id2, NULL);pthread_mutex_destroy(mutex);return 0;}2)信号量实际是一个整数只要信号量的value大于0其他线程就可以sem_wait成功成功后信号量的value减1。若value值不大于0则sem_wait使得线程阻塞直到sem_post释放后value值加1,但是sem_wait返回之前还是会将此value值减1。demo如下#include #include #include #include #include #include void *thread_func(void* msg);sem_t sem;sem_t sem_add;#define MSG_SIZE 512int main(){int res -1;pthread_t thread;void *thread_result NULL;char msg[MSG_SIZE];res sem_init(sem, 0, 0);if (res -1){printf(sem init failed\n);exit(-1);}res sem_init(sem_add, 0, 1);if (res -1){printf(sem_add init failed\n);exit(-1);}res pthread_create(thread, NULL, thread_func, msg);if (res ! 0){printf(pthread_create failed\n);exit(-1);}printf(input some text. Enter end to finish...\n);sem_wait(sem_add);while(strcmp(end\n, msg) ! 0){if (strncmp(msg, TEST, 4) 0){strcpy(msg, copy_data\n);sem_post(sem);sem_wait(sem_add);}fgets(msg, MSG_SIZE, stdin);sem_post(sem); //sem信号量加1让子线程开始执行sem_wait(sem_add); //sem_add信号量减1等待子线程处理完成}printf(waiting for thread to finish...\n);res pthread_join(thread, thread_result);if (res ! 0){printf(pthread_join faild\n);exit(-1);}printf(thread joined\n);sem_destroy(sem);sem_destroy(sem_add);exit(0);return 0;}void* thread_func(void* msg){char *ptr (char*)msg;sem_wait(sem);while(strcmp(end\n, ptr) ! 0){int i 0;for (; ptr[i] ! \0; i ){if (ptr[i] a ptr[i] z){ptr[i] - a - A;}}printf(you input %d characters\n, i - 1);printf(to uppercase: %s\n, ptr);sem_post(sem_add);sem_wait(sem);}sem_post(sem_add);pthread_exit(NULL);}3)条件变量经常和互斥锁一起使用使用时条件变量被用来阻塞一个线程当条件不满足时线程会解开相应的互斥锁并等待条件发生变化一旦其他的某个线程改变了条件变量它将通知相应的条件变量唤醒一个或多个正被此变量阻塞的线程这些线程将重新锁定互斥锁并重新测试条件是否满足。pthread_cont_init()pthread_cont_destroy()pthread_cont_wait() //线程解开mutex指向的锁并被条件变量阻塞pthread_cont_timedwait() //多了时间参数当时间过了以后即使条件变量不满足阻塞也被解除pthread_cont_signal()/pthread_cont_broadcast //唤醒被条件变量阻塞的线程。demo如下pthread1(){pthread_mutex_lock(lock_s);sum;pthread_mutex_unlock(lock_s);if (sum 100){pthread_cond_signal(cond_sum_ready);//先发送一次}}pthread2(){pthread_mutex_lock(lock_s);while(sum 100){pthread_cond_wait(cond_sum_ready, lock_s);//会先执行pthread_MUTEX_UNLOCK进行解锁然后休眠}sum 0;pthread_mutex_unlock(lock_s);}注意最终哪个线程接收到信号根据优先级来4)读写锁可以多个线程同时占用读模式的读写锁但是只能一个线程占用写模式的读写锁。当读写锁是写加锁状态时在这个锁被解锁前所有试图对这个锁加锁的线程都会被阻塞当读写锁是读加锁状态时其他线程可以读模式得到访问权但是以写模式对它进行加锁的线程都将被阻塞当读写锁是在读模式加锁状态时如果有其他线程试图以写模式加锁读写锁通常会阻塞随后的读模式锁请求避免读模式锁长期占用而写模式所长期阻塞读写锁适用于对数据读的次数比写的次数多的情况。API接口初始化和销毁int pthread_rwlock_init();int pthread rwlock_destroy();读加锁、写加锁、解锁pthread_rwlock_rdlock();pthread_rwlock_wrlock();pthread_rwlock_unlock();非阻塞获得读锁和写锁pthread_rwlock_tryrdlock();pthread_rwlock_trywrlock();demo如下#include #include #include #define Read_Num 2pthread_rwlock_t lock;class Data{public:Data(int i, float f): I(i), F(f){}int GetI(){return I;}float GetF(){return F;}private:int I;float F;};Data *pData NULL;void *read(void *arg){int *id (int*)arg;while(true){pthread_rwlock_rdlock(lock);printf( reader %d is reading data\n, *id);if (pData NULL){printf(data is NULL\n);}else{printf(data: I %d, F %f\n, pData-GetI(), pData-GetF());}pthread_rwlock_unlock(lock);}pthread_exit(0);}void *write(void *arg){while(true){pthread_rwlock_wrlock(lock); //写锁加锁后解锁前所有试图对该锁加锁的线程都会被堵塞printf(writer is wiriting data:\n);if (pData NULL){pData new Data(2, 2.2);printf(writer is writing data: %d, %f\n, pData-GetI(), pData-GetF());}else{delete pData;pData NULL;printf(wirter free the data\n);}pthread_rwlock_unlock(lock);}pthread_exit(0);}int main(){pthread_t reader[Read_Num];pthread_t writer;for (int i 0; i Read_Num; i){pthread_create(reader[i], NULL, read, (void*)i);}pthread_create(writer, NULL, write, NULL);while(1){sleep(1);}return 0;}2.信号量和互斥锁之间的区别互斥锁用于互斥对资源的访问是无序的信号量用于同步对资源的访问是有序的互斥量的加锁和解锁必须由同一线程对应使用而信号量可以由一个线程释放另一个线程得到3.什么情况下会产生死锁以及怎样避免死锁比如线程A对资源M加锁去申请资源N线程B对资源N加锁去申请资源M此种情况下会产生死锁要有效的避免死锁可使用银行家算法线程A和B在使用资源的时候按照同一顺序即加锁时按照同一顺序这样就可以避免死锁。
