Java程序员也要知道一些底层知识
一、Linux操作系统的三种锁机制:互斥锁(metux)、自旋锁(Spin)、信号量
二、互斥锁-C语言使用-Java锁会调用
1)代码编译指令: gcc mutextest.c -o mutextest.out -pthread
2) C语言代码:
#include <stdio.h> #include <stdlib.h> #include <pthread.h> //声明全局变量sharei 和 方法 int sharei = 0; void increase_num(void); // add mutex --定义一个互斥锁并初始化 pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; //主函数 int main() { int ret; pthread_t thread1,thread2,thread3; ret = pthread_create(&thread1,NULL,(void *)&increase_num,NULL); ret = pthread_create(&thread2,NULL,(void *)&increase_num,NULL); ret = pthread_create(&thread3,NULL,(void *)&increase_num,NULL); // join 主线程等待子线程执行完成以后才结束 pthread_join(thread1,NULL); pthread_join(thread2,NULL); pthread_join(thread3,NULL); printf("sharei = %d ",sharei); return 0; } //run void increase_num(void) { long i,tmp; for(i =0;i<=9999;++i) { //上锁 pthread_mutex_lock(&mutex); //不加锁 结果会小于30000 ,加锁以后结果正确=3000 tmp=sharei; tmp=tmp+1; sharei = tmp; //解锁 pthread_mutex_unlock(&mutex); } }
三、自旋锁-C语言使用(Spin)
#include <stdio.h> #include <stdlib.h> #include <pthread.h> int sharei = 0; void increase_num(void); //定义一把自旋锁 pthread_spinlock_t a_lock; int main() { //初始化自旋锁 pthread_spin_init(&a_lock, 0); int ret; pthread_t thread1,thread2,thread3; ret = pthread_create(&thread1,NULL,(void *)&increase_num,NULL); ret = pthread_create(&thread2,NULL,(void *)&increase_num,NULL); ret = pthread_create(&thread3,NULL,(void *)&increase_num,NULL); pthread_join(thread1,NULL); pthread_join(thread2,NULL); pthread_join(thread3,NULL); printf("sharei = %d ",sharei); return 0; } void increase_num(void) { long i,tmp; for(i =0;i<=9999;++i) { // lock spin 自旋 pthread_spin_lock(&a_lock); tmp=sharei; tmp=tmp+1; sharei = tmp; pthread_spin_unlock(&a_lock); } }