1、编辑调试代码
#include <stdio.h>
#include <pthread.h>
int global_val = 0;
void *thread1(void *arg){
while(1){
global_val = global_val + 1;
printf("thread1 global_val=%d\n", global_val);
global_val = global_val + 1;
usleep(100);
printf("thread1 global_val=%d\n", global_val);
usleep(100);
}
return NULL;
}
void *thread2(void *arg){
while(1){
global_val = global_val + 1;
printf("thread2 global_val=%d\n", global_val);
usleep(100);
global_val = global_val + 1;
printf("thread2 global_val=%d\n", global_val);
usleep(100);
}
return NULL;
}
2、编译测试代码gcc mutex.c -o mutex -lpthread
3、查看运行结果，图示位置发现问题。结果不正确。
4、上述代码是无锁状态下的运行情况，运行结果与预期的结果不同，出现错误。下面我们加上互斥锁。
#include <stdio.h>
#include <pthread.h>
pthread_mutex_t thread_mutex;
int global_val = 0;
void *thread1(void *arg){
while(1){
pthread_mutex_lock(&thread_mutex);
global_val = global_val + 1;
printf("thread1 global_val=%d\n", global_val);
global_val = global_val + 1;
usleep(100);
printf("thread1 global_val=%d\n", global_val);
usleep(100);
pthread_mutex_unlock(&thread_mutex);
}
return NULL;
}
void *thread2(void *arg){
while(1){
pthread_mutex_lock(&thread_mutex);
global_val = global_val + 1;
printf("thread2 global_val=%d\n", global_val);
usleep(100);
global_val = global_val + 1;
printf("thread2 global_val=%d\n", global_val);
usleep(100);
pthread_mutex_unlock(&thread_mutex);
}
return NULL;
}
int main(void){
pthread_t thread_id1 = 0, thread_id2 = 0;
pthread_mutex_init(&thread_mutex, NULL);
pthread_create(&thread_id1, NULL, thread1, NULL);
pthread_create(&thread_id2, NULL, thread2, NULL);
pthread_join(thread_id1, NULL);
pthread_join(thread_id2, NULL);
return 0;
}
5、保存代码后编译。
6、运行查看结果，与预期的一致。说明互斥锁起到保护临界资源的作用。
