Question

我编写了以下代码，其中父代创建了一个共享内存对象，然后调用fork系统调用API来创建子进程。正如预期的那样，我面临着不一致的问题，因为它们都会使用共享内存对象，并且会出现竞争条件。我不明白的是，当我在单处理器上运行任务集的过程时，没有竞争条件？这种行为背后的原因可能是什么？

//init Attachmem as shared memory object having countval as a member
 int main(){
        pid_t retval;                       
        int status;                         
        retval=fork();                          
        if(retval<0){                           
            perror("Fork failed\n");
            exit(1);
        }

    printf("When Parent donot waits for child \n\n\n");
    if(retval>0){                           
        while(dummycount){                  
            Attachmem->countval++;              
            dummycount--;
        }
        printf("PARENT::In parent context value of Countval becomes %d\n",Attachmem->countval); //shared object
        printf("PARENT::In parent context value of dummycount  becomes %d \n",dummycount);  //parent specific object
    }   
    if(retval==0){                          
        dummycount=0;
        while(Attachmem->countval){             
            dummycount++;       

        }
        printf("CHILD::In child context the value of Countval  becomes %d\n",Attachmem->countval);
        printf("CHILD::In child context the value of dummycount becomes %d\n",dummycount);
        error(0);
    }


 return 0;
}

输出:: 当孩子和家长在不同的处理器上运行时

CHILD::In child context the value of Countval  becomes 0
CHILD::In child context the value of dummycount becomes 16897
./a.out: : Unknown error 16897
PARENT::In parent context value of Countval becomes 479145
PARENT::In parent context value of dummycount  becomes 0

当子级和父级使用任务集在同一处理器上运行时

PARENT::In parent context value of Countval becomes 500000
PARENT::In parent context value of dummycount  becomes 0 
When Parent donot waits for child 


CHILD::In child context the value of Countval  becomes 0
CHILD::In child context the value of dummycount becomes 500000
./a.out: : Unknown error 500000

我目前正在使用linux内核3.16.6运行OpenSuse

单处理器上共享内存的竞争条件？

0 个答案: