我正在学习 C 中的 pthreads,我开始编写非常愚蠢的程序来掌握它们。我试图创建一个包含两个线程的程序,它们应该打印它们的名称,并且在它们终止执行时应该收集它们的状态。所以我的代码是:
//Function declaration
void *state_your_name(char*);
//Function definition
//Passing a string as parameter for
//outputting the name of the thread
void *state_your_name(char *name) {
//Declaration of the variable containing the return status
void* status;
//Printing out the string
printf("%s\n", name);
//Exiting the thread and saving the return value
pthread_exit(status);
}
int main(void) {
pthread_t tid_1, tid_2;
void * status;
//Creating thread 1...
if (pthread_create(&tid_1, NULL, state_your_name, "Thread 1")) {
printf("Error creating thread 1");
exit(1);
}
//Creating thread 2...
if (pthread_create(&tid_2, NULL, state_your_name, "Thread 2")) {
printf("Error creating thread 2");
exit(1);
}
//Waiting for thread 1 to terminate and
//collecting the return value...
if (pthread_join(tid_1, (void *) &status)) {
printf("Error joining thread 1");
exit(1);
}
printf("Thread 1 - Return value: %d\n", (int)status );
//Waiting for thread 2 to terminate and
//collecting the return value...
if (pthread_join(tid_2, (void *) &status)) {
printf("Error joining thread 2");
exit(1);
}
printf("Thread 2 - Return value: %d\n", (int)status );
return 0;
}
我希望得到这样的输出:
Thread 1
Thread 2
Thread 1 - Return value: 0
Thread 2 - Return value: 0
但我的问题是 Thread 1
的返回值是 733029576
,但是 Thread 2
返回 0
预料到的;就像状态变量未初始化并且包含垃圾一样。我错过了什么?
最佳答案
您在输出中看到垃圾值的原因是 state_your_name
的本地 void *status
变量未初始化:
void *state_your_name(char *name) {
//Declaration of the variable containing the return status
void* status = NULL; // <<===== Add initialization here
//Printing out the string
printf("%s\n", name);
//Exiting the thread and saving the return value
pthread_exit(status);
}
进行此更改后,您的程序应该会产生您期望的输出。
请注意,直接从 state_your_name
返回 status
是调用 pthread_exit
的替代方法:您可以用 return status< 替换该调用
.
关于c - 线程终止后返回值错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17028729/