在pthread_join()和了pthread_exit() [英] pthread_join() and pthread_exit()
问题描述
我有一个关于C并发编程的问题。
I have a question about C concurrency programming.
在pthread库,原型在pthread_join
是
In the pthread library, the prototype of pthread_join
is
int pthread_join(pthread_t tid, void **ret);
和了pthread_exit
的原型是:
void pthread_exit(void *ret);
所以我感到困惑的是,为什么在pthread_join
取过程的返回值作为一个指针到无效
从收割线程指针,但了pthread_exit
只需无效
从退出线程指针?我的意思是基本上他们是从一个线程,为什么在种类的不同所有的返回值?
So I am confused that, why pthread_join
takes the return value of the process as a pointer to a void
pointer from reaped thread, but pthread_exit
only takes a void
pointer from the exited thread? I mean basically they are all return values from a thread, why there is a difference in type?
推荐答案
在了pthread_exit
, RET
是输入参数。你只是传递一个变量的地址的功能。
In pthread_exit
, ret
is an input parameter. You are simply passing the address of a variable to the function.
在在pthread_join
, RET
是一个输出参数。你回来从函数的值。这样的值,例如,设置为 NULL
。
In pthread_join
, ret
is an output parameter. You get back a value from the function. Such value can, for example, be set to NULL
.
龙解释:
在在pthread_join
,你回来了成品线程传递给了pthread_exit
的地址。如果你通过只是一个普通的指针,它是按值传递的,所以你不能改变它指向。为了能够改变传递给在pthread_join指针的值时,它必须作为一个指针本身,也就是说,一指针的指针进行传递。
In pthread_join
, you get back the address passed to pthread_exit
by the finished thread. If you pass just a plain pointer, it is passed by value so you can't change where it is pointing to. To be able to change the value of the pointer passed to pthread_join, it must be passed as a pointer itself, that is, a pointer to a pointer.
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