当 pthread_attr_t 不为 NULL 时? [英] when pthread_attr_t is not NULL?
问题描述
来自 POSIX 线程的 pthread_create 的所有参数都非常容易理解，除了 pthread_attr_t.pthread_attr_t 是什么，如何以及何时不应由 NULL 初始化?
All parameters for pthread_create from POSIX threads are pretty straightforward to understand, except pthread_attr_t. What is pthread_attr_t for, how, and when it is supposed to be not initialized by NULL?
我浏览了 Linux 手册页.我找到的关于 pthread_attr_t 的描述是:
I went through the Linux man page. The description I found about pthread_attr_t is:
语法:
int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void*),void *arg);
说明:
Explanation:
The attr argument points to a pthread_attr_t structure whose contents
are used at thread creation time to determine attributes for the new
thread; this structure is initialized using pthread_attr_init(3) and
related functions. If attr is NULL, then the thread is created with
default attributes.
这是非常不清楚的.我还在互联网上搜索了所有内容，也找不到任何明确的解释.那么，什么时候 pthread_attr_t 不是 NULL ?
Which is very unclear. I also googled all over the internet, and no clear explanation to be found anywhere either. So, when pthread_attr_t is not NULL?
有人可以解释一下吗?非常感谢所有评论和反馈.
Can someone please shed some light about that? All comments and feedback are highly appreciated.
推荐答案
您可以使用它来创建一个分离的(不可连接的)线程，或者将线程的堆栈大小设置为非默认值，以及其他属性.
You can use it to created a detached (non-joinable) thread, or to set the thread's stack size to a non-default value, amongst other attributes.
查看 POSIX 规范:
See the POSIX specifications for:
pthread_attr_init()pthread_attr_setdetachstate()pthread_attr_setguardsize()pthread_attr_setinheritsched()pthread_attr_setschedparam()pthread_attr_setschedpolicy()pthread_attr_setscope()pthread_attr_setstack()pthread_attr_setstacksize()
(每个 URL 有两个函数 — pthread_attr_destroy() 和 'get' 类似于 'set' 函数.)
(There are two functions per URL — pthread_attr_destroy() and 'get' analogues to the 'set' functions.)
大多数情况下，您不需要修改这些.将 NULL 指针传递给 pthread_create() 等效于使用一组默认属性 — 这是 pthread_attr_init() 为您创建的.您可以通过函数在 pthread_attr_t 对象中更改您希望更改的属性，然后将修改后的对象传递给 pthread_create().
Most often, you don't need to modify these. Passing a NULL pointer to pthread_create() is equivalent to using a default set of attributes — which is what pthread_attr_init() creates for you. You can change the attributes that you wish to change in the pthread_attr_t object via the functions and then pass that modified object to pthread_create() instead.
另一件事也没有明显的理由，是 pthread_create 中 pthread_t 数据类型定义的第一个参数.
Another thing that there is no apparent justification either, is the first argument from
pthread_createonpthread_tdata type definition.
所有 POSIX 线程类型都是不透明的——这是 POSIX 委员会的一个深思熟虑的设计决定.您无法在类型内部随意移动.这使得实现更容易——你只能做函数允许你做的事情.最终，它也简化了程序员(用户)的生活；您不会被欺骗使用不会迁移到其他系统的 POSIX 实现的内部知识.
All the POSIX thread types are opaque — that was a deliberate design decision by the POSIX committees. You can't poke around inside the type portably. This makes it easier for the implementation — you can only do what the functions allow you to do. Ultimately, it simplifies life for the programmers (users) too; you don't get tricked into using internal knowledge of the POSIX implementation that won't migrate to other systems.
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