当pthread_attr_t不为NULL时? [英] when pthread_attr_t is not NULL?

问题描述

除了 pthread_attr_t 之外，POSIX线程中pthread_create的所有参数都非常容易理解. pthread_attr_t 有什么用途，如何以及何时不被 NULL 初始化? >

我浏览了Linux 手册页.我发现的有关 pthread_attr_t 的描述是:

• 语法:

  int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void*),void *arg);
  

• 说明:

  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.
  

这还不清楚.我也在整个互联网上搜索，也没有清晰的解释.因此，当 pthread_attr_t 不是 NULL 时?

有人可以说明一下吗?高度赞赏所有评论和反馈.

解决方案

除其他属性外，您可以使用它来创建分离的(不可联接)线程，或将线程的堆栈大小设置为非默认值.

有关以下内容，请参见POSIX规范:

• 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有两个功能-pthread_attr_destroy()和"set"功能的"get"类似物.)

通常，您不需要修改这些内容.将NULL指针传递给pthread_create()等效于使用默认属性集-这是pthread_attr_init()为您创建的属性.您可以通过函数在pthread_attr_t对象中更改希望更改的属性，然后将该修改后的对象传递给pthread_create().

没有明显理由的另一件事是pthread_t数据类型定义中pthread_create的第一个参数.

所有POSIX线程类型都是不透明的-这是POSIX委员会的蓄意设计决定.您不能随便在类型内部进行戳戳.这使实现更容易-您只能执行功能允许执行的操作.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 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?

I went through the Linux man page. The description I found about pthread_attr_t is:

• Syntax:

  int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void*),void *arg);
  

• 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.
  

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?

Can someone please shed some light about that? All comments and feedback are highly appreciated.

解决方案

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.

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()

(There are two functions per URL — pthread_attr_destroy() and 'get' analogues to the 'set' functions.)

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.

Another thing that there is no apparent justification either, is the first argument from pthread_create on pthread_t data type definition.

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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