什么时候使用系统调用set_tid_address? [英] when is the system call set_tid_address used?

问题描述

我一直试图理解系统调用，并想了解set_tid_address的工作方式.从我所读到的内容来看，基本上是它返回执行的程序或进程的pid.

i have been trying to undertand the system calls, and want to understand how set_tid_address works. bascially from what i have read is that it returns the pid of the program or process which is executed.

我已经用ls进行了测试，但是使用了诸如正常运行时间，top等命令，我看不到使用了set_tid_address.为什么会这样?

I have tested this with ls, however with some commands like uptime, top etc i dont see set_tid_address being used. Why is that?

推荐答案

clone()系统调用可以使用 CLONE_CHILD_CLEARTID 标志，该标志位于 child_tidptr(另一个 clone()参数)被清除，并且相关联的futex在子线程退出时发出唤醒信号.这用于实现 pthread_join()(父线程在futex上等待).

The clone() syscall can take a CLONE_CHILD_CLEARTID flag, that the value at child_tidptr (another clone() argument) gets cleared and an associated futex signal a wake-up when the child thread exits. This is used to implement pthread_join() (the parent thread waits on the futex).

set_tid_address()允许在初始线程上 pthread_join().以下LKML线程中的更多信息:

set_tid_address() allows to pthread_join() on the initial thread. More information in the following LKML threads:

[补丁]线程修复，tid-2.5.47-A3
[补丁] user-vm-unlock-2.5.31-A2

关于为什么某些程序调用 set_tid_address()而其他程序不调用的原因，答案很简单.(直接或间接)链接到libpthread的程序调用 set_tid_address . ls 链接到 librt ，后者链接到 libpthread ，因此它运行NPTL的初始化.

As to why some programs call set_tid_address() and others don't, the answer is easy. Programs linked (directly or indirectly) to libpthread call set_tid_address. ls is linked to librt, which is linked to libpthread, so it runs the initialization for NPTL.

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