Pthread lifetimes in linux

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My own tests, as well as numerous web sources, show that all detached child threads die when the main thread exits or is killed (unless it exits with pthread_exit).
c - main thread exit, does other exit too? - Stack Overflow[^]

My question is, has this always been the specified behaviour? or could it have been different in old (10+ years) embedded Linux versions?

Thanks

PS
The reason for my asking is that I am digging into some legacy code that makes the opposite assumption. I want to know if the original writer was mistaken, or if I have missed something.

What I have tried:

I have not found anything an a (historically) different behavior.

Posted 10-Jan-17 1:56am

megaadam

Updated 10-Jan-17 22:49pm

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Jochen Arndt · Accepted Answer · 2017-01-10T02:38:00

Solution 1

An interesting question. I have not a final answer but some hopefully useful information.

The actual behaviour is defined by the POSIX standard (and was so always).

But the Linux kernel uses a different thread model internally. So it had to be changed to provide full pthread compatibilty. See this PDF from 2002: POSIX Threads and the Linux Kernel[^].

The changes has been implemented with kernel version 2.6 (see Native POSIX Thread Library - Wikipedia[^]).

So older kernels used LinuxThreads - Wikipedia[^] which are not POSIX compatible and might behave differently regarding child threads (which did not exist with the LinuxThreads model that uses so called "tasks").

Posted 10-Jan-17 2:38am

Jochen Arndt

Comments

megaadam 10-Jan-17 8:45am

Wow that was quick. Thanks! I will wait a day, before accepting, to see if more clever people have insights to share. :)

Jochen Arndt 10-Jan-17 8:53am

You can accept multiple solutions and rate answers :)

But I understand that accepted questions might not get further answers.

A tip I forgot in my answer:
Check the kernel version that has been used with the old code (if possible).
If it was an old kernel, pthreads hasn't been used and the behaviour is defined by the used thread implementation.

Just recognised that someone has 1-voted your question.
I will counter that. I don't see any reason for a down vote.

megaadam 11-Jan-17 4:50am

Thanks, even if it wasn't conclusive it was giving some insight.
The down-vote prolly came from someone with a "stackoverflowish mindset".

Albert Holguin 11-Jan-17 10:59am

Yeah, it's actually a pretty good question. I'll upvote it as well (as well as your answer).