Understanding Pthreads

Question

I came across a concept in Advanced Linux Programming. Here\'s a link: refer to 4.5 GNU/Linux Thread Implementation.

I\'m clear wit

Answer 1

I get the same results of the book with linux that contains the libc libuClibc-0.9.30.1.so (1).

root@OpenWrt:~# ./test
main thread pid is 1151
child thread pid is 1153

and I tried to run this program with a linux that contains the libc from ubuntu libc6 (2)

$ ./test
main thread pid is 2609
child thread pid is 2609

The libc (1) use linuxthreads implementation of pthread

And the libc (2) use NPTL ("Native posix thread library") implementation of pthread

According to the linuxthreads FAQ (in J.3 answer):

each thread is really a distinct process with a distinct PID, and signals sent to the PID of a thread can only be handled by that thread

So in the old libc which use linuxthreads implementation, each thread has its distinct PID

In the new libc version which use NPTL implementation, all threads has the same PID of the main process.

The NPTL was developed by redhat team. and according to the redhat NPTL document: One of the problems which are solved in the NPTL implementation is:

(Chapter: Problems with the Existing Implementation, page5)

Each thread having a different process ID causes compatibility problems with other POSIX thread implementations. This is in part a moot point since signals can'tbe used very well but is still noticeable

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And that explain your issue.

You are using the new libc version that contains the NPTL ("Native posix thread library") implementation of pthread

And the Book use an old version of libc that contains linuxthreads implementation of pthread