changing thread user context in linux
 

Hi!

I wanted to know whether there is a way in linux to change the user context of *one of the threads* in the process.

I do not want to launch another process using fork or any other method.

I know that on Windows it is possible but don't know if on linux.

Thanks in advance,
-Neel.

Is getcontext and setcontext what you are after?

You can also change the user id with getuid() and setuid().

Thanks for the reply.

I am not sure. here is what I want to do:

- Change context of *only* of thread to some user from root
- use gssapi to fetch the ticket for that user
- change thread context back to root

I believe setcontext/getcontext might be the way to go but I am not sure that it will not change context of rest of the process or even GSSAPI will work with this kind of approach. I will do some trials and find out.. If you do have any further suggestions/comments, they are welcome.

Thanks,
- Neel.

Sorry, I missed your emphasis.

No, it isn't possible to just change one of the threads. The pthreads in *nix systems are light-weight compared to the Windows equivalent, and share more state information. The POSIX standard requires that they share user and group ids.

Incidentally, a fork is much faster than a CreateProcess on Windows (CreateProcess is something more akin to vfork+exec). For a long time fork was the only way to do multitasking in Unix, so it is well optimized for the job. Not sure if that makes it any more palatable?