Re: [Qemu-devel] [PATCH] use a thread id variable

["Glauber Costa" <glommer@gmail.com>]

On Sun, Mar 9, 2008 at 11:52 AM, Gilad Ben-Yossef <gilad@codefidence.com> wrote:
> Jamie Lokier wrote:
>  > Gilad Ben-Yossef wrote:
>  >> Glauber Costa wrote:
>  >>> This patch introduces a "thread_id" variable to CPUState.
>  >>> It's duty will be to hold the process, or more generally, thread
>  >>> id of the current executing cpu
>  >>>
>  >>>     env->nb_watchpoints = 0;
>  >>> +#ifdef __WIN32
>  >>> +    env->thread_id = GetCurrentProcessId();
>  >>> +#else
>  >>> +    env->thread_id = getpid();
>  >>> +#endif
>  >>>     *penv = env;
>  >> hmm... maybe I'm missing something, but in Linux at least I think you
>  >> would prefer this to be gettid() rather then getpid as each CPU has it's
>  >> own thread, not a different process.
>  >
>  > On most platforms, getpid() returns the same value for all threads, so
>  > it's not useful as a thread id.
>
>  Of course it does - this what POSIX says it should do (Linux 2.4 in
>  compliance not withstanding). Which is why I suggested to use on Linux
>  the non standard gettid() rather then getpid
>
> >
>  > On Linux, it depends which version of threads.  The old package,
>  > LinuxThreads, has different getpid() for each thread.  The current one,
>  > NPTL, has them all the same.
>
>
>  LinuxThreads behavior is wrong according to the POSIX standard. Of
>  course, nothing else was possible with 2.4 kernels, so this is not an
>  error on LinuxThreads coders part.
>
>
>
>  > What you're supposed to do with pthreads in general is use pthread_self().
>
>  Unfortunately, AFAIK the opaque handle that pthread_self() returns is
>  not  quite meaningless outside of the process whereas what the non
>  standard gettid() returns can actually be used to identify a thread from
>  "outside" the process, like the shell.
>

Identifying a thread from the outside world is _exactly_ my intent
here, so pthread_self won't do.

I can easily write a wrapper to gettid() and use it. It would make the
kvm specific patch not-necessary, which is good.

The reason I used getpid in the first place, is that all raw qemu cpus
are in the same process anyway.

It's up to you, guys.

-- 
Glauber Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."