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Re: [Qemu-devel] [PATCH] use a thread id variable
From: |
Glauber Costa |
Subject: |
Re: [Qemu-devel] [PATCH] use a thread id variable |
Date: |
Mon, 17 Mar 2008 14:55:03 -0300 |
On Sun, Mar 9, 2008 at 11:52 AM, Gilad Ben-Yossef <address@hidden> 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."
[Qemu-devel] Re: [PATCH 0/3] Expose thread id through info cpus, Glauber Costa, 2008/03/05
[Qemu-devel] Re: [PATCH 0/3] Expose thread id through info cpus, Avi Kivity, 2008/03/06