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Re: [Qemu-devel] [PATCH 1/2] qemu-thread: always keep the posix wrapper
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] qemu-thread: always keep the posix wrapper layer |
Date: |
Tue, 10 Apr 2018 08:35:40 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
On 04/10/2018 07:49 AM, Peter Xu wrote:
> We will conditionally have a wrapper layer depending on whether the host
> has the PTHREAD_SETNAME capability. It complicates stuff. Let's just
> keep the wrapper there, meanwhile we opt out the pthread_setname_np()
> call only. The layer can be helpful in future patches to pass data from
> the parent thread to the child thread.
>
> Signed-off-by: Peter Xu <address@hidden>
> ---
> util/qemu-thread-posix.c | 33 +++++++++++++--------------------
> 1 file changed, 13 insertions(+), 20 deletions(-)
>
> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> index b789cf32e9..3ae96210d6 100644
> --- a/util/qemu-thread-posix.c
> +++ b/util/qemu-thread-posix.c
> @@ -482,7 +482,6 @@ static void __attribute__((constructor))
> qemu_thread_atexit_init(void)
> }
>
More context:
static bool name_threads;
void qemu_thread_naming(bool enable)
{
name_threads = enable;
#ifndef CONFIG_THREAD_SETNAME_BYTHREAD
/* This is a debugging option, not fatal */
if (enable) {
fprintf(stderr, "qemu: thread naming not supported on this host\n");
}
#endif
}
>
> -#ifdef CONFIG_PTHREAD_SETNAME_NP
Why are we using CONFIG_THREAD_SETNAME_BYTHREAD in one place, and
CONFIG_PTHREAD_SETNAME_NP in another?
/me checks configure - oh:
# Hold two types of flag:
# CONFIG_THREAD_SETNAME_BYTHREAD - we've got a way of setting the name on
# a thread we have a handle to
# CONFIG_PTHREAD_SETNAME_NP - A way of doing it on a particular
# platform
even though, right now, we only either set both flags at once or leave
both clear, since we don't (yet?) have any other platform-specific ways
to do it.
> typedef struct {
> void *(*start_routine)(void *);
> void *arg;
> @@ -498,13 +497,15 @@ static void *qemu_thread_start(void *args)
> /* Attempt to set the threads name; note that this is for debug, so
> * we're not going to fail if we can't set it.
> */
> - pthread_setname_np(pthread_self(), qemu_thread_args->name);
> +#ifdef CONFIG_PTHREAD_SETNAME_NP
> + if (qemu_thread_args->name) {
> + pthread_setname_np(pthread_self(), qemu_thread_args->name);
Post-patch, this (attempts to) set the thread name if a non-NULL name is
present...
>
> -#ifdef CONFIG_PTHREAD_SETNAME_NP
> - if (name_threads) {
> - QemuThreadArgs *qemu_thread_args;
> - qemu_thread_args = g_new0(QemuThreadArgs, 1);
> - qemu_thread_args->name = g_strdup(name);
...but pre-patch, qemu_thread_args->name was left NULL unless
name_threads was true, because someone had called
qemu_thread_naming(true)...
> - qemu_thread_args->start_routine = start_routine;
> - qemu_thread_args->arg = arg;
> -
> - err = pthread_create(&thread->thread, &attr,
> - qemu_thread_start, qemu_thread_args);
> - } else
> -#endif
> - {
> - err = pthread_create(&thread->thread, &attr,
> - start_routine, arg);
> - }
> + qemu_thread_args = g_new0(QemuThreadArgs, 1);
> + qemu_thread_args->name = g_strdup(name);
...so you have changed semantics - you are now unconditionally trying to
set the thread name, instead of honoring qemu_thread_naming(). Do we
still need qemu_thread_naming() (tied to opt debug-threads)?
You need to either fix your code to remain conditional on whether
name_threads is set, or document the semantic change as intentional in
the commit message.
However, the idea for refactoring to always use the shim makes sense.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-devel] [PATCH 0/2] qemu-thread: allow cur_mon be per thread, Peter Xu, 2018/04/10
- [Qemu-devel] [PATCH 1/2] qemu-thread: always keep the posix wrapper layer, Peter Xu, 2018/04/10
- Re: [Qemu-devel] [PATCH 1/2] qemu-thread: always keep the posix wrapper layer,
Eric Blake <=
- [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Peter Xu, 2018/04/10
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Eric Blake, 2018/04/10
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Stefan Hajnoczi, 2018/04/10
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Peter Xu, 2018/04/10
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Paolo Bonzini, 2018/04/11
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Peter Xu, 2018/04/11
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Paolo Bonzini, 2018/04/11
- Re: [Qemu-devel] [PATCH 2/2] qemu-thread: let cur_mon be per-thread, Peter Xu, 2018/04/11