[lttng-dev] [RFC PATCH 0/2] Identify UST threads by changing thread names

[Raphaël Beamonte]

Hi!

Thanks for all of your comments, I appreciate it!
Thanks Jeremie for adding Mathieu in Cc, forgot to do it... Will
remember next time! :)

2016-06-02 9:22 GMT-04:00 Sebastien Boisvert <sboisvert at gydle.com>:
> Do you know if the name of these listener threads can be set in their constructor, directly
> when they are brought into this world ?

pthread_create does not allow to specify a name when creating the new
thread, as far as I know! That's why the 'lttng_ust_setustprocname()'
function is called first thing in the ust_listener_thread function.

> Perhaps the availability of pthread_setname_np and/or pthread_set_name_np (you have both names
> in your patch 2) should be ascertained in another venue, such as the configure.ac -- where it belongs.

True!

2016-06-03 2:24 GMT-04:00 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>:
> ----- On Jun 3, 2016, at 8:18 AM, Mathieu Desnoyers mathieu.desnoyers at efficios.com wrote:
>> lttng-ust already uses libc for mutexes and other. So I don't see why
>> you have to _add_ any explicit dependency there.
>
> and we already explicitly use pthread (pthread_create).

You're right, pthread is already used. However, when compiling the
code without adding the pthread dependency, I get the following
warning:

In file included from lttng-tracer.h:30:0,
                 from lttng-ust-abi.c:50:
compat.h: In function ‘lttng_ust_setustprocname’:
compat.h:52:2: warning: implicit declaration of function
‘pthread_setname_np’ [-Wimplicit-function-declaration]
  pthread_setname_np(pthread_self(), name);
  ^
  CC       lttng-context-procname.lo
In file included from lttng-context-procname.c:28:0:
compat.h: In function ‘lttng_ust_setustprocname’:
compat.h:52:2: warning: implicit declaration of function
‘pthread_setname_np’ [-Wimplicit-function-declaration]
  pthread_setname_np(pthread_self(), name);
  ^

It seems to be because pthread is not specified as dependency for
liblttng-ust-tracepoint in liblttng-ust/Makefile.am. However, perhaps
that pthread dependency should be added elsewhere?

>> About the glibc version, we should use autotools to detect the
>> features supported by the system libc, and pass a config define
>> to the source code, so we can use the glibc pthread_setname_np
>> if available, else we keep the current behavior.

That's a good idea, will do!

I'll update and rebase the patch following your comments.
If you have any other insight about the pthread dependency, I'm all ears!

Thanks,
Raphaël