gdb show thread names

Jonny Grant jg@jguk.org
Mon Jun 15 21:28:41 GMT 2020



On 15/06/2020 22:12, Pedro Alves wrote:
> On 6/15/20 9:53 PM, Jonny Grant wrote:
>>
>>
>> On 15/06/2020 17:21, Philippe Waroquiers wrote:
>>> On Mon, 2020-06-15 at 16:51 +0100, Pedro Alves wrote:
>>>>
>>>> Starting program: /home/pedro/brno/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.threads/names/names 
>>>> [Thread debugging using libthread_db enabled]
>>>> Using host libthread_db library "/lib64/libthread_db.so.1".
>>>> [New Thread 0x7ffff74b8700 (LWP 24171) "main"]
>>>> [New Thread 0x7ffff6cb7700 (LWP 24172) "main"]
>>>> [New Thread 0x7ffff64b6700 (LWP 24173) "main"]
>>>>
>>>> Thread 1 "main" hit Breakpoint 1, all_threads_ready () at /home/pedro/gdb/binutils-gdb/src/gdb/testsuite/gdb.threads/names.c:51
>>>> 51      }
>>>> (gdb) info threads 
>>>>   Id   Target Id                                  Frame 
>>>> * 1    Thread 0x7ffff7fb5740 (LWP 24170) "main"   all_threads_ready () at /home/pedro/gdb/binutils-gdb/src/gdb/testsuite/gdb.threads/names.c:51
>>>>   2    Thread 0x7ffff74b8700 (LWP 24171) "carrot" 0x00007ffff7bc89aa in futex_wait (private=0, expected=4, futex_word=0x7fffffffd604) at ../sysdeps/unix/sysv/linux/futex-internal.h:61
>>>>   3    Thread 0x7ffff6cb7700 (LWP 24172) "potato" 0x00007ffff7bc89aa in futex_wait (private=0, expected=4, futex_word=0x7fffffffd604) at ../sysdeps/unix/sysv/linux/futex-internal.h:61
>>>>   4    Thread 0x7ffff64b6700 (LWP 24173) "celery" 0x00007ffff7bc89aa in futex_wait (private=0, expected=4, futex_word=0x7fffffffd604) at ../sysdeps/unix/sysv/linux/futex-internal.h:61
>>>> (gdb) 
>>>>
>>>> I.e., printing the thread name when the thread is created
>>>> looks more confusing than helpful to me.
>>> Yes, that is confusing.
>>>
>>> And for the following events, when I tried, the patch was far to be ready 
>>> e.g. for the exit events, it gives (for the above):
>>>   (gdb) c
>>>   Continuing.
>>>   [Thread 0x7ffff743d700 (LWP 22783) exited]
>>>   [Thread 0x7ffff7c3e700 (LWP 22782) exited]
>>>   [Thread 0x7ffff7c3f740 (LWP 22778) "main" exited]
>>>
>>> So, unclear why there is no carrot, potato or celery in the 2 exited threads
>>> but "main" is present.
>>> (and sometimes there is no names in any exited event).
>>>
>>> So, when I looked at it, it needed quite some more work ...
>>>
>>> Philippe
>>>
>>
>> Hi, Maybe it is more complicated than it is worth after all.
>> Although, I did think new threads inherited the process executable name, rather than the main() symbol.
> 
> It's not the main() symbol, it's the name of the parent thread.
> The testcase does:
> 
>   pthread_setname_np (pthread_self (), "main");
> 
> on the main thread before spawning the other threads.
> 
> So a child thread of "carrot" would be called "carrot" too by
> default, until it changed its name.
> 
> If we removed that pthread_setname_np call on the main thread, then
> the main thread's name would default to the process executable name
> indeed.
> 
> 
> If we included the thread id in these notifications instead, I think it
> would be quite useful.  Like, we could have:
> 
>  [Thread 1.2 (0x7ffff74b8700 (LWP 13984)) created]
>  [Thread 1.2 (0x7ffff74b8700 (LWP 13984)) exited]


I'm just looking at my original email, I saw present behaviour is :-

[Thread 0x7fff695e9700 (LWP 3580240) exited]
[New Thread 0x7fff98ff9700 (LWP 3580609)]

May I ask which do you refer to as the 'thread id'?
I know on the Linux kernel there is gettid syscall, but they don't correspond to the pthread_self() handle.

Jonny


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