linux, os::current_thread_id() vs os::Linux::gettid()

[Thomas Stüfe]

Hi David,

Thank you for answering.

The reason I ask is that I work on the AIX port and would like to remove
the use of kernel thread ids.

For one, AIX kernel thread ids are 64bit, so we have a truncation error by
casting them to 32bit pid_t; also, a pthread may be scheduled to multiple
kernel threads during its lifetime by the AIX scheduler. I think the reason
we introduced kernel thread ids was because other platform ports do it too,
so I wanted to know the reason.


Thomas








On Tue, Aug 26, 2014 at 5:57 AM, David Holmes <david.holmes at oracle.com>
wrote:

> On 26/08/2014 1:46 PM, David Holmes wrote:
>
>> Hi Thomas,
>>
>> On 26/08/2014 12:55 AM, Thomas Stüfe wrote:
>>
>>> Hi,
>>>
>>> I wonder about the implementation of os::current_thread_id() on Linux.
>>>
>>> There is os::Linux::gettid() and os::current_thread_id().
>>> os::Linux::gettid() returns the kernel thread id, os::current_thread_id()
>>> returns the pthread id.
>>>
>>> os::Linux::gettid() is used to initialize OSThread::_thread_id, so that
>>> contains the kernel thread id. So now we get conflicting information from
>>> OSThread::thread_id and os::current_thread_id().
>>>
>>> As far as I see, all other platforms consistently return the kernel
>>> thread id on both code paths.
>>>
>>
>> Only AIX and BSD have gettid and both those ports were based on the
>> Linux code.
>>
>
> Sorry misunderstood your comment. Yes other platforms currently use the
> same low-level thread id for the OSThread and os::current_thread_id(). I
> suspect if you could look back in time that Solaris would have also had
> different usages eg for LWP id versus user-level thread id.
>
> David
> -----
>
>
>  Am I overlooking something or is this behaviour intentional?
>>>
>>
>> Intentional but historical, going back to old LinuxThreads. Probably one
>> of many cleanups that can be done in the linux code.
>>
>> David
>>
>>
>>> Kind Regards,
>>>
>>> ..Thomas
>>>
>>>