RFR: 7102541: Implement os::set_native_thread_name() on Windows and Linux

[David Holmes]

Hi Thomas,

Based on the bug report Gerard's work stalled because of solaris issues. 
We've covered a lot of ground regarding this in the past. Personally I'm 
unhappy about a few things - the windows situations seem not that 
useful; the linux 15 character limit also renders this useless for many 
cases. Then there is the issue of whether this can only be applied by 
the current thread to itself, or by any thread to any thread.

I concede there is some value in some cases but there are enough warts 
on this to make me cringe about putting it in. (As I cringed with the 
original OSX version.)

That's not to say I'm going to oppose it, but I certainly don't champion 
it. :)

Cheers,
David

On 10/10/2014 6:38 PM, Thomas Stüfe wrote:
> Hi all,
>
> I'd like to contribute implementations for os::set_native_thread_name() on
> Windows and Linux. We have added this feature to the SAP JVM and it has
> been useful for debugging.
>
> http://cr.openjdk.java.net/~simonis/webrevs/7102541/
>
> Associated request:
> https://bugs.openjdk.java.net/browse/JDK-7102541
>
> On Windows, it uses the method described here:
> http://msdn.microsoft.com/en-us/library/xcb2z8hs.aspx
> On Linux, it uses pthread_setname_np(2).
>
> Notes for the windows implementation:
>   - os::set_native_thread_name() only has any effect if there is a debugger
> attached to the process at the time of the function call. The reason is
> that the debugger must observe the raised exception. This means that this
> method works fine if the VM is being debugged right from the start; for
> cases where the debugger attaches during VM life, threads started before
> the attach will show default names.
>   - This was tested using Visual Studio 2013 and Windbg.
>
>
> Notes for the Linux implementation:
>   - pthread_setname_np(2) needs glibc 2.12 or newer. The change loads the
> function dynamically.
>   - Thread names are truncated to 15 characters.
>   - We can see the thread names with ps (eg " ps H -p 1234 -o 'pid tid comm'
> ") or with gdb >= 4.7
>
>
> Note that not all threads show names. os::set_native_thread_name() was only
> called for JavaThread* children before this change, this change adds the VM
> thread, but there are some threads for which this function is not yet
> called; they appear with their default names.
>
> ---
>
> Note that when I was doing this change, I worked first on
> https://bugs.openjdk.java.net/browse/JDK-8060033, so I was not aware that
> Gerard Ziemski had done a lot of the same work before. But it looks like
> his changes did not appear in the hotspot? Either that or I looked at the
> wrong place... Anyway, I hope either his or my changes make it into the
> hotspot, because the feature is quite useful.
>
> Kind Regards,
>
> Thomas
>