Hi Thomas,
On 2/11/2015 9:20 PM, Thomas Stüfe wrote:
Hi David,
some small changes are needed to make this build and run on AIX. I
attached a patch file with the needed additions.
Thanks!
I did not run any extensive tests on AIX, so I cannot say for sure if
this is stable. We (SAP) also may face some problems later when we port
this to HP-UX, because there, shared libraries using __thread cannot be
loaded dynamically.
Ouch!
So, I admit to some small worries, beside the issue with memory leaks on
older glibc versions. For me, this feels like something which needs
tight compiler/thread library support from the OS, so it makes us
vulnerable to running on older systems (older glibc) or building with
outdated compilers. Therefore it would be nice to have a simple way to
re-add the pthread-based TLS implementation if needed.
I can't see how to do that without keeping all the existing layers of
code - even though they would be no-ops on all the platforms that
support the compiler-based TLS. Basically just extend what I did for
Solaris to the other platforms.
Apart from that, I like the patch and think the simplification is good
and worth the effort.
Even if you can't easily add back the pthread-based TLS if needed?
It is unfortunate that hotspot may still be shackled to the past that
way - we killed off hotspot-express (in part) to remove those shackles
and allow us to modernize the codebase.
Thanks,
David
Kind Regards, Thomas
On Mon, Nov 2, 2015 at 7:40 AM, David Holmes <david.hol...@oracle.com
<mailto:david.hol...@oracle.com>> wrote:
bug: https://bugs.openjdk.java.net/browse/JDK-8132510
Open webrev: http://cr.openjdk.java.net/~dholmes/8132510/webrev.v2/
A simple (in principle) but wide-ranging change which should appeal
to our Code Deletion Engineer's. We implement Thread::current()
using a compiler/language-based thread-local variable eg:
static __thread Thread *_thr_current;
inline Thread* Thread::current() {
return _thr_current;
}
with an appropriate setter of course. By doing this we can
completely remove the platform-specific ThreadLocalStorage
implementations, and the associated os::thread_local_storage* calls,
plus all the uses of ThreadLocalStorage::thread() and
ThreadLocalStorage::get_thread_slow(). This extends the previous
work done on Solaris to implement ThreadLocalStorage::thread() using
compiler-based thread-locals.
We can also consolidate nearly all the os_cpu versions of
MacroAssembler::get_thread on x86 into one cpu specific one ( a
special variant is still needed for 32-bit Windows).
As a result of this change we have further potential cleanups:
- all the src/os/<os>/vm/thread_<os>.inline.hpp files are now
completely empty and could also be removed
- the MINIMIZE_RAM_USAGE define (which avoids use of the linux
sp-map "cache" on 32-bit) now has no affect and so could be
completely removed from the build system
I plan to do the MINIMIZE_RAM_USAGE removal as a follow up CR, but
could add the removal of the "inline" files to this CR if people
think it worth removing them.
I have one missing piece on Aarch64 - I need to change
MacroAssembler::get_thread to simply call Thread::current() as on
other platforms, but I don't know how to write that. I would
appreciate it if someone could give me the right code for that.
I would also appreciate comments/testing by the AIX and PPC64 folk
as well.
A concern about memory-leaks had previously been raised, but
experiments using simple C code on linux 86 and Solaris showed no
issues. Also note that Aarch64 already uses this kind of thread-local.
Thanks,
David
