RFR(s): 8149036: Add UL tracing for thread related events at os level

David Holmes david.holmes at oracle.com
Wed Feb 24 12:17:39 UTC 2016

Hi Thomas,

Been waiting for the dust to settle :)

On 24/02/2016 7:24 PM, Thomas Stüfe wrote:
> Coleen, Marcus,
> thank you for reviewing, and @Coleen, thanks for the sponsoring offer!
> Here the latest Webrev:
> http://cr.openjdk.java.net/~stuefe/webrevs/8149036-add-tracing-for-thread-events/webrev.02/webrev/index.html
> As Marcus suggested, I added a new "thread" tag and added the tag to the
> logging calls.

I have a few comments ...


  786     LogHandle(os, thread) log;
  787     if (log.is_debug()) {

I think it is preferable to only create the LogHandle inside the if 
block. Normally we do an "if (is_enabled...())" check first.

  793         log.warning("Failed to start thread - pthread_create 
failed (%s) for attributes: %s.",
  794           strerror(errno), os::Posix::describe_pthread_attr(buf, 
sizeof(buf), &attr));

pthread_* functions don't set errno they return the error code directly.

Ditto for src/os/linux/vm/os_linux.cpp



Why did you use a different style for the thr_create logging compared to 
*NIX? The flags can be described similarly to a pthread-attr object.

Similar comment for os_windows.cpp.



Personally I think plain warning(...) calls should be converted to 
untagged logging calls - otherwise the warning will likely never be seen 
and we want these warnings to be quite visible. But the policy is to do 
what you did.

> btw, I found the command line a bit confusing:
> If a logging call is tagged with two tags A and B, I would have thought the
> default behaviour of "-Xlog:A" is to log all calls tagged at least with A,
> not all calls which are solely tagged with A and nothing else. I could not
> even think ot a use case for the latter.

The syntax/semantics is somewhat subjective and obviously have to be 
learned. I like the fact -Xlog:os only turns on things tagged only with 

> After some searching, I found that the behaviour I want and I would think
> makes sense as default is "-Xlog:A*".

-Xlog:help shows

-Xlog Usage: -Xlog[:[what][:[output][:[decorators][:output-options]]]]
          where 'what' is a combination of tags and levels on the form 
          Unless wildcard (*) is specified, only log messages tagged 
with exactly the tags specified will be matched.

> This also means that log lines will be mysteriously disappearing from
> output if someone adds another tag to that line, unless I always use an
> asterix? Or am I just slow to understand the command line syntax?

Unfortunately you need to know how the code is tagged to know what log 
output to ask for. Once we put these in place we're introducing a new 
set of compatibility constraints that will make it hard to rework the 
tagging in the future.


> Kind Regards, Thomas
> On Tue, Feb 23, 2016 at 6:52 PM, Marcus Larsson <marcus.larsson at oracle.com>
> wrote:
>> Hi,
>> On 2016-02-22 17:54, Thomas Stüfe wrote:
>>> Dear all,
>>> please take a look at this proposed addition to UL. This adds a number of
>>> trace points to thread creation. In detail:
>>> - it traces thread creation and thread creation errors, including pthread
>>> attributes (for Posix platforms)
>>> - it traces stack location and creation/removal of stack guard pages.
>>> This all was first AIX-only tracing, but I converted this to UL and made
>>> it
>>> available on all platforms.
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8149036
>>> Webrev:
>>> http://cr.openjdk.java.net/~stuefe/webrevs/8149036-add-tracing-for-thread-events/webrev.00/webrev/
>> It might be a good idea to add a 'thread' tag and use that in addition to
>> the os tag for these messages. It would allow easy filtering of these
>> messages for those interested/uninterested. Just 'os' alone is quite a wide
>> area.
>> Thanks,
>> Marcus
>> Note also that I added a helper function, os::errno_name(), which is a very
>>> simple replacement for strerror() without its problems (thread safety,
>>> unwanted localizations...).
>>> What do you think?
>>> Kind Regards, Thomas

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