(10) (M) RFR: 8174231: Factor out and share PlatformEvent and Parker code for POSIX systems

[Magnus Ihse Bursie]

On 2017-05-19 09:15, David Holmes wrote:
> Hi Magnus,
>
> On 18/05/2017 8:06 PM, Magnus Ihse Bursie wrote:
>>
>>
>> On 2017-05-18 09:35, David Holmes wrote:
>>> On 18/05/2017 5:32 PM, Magnus Ihse Bursie wrote:
>>>> On 2017-05-18 08:25, David Holmes wrote:
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8174231
>>>>>
>>>>> webrevs:
>>>>>
>>>>> Build-related: 
>>>>> http://cr.openjdk.java.net/~dholmes/8174231/webrev.top/
>>>>
>>>> Build changes look  good.
>>>
>>> Thanks Magnus! I just realized I left in the AC_MSG_NOTICE debugging 
>>> prints outs - do you want me to remove them? I suppose they may be 
>>> useful if something goes wrong on some platform.
>>
>> I didn't even notice them. :-/
>>
>> It's a bit unfortunate we don't have a debug level on the logging 
>> from configure. :-( Otherwise they would have clearly belonged there.
>>
>> The AC_MSG_NOTICE messages stands out much from the rest of the 
>> configure log, so maybe it's better that you remove them. The logic 
>> itself is very simple, if the -D flags are missing then we can surely 
>> tell what happened. So yes, please remove them.
>
> Webrev updated in place.
Code looks good!

In the future, I very much prefer if you do not update webrevs in place. 
It's hopeless if you start reading a thread after some updates have 
occured, the mails don't make any sense, and it's hard to follow 
after-the-fact how the patch evolved.

>
> I have removed them to avoid noise - particularly as they get executed 
> twice.
>
> I also made an adjustment to AC_SEARCH_LIBS as I don't want to pass 
> the saved_LIBS value in explicitly, but want it to use the LIBS value 
> - which is no longer cleared before the call. I've verified all 
> platforms are okay - except AIX which I'll need Thomas to recheck when 
> he can.
>
> I also discovered an oddity in that our ARM64 builds seem to use 
> different system libraries in that librt.so is not needed for 
> clock_gettime. This still seems to work ok. Of more of a concern if we 
> were expand this kind of function-existence check is that libc seems 
> to contain "dummy" (or at least dysfunctional) versions of a number of 
> the core pthread APIs!
That's good to know.

/Magnus
>
> Thanks,
> David
>
>> Alternatively, rewrite them as CHECKING/RESULT, if you want to keep 
>> the logging. That way they match better the rest of the configure log 
>> (and also describes what you're doing). Just check if AC_SEARCH_LIBS 
>> prints some output (likely so, I think), then you can't do it in the 
>> middle of a CHECKING/RESULT pair, but have to do the CHECKING part 
>> after AC_SEARCH_LIBS.
>>
>> /Magnus
>>
>>>
>>> David
>>>
>>>> /Magnus
>>>>
>>>>>       hotspot:
>>>>> http://cr.openjdk.java.net/~dholmes/8174231/webrev.hotspot/
>>>>>
>>>>> First a big thank you to Thomas Stuefe for testing various 
>>>>> versions of
>>>>> this on AIX.
>>>>>
>>>>> This is primarily a refactoring and cleanup exercise (ie lots of
>>>>> deleted duplicated code!).
>>>>>
>>>>> I have taken the PlatformEvent, PlatformParker and Parker::* code, 
>>>>> out
>>>>> of os_linux and moved it into os_posix for use by Linux, OSX, BSD, 
>>>>> AIX
>>>>> and perhaps one day Solaris (more on that later).
>>>>>
>>>>> The Linux code was the most functionally complete, dealing with
>>>>> correct use of CLOCK_MONOTONIC for relative timed waits, and the
>>>>> default wall-clock for absolute timed waits. That functionality is
>>>>> not, unfortunately, supported by all our POSIX platforms so there are
>>>>> some configure time build checks to set some #defines, and then some
>>>>> dynamic lookup at runtime**. We allow for the runtime environment to
>>>>> be less capable than the build environment, but not the other way
>>>>> around (without build time support we don't know the runtime types
>>>>> needed to make library calls).
>>>>>
>>>>> ** There is some duplication of dynamic lookup code on Linux but this
>>>>> can be cleaned up in future work if we refactor the time/clock code
>>>>> into os_posix as well.
>>>>>
>>>>> The cleanup covers a number of things:
>>>>> - removal of linux anachronisms that got "ported" into the other
>>>>> platforms
>>>>>   - eg EINTR can not be returned from the wait methods
>>>>> - removal of solaris anachronisms that got ported into the linux code
>>>>> and then on to other platforms
>>>>>   - eg ETIMEDOUT is what we expect never ETIME
>>>>> - removal of the ancient/obsolete os::*::allowdebug_blocked_signals()
>>>>> from the Parker methods
>>>>> - consolidation of unpackTime and compute_abstime into one utility
>>>>> function
>>>>> - use statics for things completely private to the implementation
>>>>> rather than making them part of the os* API (eg access to condAttr
>>>>> objects)
>>>>> - cleanup up commentary and style within methods of the same class
>>>>> - clean up coding style in places eg not using Names that start with
>>>>> capitals.
>>>>>
>>>>> I have not tried to cleanup every single oddity, nor tried to
>>>>> reconcile differences between the very similar in places 
>>>>> PlatformEvent
>>>>> and Park methods. For example PlatformEvent still examines the
>>>>> FilterSpuriousWakeups** flag, and Parker still ignores it.
>>>>>
>>>>> ** Perhaps a candidate for deprecation and future removal.
>>>>>
>>>>> There is one mini "enhancement" slipped in this. I now explicitly
>>>>> initialize mutexes with a mutexAttr object with its type set to
>>>>> PTHREAD_MUTEX_NORMAL, instead of relying on the definition of
>>>>> PTHREAD_MUTEX_DEFAULT. On FreesBSD the default is not "normal" but
>>>>> "error checking" and so is slow. On all other current platforms there
>>>>> is no effective change.
>>>>>
>>>>> Finally, Solaris is excluded from all this (other than the debug
>>>>> signal blocking cleanup) because it potentially supports three
>>>>> different low-level sync subsystems: UI thr*, Pthread, and direct LWP
>>>>> sync. Solaris cleanup would be a separate RFE.
>>>>>
>>>>> No doubt I've overlooked mentioning something that someone will 
>>>>> spot. :)
>>>>>
>>>>> Thanks,
>>>>> David
>>>>
>>