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

[David Holmes]

Replying to all this time :)

On 19/05/2017 7:15 PM, Magnus Ihse Bursie wrote:
> 
> 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!

Thanks for the re-review.

> 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.

Sorry. Point taken.

David
-----


>>
>> 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
>>>>>
>>>
>