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

[David Holmes]

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.

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
>