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

[Magnus Ihse Bursie]

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.

/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