RFR: 8274322: Problems with oopDesc construction [v2]

[Kim Barrett]

> Please review this change to the default constructor for markWord and
> associated "change" to construction of oopDesc.
> 
> The current code never invokes the constructor for oopDesc or any of its
> derived classes.  For that to be permissible according to the Standard,
> those classes must be trivially default constructible.  And for that to be
> the case, the markWord default constructor must be trivial.
> 
> This change consists of three parts.
> 
> (1) The markWord default constructor is changed to be trivial, so the
> default constructors for oopDesc and classes derived from it will also be
> trivial. It wasn't previously trivial because the mechanism for making it so
> (a default definition) is a C++11 feature that wasn't yet supported when the
> previous constructor was defined.
> 
> (2) This change also adds static asserts to verify the relevant classes have
> trivial default constructors, to prevent later changes from unintentionally
> breaking this.
> 
> (3) This change also makes oopDesc noncopyable, to prevent inadvertent usage
> of these operations that don't make any sense.
> 
> A different approach would be to always use placement new with an
> appropriate constructor to perform the initialization, perhaps encapsulated
> in factory functions.  I did some exploration in that direction. It's a much
> larger and more complex change, though the final behavior (use constructors
> for initialization) is simpler.
> 
> Testing:
> tier1

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  dholmes review

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5729/files
  - new: https://git.openjdk.java.net/jdk/pull/5729/files/3f4cc094..5197b2c6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5729&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5729&range=00-01

  Stats: 5 lines in 1 file changed: 1 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5729.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5729/head:pull/5729

PR: https://git.openjdk.java.net/jdk/pull/5729