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Implementation of memory ordering for volatile/unsafe accesses. This supports ordering of "Independent Reads of Independent Writes" as tested by VolatileIRIWTest of the torture test suite:

Example: volatile x=0, y=0

| Thread 0 | | Thread 1 | | Thread 2 | | Thread 3 |

write(x=1) read(x) write(y=1) read(y) read(y) read(x)

Disallowed: x=1, y=0 y=1, x=0

Solution: This example requires multiple-copy-atomicity. This is only assured by the sync instruction and if it is executed in the thread doing the load. Thus we implement volatile read as sync-load-acquire and omit the sync/MemBarVolatile after the volatile store. MemBarVolatile is implemented by sync on PPC.

This addresses a similar issue as fix "8012144: multiple SIGSEGVs fails on staxf" for taskqueue.hpp.

Further this change contains a fix that assures that volatile fields written in constructors are visible before the reference gets published.

Looking at the code, we found a MemBarRelease that to us, seems too strong. We think in parse1.cpp do_exits() a MemBarStoreStore should suffice.