#2689
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Ran 28 Nov 2021 08:47AM UTC

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Files 73

Run time 6s

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Build # #2689

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push

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Committed by

ben-manes

Commit Message

Strengthen memory barriers used by benign reads and writes

`drainStatus`
The status is used to trigger the maintenance and guard against some
unnecessary runs. As the maintenance work is fast, atomic, and expected
to run frequently there is no harm even if a race causes an extra
execution. This might happen due to a buffered write to transition into
the processing state being stomped on by a cache write CAS'ing to flag
that a drain is required ASAP. This case now uses a stronger release and
opaque is used where no conflicting writes are possible.

The loop in `scheduleAfterWrite()` only assumes a read barrier if
retrying due to a failed CAS. This is guaranteed on weakly ordered
memory models like Arm's. We specifically avoided assumptions like [1]
that tried to piggyback other writes onto a CAS.

`timestamps`
The expiration timestamps are upgraded from plain loads and stores to
opaque ones. This is primarily for code clarity when matching operations
against [2]. A benefit is that it does ensure 64-bit loads on 32-bit
systems to avoid word tearing (as allowed by the Java spec, but is no
longer applicable).

[1] https://youtu.be/EFkpmFt61Jo?t=1789
[2] http://gee.cs.oswego.edu/dl/html/j9mm.html

Run Details

6372 of 6792 relevant lines covered (93.82%)

0.94 hits per line

Jobs

ID	Job ID	Ran	Files	Coverage
1	#2689.1	28 Nov 2021 08:47AM UTC	0	93.82

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