Hi David,
If you don't have any other questions/comments, can I proceed to push?
Kim, thank you very much for the all explanations.
Thanks,
Sangheon
On 02/07/2017 11:00 PM, Kim Barrett wrote:
On Feb 6, 2017, at 10:44 PM, David Holmes<david.hol...@oracle.com> wrote:
Does the SATB occur at a global safepoint?
SATB is the approach G1 uses for a part of concurrent collection. It
defines the invariants that must be maintained by the mutator so that
the collector can find all the live objects. The barriers in question
are executed by the mutator concurrently with the collector, in order
to inform the collector of reachability graph modifications.
Is that a "no"? :) I don't understand how the barriers operate in relation to
concurrent actions by the GC. To take the current case, what prevents the GC from
deciding that the referent is garbage and can deleted, before the enqueue is called? I
assumed a safepoint had to be involved somewhere so that the sequence of actions:
extract, enqueue, store, was atomic with respect to the GC.
To be more precise, the barriers in question are executed by the
mutator concurrently with the marking phase of the collector. Once
marking is (mostly) complete, G1 safepoints and performs various
tasks, including reference processing. The barrier must be atomic
wrto that safepoint (which is accomplished by not allowing any
safepoints during the barrier execution). So yes, the sequence of
extract and enqueue are atomic wrto the relevant part of the GC.
