[concurrency-interest] Is Reference.reachabilityFence() needed in Reference constructor?

Gregg Wonderly gergg at cox.net
Wed Oct 21 18:10:26 EDT 2015


> On Oct 21, 2015, at 4:44 PM, Vitaly Davidovich <vitalyd at gmail.com> wrote:
> 
> But the referent arg is on the stack (since the constructor is)
> Aren't all variables on the stack strongly reachable?
> 
> No.  The stacks are scanned and oopmaps are inspected to find live objects, which then serve as the root of a reachability graph, but mere presence of an object on the stack does not mean it's reachable for GC purposes.

That seems highly problematic for WeakReference and company to be usable.  How can any object using those APIs guarantee that the object itself is strongly reachable?  Doesn’t seem like they can.  Strong references can only ever be guaranteed by using a static reference, which makes for non-static environments to be really difficult to “develop” in.

Gregg Wonderly

> 
> On Wed, Oct 21, 2015 at 4:29 PM, thurstonn <thurston at nomagicsoftware.com <mailto:thurston at nomagicsoftware.com>> wrote:
> But the referent arg is on the stack (since the constructor is)
> Aren't all variables on the stack strongly reachable?
> 
> 
> 
> --
> View this message in context: http://jsr166-concurrency.10961.n7.nabble.com/Is-Reference-reachabilityFence-needed-in-Reference-constructor-tp12819p12824.html <http://jsr166-concurrency.10961.n7.nabble.com/Is-Reference-reachabilityFence-needed-in-Reference-constructor-tp12819p12824.html>
> Sent from the JSR166 Concurrency mailing list archive at Nabble.com.
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