WeakReference with null referent
mandy.chung at oracle.com
Tue Jul 10 23:26:48 UTC 2018
On 7/10/18 4:04 PM, Éamonn McManus wrote:
>> Do you know any other example?
> Here's an example from the JDK itself:
I also found a few other similar usages in JDK to initialize
with an "empty" WeakReference field that may be updated with
a weak ref with a referent at runtime so that the code can
always assume this field is non-null.
Due to the current usage and compatibility risk, not worth
to enforce non-null referent.
> On Tue, 10 Jul 2018 at 10:11, mandy chung <mandy.chung at oracle.com> wrote:
>> On 7/9/18 11:59 PM, Peter Levart wrote:
>>> There are situations where being able to create a XxxReference without a
>>> referent is useful. For example, imagine a doubly-linked list of
>>> WeakReference subclasses - a special instance without a referent can be
>>> used as the head of such list that never goes away and simplifies
>>> insertion/deletion logic, etc...
>>> JDK's java.lang.ref.Cleaner API uses such scheme in its implementation
>>> (see jdk.internal.ref.CleanerImpl.[Phantom|Weak|Soft]CleanableRef no-arg
>> Thanks for pointing this out. It's used as a convenience and it's
>> not hard to handle insertion/deletion logic though. Another
>> alternative may be to create an object as the strongly reachable
>> referent. I wonder if any existing code depends on null referent
>> like the cleaner case and the compatibility risk. Do you know
>> any other example?
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