Hi Peter,
I for one think this looks like a very nice cleanup.
The patch drops 5 classes from a minimal VM startup test, which is a
welcome improvement.
/Claes
On 2016-05-16 00:08, Peter Levart wrote:
Hi Roger and others,
When the new Cleaner API was created the implementation of
Cleanable(s) was split into the low-level abstract
[Soft|Weak|Phantom]Cleanable classes to be used internally for
purposes where the footprint matters and their corresponding
CleanerImpl.[Soft|Weak|Phantom]CleanableRef subclasses used as
implementations that take a Runnable cleanup action and are exposed
via the public Cleaner API.
When thinking of possible JDK internal use cases for the low-level
API, I came to the conclusion that [Soft|Weak|Phantom]Cleanable
classes are not suitable as is, because in cases where footprint
matters, it is usually also the case that the number of
[Soft|Weak|Phantom]Cleanable instances created is larger and that
construction performance also matters. Especially multi-threaded
construction. I'm thinking of the use cases of auto-cleanable
concurrent data structures. In such use cases, the present features of
[Soft|Weak|Phantom]Cleanable classes, namely the guaranteed just-once
cleanup action invocation and keeping the Cleanable instance reachable
until the cleanup action is performed, are actually not needed and
just present footprint and performance (contention) overhead. They
also present an overhead as they don't allow GC to automatically
collect the Cleanable instances if the data structure containing them
becomes unreachable and corresponding registered cleanup actions
obsolete.
The mentioned features are important for public Cleaner.Cleanable
instances as they are usually used for cleanup of native resources
where the performance of their creation is not so drastically
important and where there is no intrinsic data structure to hold them
reachable.
I propose to move those features from the [Soft|Weak|Phantom]Cleanable
classes down the hierarchy to the
CleanerImpl.[Soft|Weak|Phantom]CleanableRef subclasses:
http://cr.openjdk.java.net/~plevart/jdk9-dev/Cleaner.cleanup/webrev.01/
In this change I also removed the CleanerImpl.[Soft|Weak]CleanableRef
subclasses as they are not needed and I believe will never be. I also
renamed the CleanerImpl.PhantomCleanableRef subclass to
CleanerImpl.PhantomCleanableImpl.
Changes to the implementation are straightforward. The most work was
put into the corresponding test. I did some clean-up to it and also
changed it to accommodate for the new behavior of
[Soft|Weak|Phantom]Cleanable classes. The changes speak for itself.
One of the not-so obvious changes was to replace the
CleanableCase.clearRef() action with the
CleanableCase.releaseReferent() action. The old clearRef() action did
not serve any purpose. Whether this method was called or not, the
behavior of the corresponding Cleanable was unchanged as the Reference
instance (referenced from the 'ref' field) was always of the same
strength as the Cleanable itself. So clearing it could not affect the
behavior of the Cleanable.
I changed 'ref' to hold a direct reference to the referent and renamed
the field to 'referent'. I changed the EV_XXX int constants to Event
enum constants with helper methods used in
CleanableCase.expectedCleanups() method that now returns the number of
expected cleanup invocations - in the PhantomCleanableImpl case this
is the number of expected cleanup action invocations while in the
plain XxxCleanable subclass cases it is the number of
Cleanable.clean() method invocations. I added the no-actions case to
both PhantomCleanableImpl and XxxCleanable cases and extended the
number and combinations of XxxCleanable cases.
The checkCleaned() method was extended to verify that the number of
cleanup invocations is *no more* and no less then the expected.
See how WeakKey test is now simplified. This is the typical use-case
for WeakCleanable I was talking about.
So, what do you think of this cleanup?
Regards, Peter
