Thanks for the comments.
Here's version 3 of the JDK and VM changes for sealed classes.
full webrev:
http://cr.openjdk.java.net/~hseigel/sealedClasses.8225056.3/webrev/
The new webrev contains just the following three changes:
1. The sealed classes API's in Class.java (permittedSubclasses() and
isSealed()) were revised and, in particular, API
permittedSubclasses() no longer uses reflection.
2. An unneeded 'if' statement was removed from
JVM_GetPermittedSubclasses() (pointed out by David.)
3. VM runtime test files SealedUnnamedModuleIntfTest.java and
Permitted.java were changed to add a test case for a non-public
permitted subclass and its sealed superclass being in the same
module and package.
Additionally, two follow on RFE's will be filed. One to add additional
VM sealed classes tests and one to improve the implementations of the
sealed classes API's in Class.java.
Thanks, Harold
On 5/28/2020 8:30 PM, David Holmes wrote:
Hi Harold,
Sorry Mandy's comment raised a couple of issues ...
On 29/05/2020 7:12 am, Mandy Chung wrote:
Hi Harold,
On 5/27/20 1:35 PM, Harold Seigel wrote:
Incremental webrev:
http://cr.openjdk.java.net/~hseigel/sealedClasses.8225056.incr.2/
full webrev:
http://cr.openjdk.java.net/~hseigel/sealedClasses.8225056.2/webrev/
Class.java
4406 ReflectionData<T> rd = reflectionData();
4407 ClassDesc[] tmp = rd.permittedSubclasses;
4408 if (tmp != null) {
4409 return tmp;
4410 }
4411
4412 if (isArray() || isPrimitive()) {
4413 rd.permittedSubclasses = new ClassDesc[0];
4414 return rd.permittedSubclasses;
4415 }
This causes an array class or primitive type to create a
ReflectionData. It should first check if this is non-sealed class
and returns a constant empty array.
It can't check if this is a non-sealed class as the isSealed() check
calls the above code! But for arrays and primitives which can't be
sealed we should just do:
4412 if (isArray() || isPrimitive()) {
4413 return new ClassDesc[0];
4414 }
But this then made me realize that we need to be creating defensive
copies of the returned arrays, as happens with other APIs that use
ReflectionData.
Backing up a bit I complained that:
public boolean isSealed() {
return permittedSubclasses().length != 0;
}
is a very inefficient way to answer the question as to whether a class
is sealed, so I suggested that the result of permittedSubclasses() be
cached. Caching is not without its own issues as we are discovering,
and when you add in defensive copies this seems to be trading one
inefficiency for another. For nestmates we don't cache
getNestMembers() because we don;t think it will be called often - it
is there to complete the introspection API of Class rather than being
anticipated as used in a regular programmatic sense. I expect the same
is true for permittedSubclasses(). Do we expect isSealed() to be used
often or is it too just there for completeness? If just for
completeness then perhaps a VM query would be a better compromise on
the efficiency front? Otherwise I can accept the current
implementation of isSealed(), and a non-caching permittedClasses() for
this initial implementation of sealed classes. If efficiency turns out
to be a problem for isSealed() then we can revisit it then.
Thanks,
David
In fact, ReflectionData caches the derived names and reflected
members for performance and also they may be invalidated when the
class is redefined. It might be okay to add
ReflectionData::permittedSubclasses while `PermittedSubclasses`
attribute can't be redefined and getting this attribute is not
performance sensitive. For example, the result of `getNestMembers`
is not cached in ReflectionData. It may be better not to add it in
ReflectionData for modifiable and performance-sensitive data.
4421 tmp = new ClassDesc[subclassNames.length];
4422 int i = 0;
4423 for (String subclassName : subclassNames) {
4424 try {
4425 tmp[i++] = ClassDesc.of(subclassName.replace('/', '.'));
4426 } catch (IllegalArgumentException iae) {
4427 throw new InternalError("Invalid type in permitted subclasses
information: " + subclassName, iae);
4428 }
4429 }
Nit: rename tmp to some other name e.g. descs
I read the JVMS but it isn't clear to me that the VM will validate
the names in `PermittedSubclasses`attribute are valid class
descriptors. I see ConstantPool::is_klass_or_reference check but
can't find where it validates the name is a valid class descriptor -
can you point me there? (otherwise, maybe define it to be unspecified?)
W.r.t. the APIs. I don't want to delay this review. I see that you
renamed the method to new API style as I brought up. OTOH, I expect
more discussion is needed. Below is a recent comment from John on
this topic [1]
One comment, really for the future, regarding the shape of the Java
API here: It uses Optional and omits the "get" prefix on accessors.
This is the New Style, as opposed to the Classic Style using null
(for "empty" results) and a "get" prefix ("getComponentType") to get
a related type. We may choose to to use the New Style for new
reflection API points, and if so let's not choose N different New
Styles, but one New Style. Personally I like removing "get"; I
accept Optional instead of null; and I also suggest that arrays (if
any) be replaced by (immutable) Lists in the New Style
There are a few existing Class APIs that use the new API style:
Class<?> arrayClass();
Optional<ClassDesc> describeConstable();
String descriptorString();
This will set up a precedence of the new API style in this class.
Should this new permittedSubclasses method return a List instead of
an array? It's okay with me if you prefer to revert back to the old
API style and follow this up after integration.
4442 * Returns true if this {@linkplain Class} is sealed.
4443 *
4444 * @return returns true if this class is sealed
NIt: {@code true} instead of true - consistent with the style this
class uses (in most methods)
test/jdk/java/lang/reflect/sealed_classes/SealedClassesReflectionTest.java
Nit: s/sealed_classes/sealedClasses/
- the test directory/file naming convention use camel case or java
variable name convention.
Thanks
[1] https://github.com/openjdk/valhalla/pull/53#issuecomment-633116043
