RFR: 8247532, 8248135: Records deserialization is slow + Build microbenchmarks with --enable-preview

Chris Hegarty chris.hegarty at oracle.com
Wed Jun 24 08:20:08 UTC 2020

> On 24 Jun 2020, at 07:03, David Holmes <david.holmes at oracle.com> wrote:
> Hi Chris,
> On 24/06/2020 2:30 am, Chris Hegarty wrote:
>>> On 23 Jun 2020, at 14:49, Peter Levart <peter.levart at gmail.com> wrote:
>>> ...
>>> Ok, I'm going to push this to jdk15.
>> Thank you Peter. This is a really nice change.
>> As a follow on, and not for JDK 15, I observe that Class::isRecord0 / JVM_IsRecord shows up as consuming a significant amount of time, more than 10%, in some runs of the deserialization benchmark. The isRecord implementation is a native method in the JVM, so relatively expensive to call.
>> This shows an opportunity to improve the Class::isRecord implementation with a simple cache of the record-ness of the j.l.Class, as is done selectively with other particular aspects of a class’s state. There are various ways to implement this, but here is just one [*].
> There has been reluctance to add more and more fields to Class to cache all these new attributes that are being added

Yeah, that seems reasonable. The extra bloat should be given due consideration.

I’ve not yet counted how many of these isThis and isThat methods that there are, but I suspect that there are enough that could warrant their state being encoded into a single int or long value on j.l.Class (that could be set lazily by the VM). This would setup a convenient and reasonably efficient location to add future pieces of cached state, like isSealed.

> - but ultimately that is a call for core-libs folk to make. The general expectation is/was that the need to ask a class if it is a Record (or isSealed etc) would be rare. But (de)serialization is the exception for isRecord() as unlike enums a simple instanceof test can't be used.

It is relatively inexpensive to ask a non-record class if it is a record, but the converse is not the case.

Java Serialization can probably “workaround” this, since it already has a level of local-class cache state, so we can leverage that [*], which is probably the right thing to do for Java Serialization anyway, but I still think that there is a general tractable problem here.


diff -r 3a9521647349 src/java.base/share/classes/java/io/ObjectInputStream.java
--- a/src/java.base/share/classes/java/io/ObjectInputStream.java	Tue Jun 23 10:46:39 2020 +0100
+++ b/src/java.base/share/classes/java/io/ObjectInputStream.java	Wed Jun 24 09:07:07 2020 +0100
@@ -2182,7 +2182,7 @@
             handles.markException(passHandle, resolveEx);
-        final boolean isRecord = cl != null && isRecord(cl);
+        final boolean isRecord = desc.isRecord();
         if (isRecord) {
             assert obj == null;
             obj = readRecord(desc);

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