Hi Ioi,
Generally seems okay.
On 22/10/2018 11:15 AM, Ioi Lam wrote:
Re-sending to the correct mailing lists. Please disregard the other email.
http://cr.openjdk.java.net/~iklam/jdk12/8212200-cds-jvmti-clfh-critical-classes.v03/
https://bugs.openjdk.java.net/browse/JDK-8212200
Hi,
CDS has various built-in assumptions that classes loaded by
SystemDictionary::resolve_well_known_classes must not be replaced
by JVMTI ClassFileLoadHook during run time, including
- field offsets computed in JavaClasses::compute_offsets
- the layout of the strings objects in the shared strings table
The "well-known" classes can be replaced by ClassFileLoadHook only
when JvmtiExport::early_class_hook_env() is true. Therefore, the
fix is to disable CDS under this condition.
I'm a little unclear why we have to iterate JvmtiEnv list when this has
to be checked during JVMTI_PHASE_PRIMORDIAL?
I have added a few test cases to try to replace shared classes,
including well-known classes and other classes. See
comments in ReplaceCriticalClasses.java for details.
As a clean up, I also renamed all use of "preloaded" in
the source code to "well-known". They refer to the same thing
in HotSpot, so there's no need to use 2 terms. Also, The word
"preloaded" is ambiguous -- it's unclear when "preloading" happens,
and could be confused with what CDS does during archive dump time.
A few specific comments:
src/hotspot/share/classfile/systemDictionary.cpp
+ bool SystemDictionary::is_well_known_klass(Symbol* class_name) {
+ for (int i = 0; ; i++) {
+ int sid = wk_init_info[i];
+ if (sid == 0) {
+ break;
+ }
I take it a zero value is a guaranteed end-of-list sentinel?
+ for (int i=FIRST_WKID; i<last; i++) {
Style nit: need spaces around = and <
---
test/hotspot/jtreg/runtime/SharedArchiveFile/serviceability/ReplaceCriticalClasses.java
New file should have current copyright year only.
31 * @comment CDS should not be disabled -- these critical classes
will be replaced because JvmtiExport::early_class_hook_env() is true.
Comment seems contradictory: if we replace critical classes then CDS
should be disabled right??
I expected to see tests that checked for:
"CDS is disabled because early JVMTI ClassFileLoadHook is in use."
in the output. ??
Thanks,
David
> In early e-mails Jiangli wrote:
>
> We should consider including more classes from the default classlist
> in the test. Archived classes loaded during both 'early' phase and after
> should be tested.
Done.
> For future optimizations, we might want to prevent loading additional
> shared classes if any of the archived system classes is changed.
What's the benefit of doing this? Today we already stop loading a shared
class if its super class was not loaded from the archive.
Thanks
- Ioi
