http://cr.openjdk.java.net/~dholmes/8231289/webrev/src/hotspot/share/prims/jvmtiEnv.cpp.frames.html
I think it's odd that PROPER_TRANSITIONS looked like the right thing to
do, but we always took the alternate path with the large comment about
why it is evil. Can we have an RFE to move this special transition to
interfaceSupport.inline.hpp as a supported transition, so it is with the
other ones? So we don't miss it if we changed more things in the
transitions. Should this transition check for NoSafepointVerifier, for
example?
http://cr.openjdk.java.net/~dholmes/8231289/webrev/src/hotspot/share/runtime/objectMonitor.hpp.frames.html
39 // ParkEvent instead. Beware, however, that the JVMTI code
40 // knows about ObjectWaiters, so we'll have to reconcile that code.
41 // See next_waiter(), first_waiter(), etc.
Comment should be removed.
http://cr.openjdk.java.net/~dholmes/8231289/webrev/src/hotspot/share/prims/jvmtiRawMonitor.cpp.frames.html
148 void JvmtiRawMonitor::SimpleExit (Thread * Self) {
128 QNode Node (Self) ;
153 QNode * w ;
162 guarantee (w ->TState == QNode::TS_ENTER, "invariant") ;
Can you fix the style problems in the lines you changed, like these?
Fixing the style in _changed_ code doesn't distract from the code review
(having the old style does!)
This looks like a nice cleanup, and does not appear to change the what
the code does, but someone who understands the locking code should also
review it.
Thanks,
Coleen
On 9/30/19 6:52 PM, David Holmes wrote:
ping!
Thanks,
David
On 24/09/2019 3:09 pm, David Holmes wrote:
Bug: https://bugs.openjdk.java.net/browse/JDK-8231289
webrev: http://cr.openjdk.java.net/~dholmes/8231289/webrev/
The earlier attempt to rewrite JvmtiRawMonitor as a simple wrapper
around PlatformMonitor proved not so simple and ultimately had too
many issues due to the need to support Thread.interrupt.
I'd previously stated in the bug report:
"In the worst-case I suppose we could just copy ObjectMonitor to a
new class and have JvmtiRawMonitor continue to extend that (with some
additional minor adjustments) - or even just inline it all as needed."
but hadn't looked at it in detail. Richard Reingruber did look at it
and pointed out that it is actually quite simple - we barely use any
actual code from ObjectMonitor, mainly just the state. So thanks
Richard! :)
So this change basically copies or moves anything needed by
JvmtiRawMonitor from ObjectMonitor, breaking the connection between
the two. We also copy and simplify ObjectWaiter, turning it into a
QNode internal class. There is then a lot of cleanup that was applied
(and a lot more that could still be done):
- Removed the never implemented/used PROPER_TRANSITIONS ifdefs
- Fixed the disconnect between the types of non-JavaThreads expected
by the upper layer code and lower layer code
- cleaned up and simplified return codes
- consolidated code that is identical for JavaThreads and
non-JavaThreads (e.g. notify/notifyAll).
- removed used of TRAPS/THREAD where not appropriate and replaced
with "Thread * Self" in the style of the rest of the code
- changed recursions to be int rather than intptr_t (a "fixme" in the
ObjectMonitor code)
I have not changed the many style flaws with this code:
- Capitalized names
- extra spaces before ;
- ...
but could do so if needed. I wanted to try and keep it more obvious
that the fundamental functional code is actually unmodified.
There is one aspect that requires further explanation: the notion of
current pending monitor. The "current pending monitor" is stored in
the Thread and used by a number of introspection APIs for things like
finding monitors, doing deadlock detection, etc. The JvmtiRawMonitor
code would also set/clear itself as "current pending monitor". Most
uses of the current pending monitor actually, explicitly or
implicitly, ignore the case when the monitor is a JvmtiRawMonitor
(observed by the fact the mon->object() query returns NULL). The
exception to that is deadlock detection where raw monitors are at
least partially accounted for. To preserve that I added the notion of
"current pending raw monitor" and updated the deadlock detection code
to use that.
The test:
test/hotspot/jtreg/vmTestbase/nsk/jvmti/RawMonitorWait/rawmnwait005/rawmnwait005.cpp
was updated because I'd noticed previously that it was the only test
that used interrupt with raw monitors, but was in fact broken: the
test thread is a daemon thread so the main thread could terminate the
VM immediately after the interrupt() call, thus you would never know
if the interruption actually worked as expected.
Testing:
- tiers 1 - 3
- vmTestbase/nsk/monitoring/ (for deadlock detection**)
- vmTestbase/nsk/jdwp
- vmTestbase/nsk/jdb/
- vmTestbase/nsk/jdi/
- vmTestbase/nsk/jvmti/
- serviceability/jvmti/
- serviceability/jdwp
- JDK: java/lang/management
** There are no existing deadlock related tests involving
JvmtiRawMonitor. It would be interesting/useful to add them to the
existing nsk/monitoring tests that cover synchronized and JNI
locking. But it's a non-trivial enhancement that I don't really have
time to do.
Thanks,
David
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