Hi Yasumasa,
On 1/07/2020 11:53 am, Yasumasa Suenaga wrote:
Hi,
I uploaded new webrev. Could review again?
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.02/
Updates look fine - thanks.
One minor nit:
1274 _collector.allocate_and_fill_stacks(1);
1275 _collector.set_result(JVMTI_ERROR_NONE);
In the other places where you use _collector you rely on result being
initialized to JVMTI_ERROR_NONE, rather than setting it directly after
allocate_and_fill_stacks().
src/hotspot/share/prims/jvmtiEnvBase.cpp
820 assert(SafepointSynchronize::is_at_safepoint() ||
821 java_thread->is_thread_fully_suspended(false,
&debug_bits) ||
822 current_thread == java_thread->active_handshaker(),
823 "at safepoint / handshake or target thread is
suspended");
I don't think the suspension check is necessary, as even if the
target is suspended we must still be at a safepoint or in a
handshake with it. Makes me wonder if we used to allow a racy
stacktrace operation on a suspended thread, assuming it would
remain suspended?
This function (JvmtiEnvBase::get_stack_trace()) can be called to get own
stack trace. For example, we can call GetStackTrace() for current thread
at JVMTI event.
So I changed assert as below:
```
820 assert(current_thread == java_thread ||
821 SafepointSynchronize::is_at_safepoint() ||
822 current_thread == java_thread->active_handshaker(),
823 "call by myself / at safepoint / at handshake");
```
Yep good catch. I hope current tests caught that.
Speaking of tests ...
In the native code I think you need to check the success of all JNI
methods that can throw exceptions - otherwise I believe the tests may
trigger warnings if -Xcheck:jni is used with them. See for example:
test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/libHeapMonitorTest.cpp
In the Java code the target thread:
45 public void run() {
46 try {
47 synchronized (lock) {
48 lock.wait();
49 System.out.println("OK");
50 }
is potentially susceptible to spurious wakeups. Using a CountDownLatch
would be robust.
Thanks,
David
-----
Thanks,
Yasumasa
On 2020/07/01 8:48, David Holmes wrote:
Hi Yasumasa,
On 1/07/2020 9:05 am, Yasumasa Suenaga wrote:
Hi David,
1271 ResourceMark rm;
IIUC at this point the _calling_thread is the current thread, so
we can use:
ResourceMark rm(_calling_thread);
If so, we can call make_local() in L1272 without JavaThread (or we
can pass current thread to make_local()). Is it right?
```
1271 ResourceMark rm;
1272
_collector.fill_frames((jthread)JNIHandles::make_local(_calling_thread,
thread_oop),
1273 jt, thread_oop);
```
Sorry I got confused, _calling_thread may not be the current thread as
we could be executing the handshake in the target thread itself. So
the ResourceMark is correct as-is (implicitly for current thread).
The argument to fill_frames will be used in the jvmtiStackInfo and
passed back to the _calling_thread, so it must be created via
make_local(_calling_thread, ...) as you presently have.
Thanks,
David
Thanks,
Yasumasa
On 2020/07/01 7:05, David Holmes wrote:
On 1/07/2020 12:17 am, Yasumasa Suenaga wrote:
Hi David,
Thank you for reviewing! I will update new webrev tomorrow.
466 class MultipleStackTracesCollector : public StackObj {
498 class VM_GetAllStackTraces : public VM_Operation {
499 private:
500 JavaThread *_calling_thread;
501 jint _final_thread_count;
502 MultipleStackTracesCollector _collector;
You can't have a StackObj as a member of another class like that
as it may not be on the stack. I think
MultipleStackTracesCollector should not extend any allocation
class, and should always be embedded directly in another class.
I'm not sure what does mean "embedded".
Is it ok as below?
```
class MultipleStackTracesCollector {
:
}
class GetAllStackTraces : public VM_Operation {
private:
MultipleStackTracesCollector _collector;
}
```
Yes that I what I meant.
Thanks,
David
-----
Thanks,
Yasumasa
On 2020/06/30 22:22, David Holmes wrote:
Hi Yasumasa,
On 30/06/2020 10:05 am, Yasumasa Suenaga wrote:
Hi David, Serguei,
I updated webrev for 8242428. Could you review again?
This change migrate to use direct handshake for GetStackTrace()
and GetThreadListStackTraces() (when thread_count == 1).
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.01/
This looks really good now! I only have a few nits below. There is
one thing I don't like about it but it requires a change to the
main Handshake logic to address - in
JvmtiEnv::GetThreadListStackTraces you have to create a
ThreadsListHandle to convert the jthread to a JavaThread, but then
the Handshake::execute_direct creates another ThreadsListHandle
internally. That's a waste. I will discuss with Robbin and file a
RFE to have an overload of execute_direct that takes an existing
TLH. Actually it's worse than that because we have another TLH in
use at the entry point for the JVMTI functions, so I think there
may be some scope for simplifying the use of TLH instances -
future RFE.
---
src/hotspot/share/prims/jvmtiEnvBase.hpp
451 GetStackTraceClosure(JvmtiEnv *env, jint start_depth, jint
max_count,
452 jvmtiFrameInfo* frame_buffer, jint*
count_ptr)
453 : HandshakeClosure("GetStackTrace"),
454 _env(env), _start_depth(start_depth),
_max_count(max_count),
455 _frame_buffer(frame_buffer), _count_ptr(count_ptr),
456 _result(JVMTI_ERROR_THREAD_NOT_ALIVE) {
Nit: can you do one initializer per line please.
This looks wrong:
466 class MultipleStackTracesCollector : public StackObj {
498 class VM_GetAllStackTraces : public VM_Operation {
499 private:
500 JavaThread *_calling_thread;
501 jint _final_thread_count;
502 MultipleStackTracesCollector _collector;
You can't have a StackObj as a member of another class like that
as it may not be on the stack. I think
MultipleStackTracesCollector should not extend any allocation
class, and should always be embedded directly in another class.
481 MultipleStackTracesCollector(JvmtiEnv *env, jint
max_frame_count) {
482 _env = env;
483 _max_frame_count = max_frame_count;
484 _frame_count_total = 0;
485 _head = NULL;
486 _stack_info = NULL;
487 _result = JVMTI_ERROR_NONE;
488 }
As you are touching this can you change it to use an initializer
list as you did for the HandshakeClosure, and please keep one item
per line.
---
src/hotspot/share/prims/jvmtiEnvBase.cpp
820 assert(SafepointSynchronize::is_at_safepoint() ||
821 java_thread->is_thread_fully_suspended(false,
&debug_bits) ||
822 current_thread == java_thread->active_handshaker(),
823 "at safepoint / handshake or target thread is
suspended");
I don't think the suspension check is necessary, as even if the
target is suspended we must still be at a safepoint or in a
handshake with it. Makes me wonder if we used to allow a racy
stacktrace operation on a suspended thread, assuming it would
remain suspended?
1268 oop thread_oop = jt->threadObj();
1269
1270 if (!jt->is_exiting() && (jt->threadObj() != NULL)) {
You can use thread_oop in line 1270.
1272
_collector.fill_frames((jthread)JNIHandles::make_local(_calling_thread,
thread_oop),
1273 jt, thread_oop);
It is frustrating that this entire call chain started with a
jthread reference, which we converted to a JavaThread, only to
eventually need to convert it back to a jthread! I think there is
some scope for simplification here but not as part of this change.
1271 ResourceMark rm;
IIUC at this point the _calling_thread is the current thread, so
we can use:
ResourceMark rm(_calling_thread);
---
Please add @bug lines to the tests.
I'm still pondering the test logic but wanted to send this now.
Thanks,
David
-----
VM_GetThreadListStackTrace (for GetThreadListStackTraces) and
VM_GetAllStackTraces (for GetAllStackTraces) have inherited
VM_GetMultipleStackTraces VM operation which provides the feature
to generate jvmtiStackInfo. I modified VM_GetMultipleStackTraces
to a normal C++ class to share with HandshakeClosure for
GetThreadListStackTraces (GetSingleStackTraceClosure).
Also I added new testcases which test GetThreadListStackTraces()
with thread_count == 1 and with all threads.
This change has been tested in serviceability/jvmti
serviceability/jdwp vmTestbase/nsk/jvmti vmTestbase/nsk/jdi
vmTestbase/nsk/jdwp.
Thanks,
Yasumasa
On 2020/06/24 15:50, Yasumasa Suenaga wrote:
Hi all,
Please review this change:
JBS: https://bugs.openjdk.java.net/browse/JDK-8242428
webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.00/
This change replace following VM operations to direct handshake.
- VM_GetFrameCount (GetFrameCount())
- VM_GetFrameLocation (GetFrameLocation())
- VM_GetThreadListStackTraces (GetThreadListStackTrace())
- VM_GetCurrentLocation
GetThreadListStackTrace() uses direct handshake if thread count
== 1. In other case (thread count > 1), it would be performed as
VM operation (VM_GetThreadListStackTraces).
Caller of VM_GetCurrentLocation
(JvmtiEnvThreadState::reset_current_location()) might be called
at safepoint. So I added safepoint check in its caller.
This change has been tested in serviceability/jvmti
serviceability/jdwp vmTestbase/nsk/jvmti vmTestbase/nsk/jdi
vmTestbase/ns
k/jdwp.
Also I tested it on submit repo, then it has execution error
(mach5-one-ysuenaga-JDK-8242428-20200624-0054-12034717) due to
dependency error. So I think it does not occur by this change.
Thanks,
Yasumasa
