Hi Yasumasa,
Okay, thanks.
Then I'm okay to keep the GetSingleStackTraceClosure.
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.04/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libGetThreadListStackTraces.c.html
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.04/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.c.html
I'm not sure the function 'is_same_thread() is needed.
Why do not use the JNI IsSameObject instead?
It seems to be a typo at L132 and L137.
You, probably. did not want to print the same information
for stack_info_1[i].frame_buffer[j].XXX twice.
The code at lines 112-142 is not readable.
I'd suggest to make a couple of refactoring steps.
First step to simplify this a little bit would be with
some renaming and getting rid of indexes:
71 char err_msg[EXCEPTION_MSG_LEN] = {0};
...
112 /* Iterate all jvmtiStackInfo to check */
113 for (i = 0; i < num_threads, *exception_msg !=
'\0'; i++) {
jvmtiStackInfo *si1 = stack_info_1[i];
jvmtiStackInfo *si2 = stack_info_2[i];
114 if (!IsSameObject(env, si1.thread, si2.thread))
{ /* jvmtiStackInfo::thread */
115 snprintf(err_msg, sizeof(err_msg),
116 "thread[%d] is different:
stack_info_1 = %p, stack_info_2 = %p",
117 i, sinfo1.thread, sinfo2.thread);
118 } else if (si1.state != si2.state) { /*
jvmtiStackInfo::state */
119 snprintf(err_msg, sizeof(err_msg),
120 "state[%d] is different:
stack_info_1 = %d, stack_info_2 = %d",
121 i, si1.state, si2.state);
122 } else if (si1.frame_count != si2.frame_count)
{ /* jvmtiStackInfo::frame_count */
123 snprintf(err_msg, sizeof(err_msg),
124 "frame_count[%d] is different:
stack_info_1 = %d, stack_info_2 = %d",
125 i, si1.frame_count, si2.frame_count);
126 } else {
127 /* Iterate all jvmtiFrameInfo to check */
128 for (j = 0; j < si1.frame_count; j++) {
129 if (si1.frame_buffer[j].method !=
si1.frame_buffer[j].method) { /* jvmtiFrameInfo::method */
130 snprintf(err_msg, sizeof(err_msg),
131 "thread [%d]
frame_buffer[%d].method is different: stack_info_1 = %lx,
stack_info_2 = %lx",
132 i, j,
si1.frame_buffer[j].method, si2.frame_buffer[j].method);
133 break;
134 } else if (si1.frame_buffer[j].location !=
si1.frame_buffer[j].location) { /*
jvmtiFrameInfo::location */
135 snprintf(err_msg, sizeof(err_msg),
136 "thread [%d]
frame_buffer[%d].location is different: stack_info_1 =
%ld, stack_info_2 = %ld",
137 i, j,
si1.frame_buffer[j].location, si2.frame_buffer[j].location);
138 break;
139 }
140 }
141 }
142 }
Another step would be to create functions that implement
a body of each loop.
You can use the same techniques to simplify similar place
(L127-L138) in the libOneGetThreadListStackTraces.c.
Thanks,
Serguei
On 7/3/20 15:55, Yasumasa Suenaga wrote:
Hi Serguei,
I'm not an Oracle employee, so I cannot know real
request(s) from your customers.
However JDK-8201641 says Dynatrace has requested this
enhancement.
BTW I haven't heared any request from my customers about
this.
Thanks,
Yasumasa
On 2020/07/04 4:32, serguei.spit...@oracle.com wrote:
Hi Yasumasa,
This difference is not that big to care about.
I feel this is really rare case and so, does not worth
these complications.
Do we have a real request from customers to optimize it?
Thanks,
Serguei
On 7/3/20 01:16, Yasumasa Suenaga wrote:
Hi Serguei,
Generally I agree with you, but I have concern about
the difference of the result of GetStackTrace() and
GetThreadListStackTraces().
GetStackTrace: jvmtiFrameInfo
GetThreadListStackTraces: jvmtiStackInfo
jvmtiStackInfo contains thread state, and it is
ensured it is the state of the call stack.
If we want to get both call stack and thread state, we
need to suspend target thread, and call both
GetStackTrace() and GetThreadState(). Is it ok?
I was wondering if JDK-8201641 (parent ticket of this
change) needed them for profiling (dynatrace?)
If it is responsibility of JVMTI agent implementor, I
remove this closure.
Thanks,
Yasumasa
On 2020/07/03 16:45, serguei.spit...@oracle.com wrote:
Hi Yasumasa,
After some thinking I've concluded that I do not like
this optimization
of the GetThreadListStackTraces with
GetSingleStackTraceClosure.
We may need more opinions on this but these are my
points:
- it adds some complexity and ugliness
- a win is doubtful because it has to be a rare
case, so that total overhead should not be high
- if it is really high for some use cases then it
is up to the user
to optimize it with using GetStackTrace instead
In such cases with doubtful overhead I usually prefer
the simplicity.
Good examples where it makes sense to optimize are
checks for target thread to be current thread.
In such cases there is no need to suspend the target
thread, or use a VMop/HandshakeClosure.
For instance, please, see the Monitor functions with
the check: (java_thread == calling_thread).
Getting information for current thread is frequently
used case, e.g. to get info at an event point.
Thanks,
Serguei
On 7/2/20 23:29, Yasumasa Suenaga wrote:
Hi Dan, David,
I uploaded new webrev. Could you review again?
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.04/
OneGetThreadListStackTraces.java in this webrev
would wait until thread state is transited to
"waiting" with spin wait.
CountDownLatch::await call as Dan pointed is fixed
in it :)
Diff from webrev.03:
http://hg.openjdk.java.net/jdk/submit/rev/c9aeb7001e50
Thanks,
Yasumasa
On 2020/07/03 14:15, David Holmes wrote:
On 3/07/2020 2:27 pm, Yasumasa Suenaga wrote:
On 2020/07/03 12:24, Daniel D. Daugherty wrote:
On 7/2/20 10:50 PM, David Holmes wrote:
Sorry I'm responding here without seeing latest
webrev but there is enough context I think ...
On 3/07/2020 9:14 am, Yasumasa Suenaga wrote:
Hi Dan,
Thanks for your comment!
On 2020/07/03 7:16, Daniel D. Daugherty wrote:
On 7/2/20 5:19 AM, Yasumasa Suenaga wrote:
Hi David,
I upload new webrev. Could you review again?
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.03/
src/hotspot/share/prims/jvmtiEnv.cpp
L1542: // Get stack trace with handshake
nit - please add a period at the end.
I will fix it.
L1591: *stack_info_ptr = op.stack_info();
The return parameter should not be
touched unless the return
code in 'err' == JVMTI_ERROR_NONE.
old L1582: if (err == JVMTI_ERROR_NONE) {
Please restore this check. The return
parameter should not
be touched unless the return code in
'err' == JVMTI_ERROR_NONE.
I will fix it.
But op.stack_info() will return NULL if the
error is not JVMTI_ERROR_NONE. Are you (Dan)
concerned about someone passing in a
non-null/initialized out-pointer that will be
reset to NULL if there was an error?
Actually the way we used to test this in POSIX
tests is to call
an API with known bad parameters and the return
parameter ptr
set to NULL. If the return parameter ptr was
touched when an
error should have been detected on an earlier
parameter, then
the test failed.
L1272: if (!jt->is_exiting() && (thread_oop
!= NULL)) {
nit - extra parens around the second
expression.
I will fix it.
src/hotspot/share/prims/jvmtiEnvBase.cpp
old L1532: _result =
JVMTI_ERROR_THREAD_NOT_ALIVE;
This deletion of the _result field
threw me for a minute and then
I figured out that the field is init
to JVMTI_ERROR_THREAD_NOT_ALIVE
in the constructor.
L1553: if (!jt->is_exiting() &&
(jt->threadObj() != NULL)) {
nit - extra parens around the second
expression.
I will fix it.
src/hotspot/share/prims/jvmtiEnvBase.hpp
No comments.
src/hotspot/share/runtime/vmOperations.hpp
No comments.
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/GetThreadListStackTraces.java
No comments.
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/OneGetThreadListStackTraces.java
L64: startSignal.countDown();
I was expecting this to be a call to
await() instead of
countDown(). What am I missing here?
I think this test might be passing by
accident right now, but...
Main thread (which call JVMTI functions to
test) should wait until test thread is ready.
So main thread would wait startSignal, and test
thread would count down.
No!
The test thread that previously called
obj.wait() now calls latch.await().
The main thread that previously called
obj.notify() now calls latch.countDown().
The main thread continues to spin until it sees
the target is WAITING before proceeding with the
test.
If I add spin wait to wait until transit target
thread state is WAITING (as following), we don't
need to call SuspendThread().
Which is better?
The original spin-wait loop checking for WAITING
is better because it is the only guarantee that the
target thread is blocked where you need it to be.
suspending the thread is racy as you don't know
exactly where the suspend will hit.
Thanks,
David
-----
```
/* Wait until the thread state transits to
"waiting" */
while (th.getState() != Thread.State.WAITING) {
Thread.onSpinWait();
}
```
For simplify, spin wait is prefer to
OneGetThreadListStackTraces.java in webrev.03.
Thanks,
Yasumasa
Here's the flow as I see it:
main thread
- start worker thread
- startSignal.await()
- main is now blocked
worker thread
- startSignal.countDown()
- main is now unblocked
- stopSignal.await()
- worker is now blocked
main thread
- checkCallStacks(th)
- stopSignal.countDown()
- worker is now unblocked
- th.join
- main is now blocked
worker thread
- runs off the end of run()
- main is now unblocked
main thread
- run off the end of main()
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libGetThreadListStackTraces.c
L92: jthreads = (jthread
*)malloc(sizeof(jthread) * num_threads);
You don't check for malloc() failure.
'jthreads' is allocated but never freed.
I will fix it.
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.c
L91: result =
(*jvmti)->SuspendThread(jvmti, thread);
Why are you suspending the thread?
GetAllStackTraces() and
GetThreadListStackTraces() do not require the
target thread(s)
to be suspend.
If you decide not to SuspendThread,
then you don't need the
AddCapabilities or the ResumeThread calls.
Test thread might not be entered following code
(stopSignal.await()). We might see deferent
call stack between GetAllStackTraces() and
GetThreadListStackTraces(). We cannot control
to freeze call stack of test thread in Java code.
(I didn't use SuspendThread() at first, but I
saw some errors which causes in above.)
So we need to call SuspendThread() to ensure we
can see same call stack.
If you are checking that the thread is in state
WAITING then it cannot escape from that state
and you can sample the stack multiple times from
any API and get the same result.
I suspect the errors you saw were from the
apparent incorrect use of the CountDownLatch.
With the flow outlined above, the worker thread
should be
nicely blocked in stopSignal.await() when stuff
is sampled.
Dan
Cheers,
David
-----
Thanks,
Yasumasa
Dan
On 2020/07/02 15:05, David Holmes wrote:
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().
Fixed.
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.
They would be tested in
vmTestbase/nsk/jvmti/GetStackTrace/getstacktr001/
(own call stacks), and getstacktr003 (call
stacks in other thread).
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
I updated testcases to check JNI and JVMTI
function calls.
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.
Fixed.
Thanks,
Yasumasa
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
