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