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
