On 7/9/20 12:00 PM, Patricio Chilano wrote:
Hi Yasumasa,
On 7/9/20 9:30 AM, Yasumasa Suenaga wrote:
On 2020/07/09 17:58, David Holmes wrote:
Hi Yasumasa,
On 9/07/2020 10:25 am, Yasumasa Suenaga wrote:
Hi Dan,
Thanks for your comment!
I uploaded new webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.09/
Diff from previous webrev:
http://hg.openjdk.java.net/jdk/submit/rev/5d167adf8524
I saw similar build errors in libOneGetThreadListStackTraces.cpp on
Windows.
This webrev fixes them.
You shouldn't use %p as it may not be portable. In the VM we use
INTPTR_FORMAT and convert the arg using p2i. I don't know what
exists in the testing code.
I replaced %p to %lx, and also cast values to unsigned long [1] [2],
but the test on submit repo was failed.
Can anyone share details of
mach5-one-ysuenaga-JDK-8242428-20200709-1030-12500928 ?
These are the errors I see for the macOS build:
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp:53:14:
error: format specifies type 'long long' but the argument has type
'jlocation' (aka 'long') [-Werror,-Wformat]
fi1->location, fi2->location);
^~~~~~~~~~~~~
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp:53:29:
error: format specifies type 'long long' but the argument has type
'jlocation' (aka 'long') [-Werror,-Wformat]
fi1->location, fi2->location);
^~~~~~~~~~~~~
These are the ones I see for the Windows build:
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(48):
warning C4311: 'type cast': pointer truncation from 'jmethodID' to
'unsigned long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(48):
warning C4302: 'type cast': truncation from 'jmethodID' to 'unsigned
long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(48):
warning C4311: 'type cast': pointer truncation from 'jmethodID' to
'unsigned long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(48):
warning C4302: 'type cast': truncation from 'jmethodID' to 'unsigned
long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(70):
warning C4311: 'type cast': pointer truncation from 'jthread' to
'unsigned long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(70):
warning C4302: 'type cast': truncation from 'jthread' to 'unsigned long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(70):
warning C4311: 'type cast': pointer truncation from 'jthread' to
'unsigned long'
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp(70):
warning C4302: 'type cast': truncation from 'jthread' to 'unsigned long'
You will probably want to use the macros defined in
src/hotspot/share/utilities/globalDefinitions.hpp. Let me know if you
need me to test something.
With these changes the build works okay on Linux, Windows and macOS:
---
a/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
+++
b/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
@@ -27,4 +27,5 @@
#include <stdio.h>
#include <stdlib.h>
+#include <inttypes.h>
#define MAX_FRAMES 100
@@ -45,11 +46,11 @@
if (fi1->method != fi2->method) { /* jvmtiFrameInfo::method */
snprintf(err_msg, sizeof(err_msg),
- "method is different: fi1 = %p, fi2 = %p",
- fi1->method, fi2->method);
+ "method is different: fi1 = 0x%016" PRIxPTR " , fi2 =
0x%016" PRIxPTR,
+ (intptr_t)fi1->method, (intptr_t)fi2->method);
env->FatalError(err_msg);
} else if (fi1->location != fi2->location) { /*
jvmtiFrameInfo::location */
snprintf(err_msg, sizeof(err_msg),
- "location is different: fi1 = %lld, fi2 = %lld",
- fi1->location, fi2->location);
+ "location is different: fi1 = %" PRId64 " , fi2 = %" PRId64,
+ (int64_t)fi1->location, (int64_t)fi2->location);
env->FatalError(err_msg);
}
@@ -67,5 +68,5 @@
if (!is_same) { /* jvmtiStackInfo::thread */
snprintf(err_msg, sizeof(err_msg),
- "thread is different: si1 = %p, si2 = %p", si1->thread,
si2->thread);
+ "thread is different: si1 = 0x%016" PRIxPTR " , si2 =
0x%016" PRIxPTR, (intptr_t)si1->thread, (intptr_t)si2->thread);
env->FatalError(err_msg);
} else if (si1->state != si2->state) { /* jvmtiStackInfo::state */
Maybe you can use something like that.
Thanks,
Patricio
Thanks,
Patricio
Thanks,
Yasumasa
[1] http://hg.openjdk.java.net/jdk/submit/rev/dfca51958217
[2] http://hg.openjdk.java.net/jdk/submit/rev/3665361fa91b
David
-----
Thanks,
Yasumasa
On 2020/07/09 1:42, Daniel D. Daugherty wrote:
> http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.08/
src/hotspot/share/prims/jvmtiEnv.cpp
No comments.
src/hotspot/share/prims/jvmtiEnvBase.cpp
L1159: Thread *current_thread = Thread::current();
Please add "#ifdef ASSERT" above and "#endif" below since
current_thread is only used for the assert() in this
function.
src/hotspot/share/prims/jvmtiEnvBase.hpp
L549: jthread java_thread, jint
max_frame_count)
L552: _jthread(java_thread),
Please: s/java_thread/thread/ on both lines.
src/hotspot/share/runtime/vmOperations.hpp
No comments.
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/OneGetThreadListStackTraces.java
No comments.
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
L27: #include <errno.h>
This include is out of order; should be first in the list.
This file doesn't compile on my MBP13:
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp:49:14:
error: format specifies type 'unsigned long' but the argument has
type 'jmethodID' (aka '_jmethodID *') [-Werror,-Wformat]
fi1->method, fi2->method);
^~~~~~~~~~~
./open/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp:49:27:
error: format specifies type 'unsigned long' but the argument has
type 'jmethodID' (aka '_jmethodID *') [-Werror,-Wformat]
fi1->method, fi2->method);
^~~~~~~~~~~
2 errors generated.
This change made it compile on my MBP13, but that may break
it on
other platforms:
$ hg diff
diff -r 560847c69fbe
test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
---
a/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
Wed Jul 08 12:13:32 2020 -0400
+++
b/test/hotspot/jtreg/serviceability/jvmti/GetThreadListStackTraces/libOneGetThreadListStackTraces.cpp
Wed Jul 08 12:40:42 2020 -0400
@@ -46,7 +46,7 @@
if (fi1->method != fi2->method) { /*
jvmtiFrameInfo::method */
snprintf(err_msg, sizeof(err_msg),
"method is different: fi1 = %lx, fi2 = %lx",
- fi1->method, fi2->method);
+ (unsigned long) fi1->method, (unsigned long)
fi2->method);
env->FatalError(err_msg);
} else if (fi1->location != fi2->location) { /*
jvmtiFrameInfo::location */
snprintf(err_msg, sizeof(err_msg),
I'm not sure of the right platform independent way to output
the 'method' field.
Dan
On 7/8/20 4:04 AM, Yasumasa Suenaga wrote:
Hi David,
On 2020/07/08 15:27, David Holmes wrote:
Hi Yasumasa,
On 7/07/2020 6:54 pm, Yasumasa Suenaga wrote:
Hi David, Serguei,
Serguei, thank you for replying even though you are on vacaiton!
I uploaded new webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.07/
Diff from previous webrev:
http://hg.openjdk.java.net/jdk/submit/rev/77243b1dcbfe
c'tor of GetSingleStackTraceClosure has jthread argument in
this webrev.
Also it does not contain testcase for GetThreadListStackTraces
with all threads, and OneGetThreadListStackTraces would test
main thread only.
All those changes are fine in principle for me. One nit/suggestion:
src/hotspot/share/prims/jvmtiEnvBase.hpp
544 jthread _java_thread;
elsewhere "java_thread" refers to a JavaThread, so to avoid
confusion may I suggest this member be named _jthread.
I uploaded new webrev:
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.08/
Diff from previous webrev:
http://hg.openjdk.java.net/jdk/submit/rev/ca6263dbdc87
I'm going to be away for the next couple of days - sorry - but
will try to check email on this if I can.
Thanks!
Yasumasa
Thanks,
David
-----
Thanks,
Yasumasa
On 2020/07/07 15:13, David Holmes wrote:
On 7/07/2020 2:57 pm, Yasumasa Suenaga wrote:
Hi David,
On 2020/07/07 11:31, David Holmes wrote:
Hi Yasumasa,
Hard to keep up with the changes - especially without
incremental webrevs.
Sorry, I will upload diff from previous webrev in the next.
If GetSingleStackTraceClosure also took the jthread as a
constructor arg, then you wouldn't need to recreate a JNI
local handle when calling _collector.fill_frames. It's a
small simplification and not essential at this stage.
I think we should get jthread from an argument of do_thread()
because do_thread() would pass the thread which are stopped
certainly.
It might be simplification if we pass _calling_thread to
MultipleStackTracesCollector. `jthread` is only needed to
store jvmtiStackInfo.thread . What do you think?
I'm not quite sure what you mean.
I think there is a bit of a design wart with direct handshakes
in that do_thread takes the target JavaThread as an argument.
That's useful in a case where you want a HandshakeClosure that
can be applied to multiple threads, but that's not typically
what is needed with direct handshakes - there is only a single
target. With a single-target HandshakeClosure you can capture
all the "target" information for the operation in the closure
instance. So if the actual do_thread operation wants the
jthread corresponding to the target thread then we can store
that in the closure rather than recomputing it (you could
assert it is the same but that seems overkill to me).
For the test ... I don't see how
Java_GetThreadListStackTraces_checkCallStacks is a valid
test. It gets the stacks of all live threads, then uses that
information to use GetThreadListStackTraces to get the stack
for the same set of threads through a different API. It then
compares the two sets of stacks for each thread expecting
them to be the same, but that need only be the case for the
main thread. Other threads could potentially have a
different stack (e.g. if this test is run with JFR enabled
there will be additional threads found.) Further I would
have expected that there already exist tests that check
that, for a given thread (which may be suspended or known to
be blocked) the same stack is found through the two
different APIs.
vmTestbase/nsk/jvmti/unit/GetAllStackTraces/getallstktr001
would check all of threads via GetThreadListStackTraces() and
GetAllStackTraces(), so we might be able to remove
GetThreadListStackTraces.java from this webrev.
Yes. The existing test only examines a set of test threads
that are all blocked on a raw monitor. You do not need to
duplicate that test.
OTOH we don't have testcase for GetThreadListStackTraces()
with thread_count == 1, so we need to testcase for it (it is
OneGetThreadListStackTraces.java) It would check whether the
state of target thread is "waiting" before JNI call to call
GetThreadListStackTraces(),
Yes we need to test the special cases introduced by your
changes - totally agree - and OneGetThreadListStackTraces.java
is a good test for that.
and also I expect it would not be run with JFR. (it is not
described @run)
The arguments to run with JFR (or a bunch of other things) can
be passed to the jtreg test harness to be applied to all tests.
Of course we can check GetThreadListStackTraces() with main
thread, but it is not the test for direct handshake for other
thread.
Right - that test already exists as per the above.
Thanks,
David
Thanks,
Yasumasa
Thanks,
David
-----
On 6/07/2020 11:29 pm, Yasumasa Suenaga wrote:
Hi Serguei,
Thanks for your comment!
I think C++ is more simple to implement the test agent as
you said.
So I implement it in C++ in new webrev. Could you review
again?
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.06/
Also I refactored libGetThreadListStackTraces.cpp, and I've
kept exception check after IsSameObject().
Thanks,
Yasumasa
On 2020/07/06 16:32, serguei.spit...@oracle.com wrote:
Hi Yasumasa,
Thank you for the update.
I think, a pending exception after IsSameObject needs to
be checked.
The checkStackInfo() needs one more refactoring as I've
already suggested.
The body of the loop at L68-L78 should be converted to a
function check_frame_info.
The si1->frame_buffer[i] and si2->frame_buffer[i] will be
passed as fi1 and fi2.
The index can be passed as well.
I'm still suggesting to simplify the local exception_msg
to something shorter like err_msg or exc_msg.
I'm not sure using fatal is right here:
This fragment looks strange:
152 if ((*env)->IsSameObject(env,
stack_info[i].thread, thread)) {
153 target_info = &stack_info[i];
154 break;
155 } else if ((*env)->ExceptionOccurred(env)) {
156 (*env)->ExceptionDescribe(env);
157 (*env)->FatalError(env, __FILE__);
158 }
I expected it to be:
jboolean same = (*env)->IsSameObject(env,
stack_info[i].thread, thread);
if ((*env)->ExceptionOccurred(env)) {
(*env)->ExceptionDescribe(env);
(*env)->FatalError(env, __FILE__);
}
if (same) {
target_info = &stack_info[i];
break;
}
Would it better to port this agent to C++ to simplify this
code nicer?
Thanks,
Serguei
On 7/5/20 06:13, Yasumasa Suenaga wrote:
Hi Serguei,
Thanks for your comment!
I refactored testcase. Could you review again?
http://cr.openjdk.java.net/~ysuenaga/JDK-8242428/webrev.05/
It would check Java exception after IsSameObject() call.
Does it need?
Any exceptions are not described in JNI document[1], and
JNI implementation (jni_IsSameObject()) does not seem to
throw it.
Thanks,
Yasumasa
[1]
https://docs.oracle.com/en/java/javase/14/docs/specs/jni/functions.html#issameobject
On 2020/07/05 14:46, serguei.spit...@oracle.com wrote:
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
