Hi Serguei,
void ThreadTable::lazy_initialize(const ThreadsList *threads) {
if (_is_initialized) {
return;
> }
MutexLocker ml(ThreadTableCreate_lock);
If I understood you correctly in the code snippet you sent you meant to use
Threads_lock, not ThreadTableCreate_lock, right?
The original idea was to do a minimal amount of work while holding the lock and
hold the lock for as short period of time as possible to not block other
threads when it is not necessary.
With the suggested approach no new threads could be started until the thread
table is created and
populated with all threads running inside a Java application and in case of
large app there could be
thousands of them.
And if we try to use 2 locks, ThreadTableCreate_lock as in your snippet and
then the nested Threads_lock around
thread->is_exiting() and add_thread(java_tid, thread) lines then it will not
work since the rank of Threads_lock
is higher than the rank of ThreadTableCreate_lock.
So choosing between blocking new threads from starting and potentially allowing
some other monitoring thread to do a one-time linear scan I think it makes
sense to choose the latter.
Thanks!
Best regards,
Daniil
From: "serguei.spit...@oracle.com" <serguei.spit...@oracle.com>
Date: Thursday, September 19, 2019 at 10:30 PM
To: Daniil Titov <daniil.x.ti...@oracle.com>, Robbin Ehn <robbin....@oracle.com>, David Holmes <david.hol...@oracle.com>,
<daniel.daughe...@oracle.com>, OpenJDK Serviceability <serviceability-dev@openjdk.java.net>,
"hotspot-runtime-...@openjdk.java.net" <hotspot-runtime-...@openjdk.java.net>, "jmx-...@openjdk.java.net"
<jmx-...@openjdk.java.net>, Claes Redestad <claes.redes...@oracle.com>
Subject: Re: RFR: 8185005: Improve performance of
ThreadMXBean.getThreadInfo(long ids[], int maxDepth)
Hi Daniil,
I think, it is better to grab the thread_lock just once at lazy initialization.
It would look simpler, something, like this would work:
void ThreadTable::lazy_initialize(const ThreadsList *threads) {
if (_is_initialized) {
return;
}
MutexLocker ml(ThreadTableCreate_lock);
if (_is_initialized) {
// There is no obvious benefits in allowing the thread table
// being concurrently populated during the initalization.
return;
}
create_table(threads->length());
_is_initialized = true;
for (uint i = 0; i < threads->length(); i++) {
JavaThread* thread = threads->thread_at(i);
oop tobj = thread->threadObj();
if (tobj != NULL) {
jlong java_tid = java_lang_Thread::thread_id(tobj);
if (!thread->is_exiting()) {
// Must be inside the lock to ensure that we don't add the thread to
the table
// that has just passed the removal point in
ThreadsSMRSupport::remove_thread()
add_thread(java_tid, thread);
}
}
}
}
Otherwise, concurrent executions of the find_JavaThread_from_java_tid()
will sometimes do a linear search of threads that are not included yet to
the ThreadTable from the ThreadsList (which is used for lazy initialization).
Instead, it is better to wait for the lazy_initialization() to complete.
Thanks,
Serguei
On 9/19/19 17:30, Daniil Titov wrote:
Hi David and Serguei,
Please review new version of the fix that includes the changes Serguei
suggested:
1. If racing threads initialize the thread table only one of these threads
will populate the table with the threads from the thread list
2. The code that adds the thread to the tread table is put inside
Threads_lock to ensure that we cannot accidentally add the thread
that has just passed the removal point in
ThreadsSMRSupport::remove_thread()
The changes are in ThreadTable::lazy_initialize() method only.
Testing: Mach5 tier1, tier2, tier3, tier4, and tier5 tests successfully passed.
Webrev: https://cr.openjdk.java.net/~dtitov/8185005/webrev.07/
Bug : https://bugs.openjdk.java.net/browse/JDK-8185005
Thank you!
--Daniil
On 9/18/19, 1:01 AM, mailto:serguei.spit...@oracle.com
mailto:serguei.spit...@oracle.com wrote:
Hi Daniil,
On 9/17/19 17:13, Daniil Titov wrote:
> Hi Serguei,
>
> Please find below my answers to the concerns you mentioned in the
previous email.
>
> 1.
> > I have a concern about the checks for thread->is_exiting().
> > - the lines 632-633 are useless as they do not really protect from
returning an exiting thread
>> It is interesting what might happen if an exiting thread is returned by
the
>> ThreadsList::find_JavaThread_from_java_tid ().
>> Does it make sense to develop a test that would cover these cases?
> I agree, it doesn't really provide any protection so it makes sense just
remove it.
Now, I'm not that confident about it. :)
> The current implementation
> find_JavaThread_from_java_tid() doesn't provide such protection as
well, since the thread could start exiting
> immediately after method find_JavaThread_from_java_tid() returns, so the
assumption is that the callers of
> find_JavaThread_from_java_tid() are expecting to deal with such threads
and looking on some of them shows that
> they usually try to retrieve threadObj or a thread statistic object and
if it is NULL that just do nothing.
If I understand it correctly, the jt->threadObj() can remain non-NULL
for some time while jt->is_exiting() == true.
It is not clear how reliable is to use it.
But this is a pre-existing issue. It is not you who introduced it. :)
So, we can skip it for now.
But for the record, we may have a source of intermittent issues.
> I'm not sure we could cover this specific case with the test. The window between find_JavaThread_from_java_tid() returns and the caller
> continues the execution is too small. The window between the thread
started exiting and removed itself from the thread table is very small as well.
Understand.
> 2.
>> - the lines 105-108 can result in adding exiting threads into the
ThreadTable
> I agree, it was missed, we need to wrap this code inside Thread_lock
in the similar way as it is done find_JavaThread_from_java_tid()
Okay, thanks!
> 3.
>> I would suggest to rewrite this fragment in a safe way:
>> 95 {
>> 96 MutexLocker ml(ThreadTableCreate_lock);
>> 97 if (!_is_initialized) {
>> 98 create_table(threads->length());
>> 99 _is_initialized = true;
>> 100 }
>> 101 }
>> as:
>> {
>> MutexLocker ml(ThreadTableCreate_lock);
>> if (_is_initialized) {
>> return;
> > }
> > create_table(threads->length());
> > _is_initialized = true;
> > }
>
> It was an intension to not block while populating the table with the
threads from the current thread list.
> There is no needs to have other threads that call
find_JavaThread_from_java_tid() be blocked and waiting for
> it to complete since the requested thread could be not present in the
thread list that triggers the thread table
> initialization. Plus in case of racing initialization it allows
threads from not original thread lists be added to the table
> and thus avoid the linear scan when these thread are looked up for the
first time.
I've replied to David in another email.
Let's talk once more about it tomorrow.
> 4.
>>> The case you have described is exact the reason why we still have a
code inside
>>> ThreadsList::find_JavaThread_from_java_tid() method that does a linear
scan and adds
>>> the requested thread to the thread table if it is not there ( lines
614-613 below).
>> I disagree because it is easy to avoid concurrent ThreadTable
>> initialization (please, see my separate email).
>> The reason for this code is to cover a case of late/lazy ThreadTable
>> initialization.
> David Holmes replied to this in a separate email providing a very
detailed
> explanation of the possible cases and how the proposed implementation
satisfies them.
Yes. Please, see above.
Thanks,
Serguei
> Best regards,
> Daniil
>
> From: mailto:serguei.spit...@oracle.com mailto:serguei.spit...@oracle.com
> Date: Tuesday, September 17, 2019 at 1:53 AM
> To: Daniil Titov mailto:daniil.x.ti...@oracle.com, Robbin Ehn
mailto:robbin....@oracle.com, David Holmes mailto:david.hol...@oracle.com,
mailto:daniel.daughe...@oracle.com, OpenJDK Serviceability
mailto:serviceability-dev@openjdk.java.net,
mailto:hotspot-runtime-...@openjdk.java.net
mailto:hotspot-runtime-...@openjdk.java.net, mailto:jmx-...@openjdk.java.net
mailto:jmx-...@openjdk.java.net, Claes Redestad mailto:claes.redes...@oracle.com
> Subject: Re: RFR: 8185005: Improve performance of
ThreadMXBean.getThreadInfo(long ids[], int maxDepth)
>
> Hi Daniil,
>
> Thank you for you patience in working on this issue!
> Also, I like that the current thread related optimizations in
management.cpp were factored out.
> It was a good idea to separate them.
>
> I have a concern about the checks for thread->is_exiting().
> The threads are added to and removed from the ThreadTable under
protection of Threads_lock.
> However, the thread->is_exiting() checks are not protected, and so, they
are racy.
>
> There is a couple of such checks to mention:
> 611 JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong
java_tid) const {
> 612 ThreadTable::lazy_initialize(this);
> 613 JavaThread* thread = ThreadTable::find_thread_by_tid(java_tid);
> 614 if (thread == NULL) {
> 615 // If the thread is not found in the table find it
> 616 // with a linear search and add to the table.
> 617 for (uint i = 0; i < length(); i++) {
> 618 thread = thread_at(i);
> 619 oop tobj = thread->threadObj();
> 620 // Ignore the thread if it hasn't run yet, has exited
> 621 // or is starting to exit.
> 622 if (tobj != NULL && java_tid ==
java_lang_Thread::thread_id(tobj)) {
> 623 MutexLocker ml(Threads_lock);
> 624 // Must be inside the lock to ensure that we don't add the
thread to the table
> 625 // that has just passed the removal point in
ThreadsSMRSupport::remove_thread()
> 626 if (!thread->is_exiting()) {
> 627 ThreadTable::add_thread(java_tid, thread);
> 628 return thread;
> 629 }
> 630 }
> 631 }
> 632 } else if (!thread->is_exiting()) {
> 633 return thread;
> 634 }
> 635 return NULL;
> 636 }
> ...
> 93 void ThreadTable::lazy_initialize(const ThreadsList *threads) {
> 94 if (!_is_initialized) {
> 95 {
> 96 MutexLocker ml(ThreadTableCreate_lock);
> 97 if (!_is_initialized) {
> 98 create_table(threads->length());
> 99 _is_initialized = true;
> 100 }
> 101 }
> 102 for (uint i = 0; i < threads->length(); i++) {
> 103 JavaThread* thread = threads->thread_at(i);
> 104 oop tobj = thread->threadObj();
> 105 if (tobj != NULL && !thread->is_exiting()) {
> 106 jlong java_tid = java_lang_Thread::thread_id(tobj);
> 107 add_thread(java_tid, thread);
> 108 }
> 109 }
> 110 }
> 111 }
>
> A thread may start exiting right after the checks at the lines 626 and
105.
> So that:
> - the lines 632-633 are useless as they do not really protect from
returning an exiting thread
> - the lines 105-108 can result in adding exiting threads into the
ThreadTable
>
> Please, note, the lines 626-629 are safe in terms of addition to the
ThreadTable as they
> are protected with the Threads_lock. But the returned thread still can
exit after that.
> It is interesting what might happen if an exiting thread is returned by
the
> ThreadsList::find_JavaThread_from_java_tid ().
>
> Does it make sense to develop a test that would cover these cases?
>
> Thanks,
> Serguei
>
>
> On 9/16/19 11:18, Daniil Titov wrote:
> Hello,
>
> After investigating with Claes the impact of this change on the
performance (thanks a lot Claes for helping with it!) the conclusion was that the
impact on the thread startup time is not a blocker for this change.
>
> I also measured the memory footprint using Native Memory Tracking and
results showed around 40 bytes per live thread.
>
> Please review a new version of the fix, webrev.06 [1]. Just to remind,
webrev.05 was abandoned and webrev.06 [1] is webrev.04 [3] minus changes in
src/hotspot/share/services/management.cpp (that were factored out to a separate
issue [4]) and plus a change in ThreadsList::find_JavaThread_from_java_tid()
method (please, see below) that addresses the problem Robbin found and puts the
code that adds a new thread to the thread table inside Threads_lock.
>
> src/hotspot/share/runtime/threadSMR.cpp
>
> 622 if (tobj != NULL && java_tid ==
java_lang_Thread::thread_id(tobj)) {
> 623 MutexLocker ml(Threads_lock);
> 624 // Must be inside the lock to ensure that we don't add the
thread to the table
> 625 // that has just passed the removal point in
ThreadsSMRSupport::remove_thread()
> 626 if (!thread->is_exiting()) {
> 627 ThreadTable::add_thread(java_tid, thread);
> 628 return thread;
> 629 }
> 630 }
>
> [1] Webrev: https://cr.openjdk.java.net/~dtitov/8185005/webrev.06
> [2] Bug: https://bugs.openjdk.java.net/browse/JDK-8185005
> [3] https://cr.openjdk.java.net/~dtitov/8185005/webrev.04
> [4] https://bugs.openjdk.java.net/browse/JDK-8229391
>
> Thank you,
> Daniil
>
>
>
> >
> > On 8/4/19, 7:54 PM, "David Holmes"
mailto:david.hol...@oracle.com wrote:
> >
> > Hi Daniil,
> >
> > On 3/08/2019 8:16 am, Daniil Titov wrote:
> > > Hi David,
> > >
> > > Thank you for your detailed review. Please review a
new version of the fix that includes
> > > the changes you suggested:
> > > - ThreadTableCreate_lock scope is reduced to cover the
creation of the table only;
> > > - ThreadTableCreate_lock is made
_safepoint_check_always;
> >
> > Okay.
> >
> > > - ServiceThread is no longer responsible for the
resizing of the thread table, instead,
> > > the thread table is changed to grow on demand by
the thread that is doing the addition;
> >
> > Okay - I'm happy to get the serviceThread out of the
picture here.
> >
> > > - fixed nits and formatting issues.
> >
> > Okay.
> >
> > >>> The change also includes additional optimization for
some callers of find_JavaThread_from_java_tid()
> > >>> as Daniel suggested.
> > >> Not sure it's best to combine these, but if they are
limited to the
> > >> changes in management.cpp only then that may be okay.
> > >
> > > The additional optimization for some callers of
find_JavaThread_from_java_tid() is
> > > limited to management.cpp (plus a new test) so I left
them in the webrev but
> > > I also could move it in the separate issue if required.
> >
> > I'd prefer this part of be separated out, but won't
insist. Let's see if
> > Dan or Serguei have a strong opinion.
> >
> > > > src/hotspot/share/runtime/threadSMR.cpp
> > > >755 jlong tid =
SharedRuntime::get_java_tid(thread);
> > > > 926 jlong tid =
SharedRuntime::get_java_tid(thread);
> > > > I think it cleaner/better to just use
> > > > jlong tid =
java_lang_Thread::thread_id(thread->threadObj());
> > > > as we know thread is not NULL, it is a JavaThread
and it has to have a
> > > > non-null threadObj.
> > >
> > > I had to leave this code unchanged since it turned out
the threadObj is null
> > > when VM is destroyed:
> > >
> > > V [libjvm.so+0xe165d7] oopDesc::long_field(int)
const+0x67
> > > V [libjvm.so+0x16e06c6]
ThreadsSMRSupport::add_thread(JavaThread*)+0x116
> > > V [libjvm.so+0x16d1302] Threads::add(JavaThread*,
bool)+0x82
> > > V [libjvm.so+0xef8369]
attach_current_thread.part.197+0xc9
> > > V [libjvm.so+0xec136c] jni_DestroyJavaVM+0x6c
> > > C [libjli.so+0x4333] JavaMain+0x2c3
> > > C [libjli.so+0x8159] ThreadJavaMain+0x9
> >
> > This is actually nothing to do with the VM being
destroyed, but is an
> > issue with JNI_AttachCurrentThread and its interaction
with the
> > ThreadSMR iterators. The attach process is:
> > - create JavaThread
> > - mark as "is attaching via jni"
> > - add to ThreadsList
> > - create java.lang.Thread object (you can only execute
Java code after
> > you are attached)
> > - mark as "attach completed"
> >
> > So while a thread "is attaching" it will be seen by the
ThreadSMR thread
> > iterator but will have a NULL java.lang.Thread object.
> >
> > We special-case attaching threads in a number of places
in the VM and I
> > think we should be explicitly doing something here to
filter out
> > attaching threads, rather than just being tolerant of a
NULL j.l.Thread
> > object. Specifically in ThreadsSMRSupport::add_thread:
> >
> > if (ThreadTable::is_initialized() &&
!thread->is_attaching_via_jni()) {
> > jlong tid =
java_lang_Thread::thread_id(thread->threadObj());
> > ThreadTable::add_thread(tid, thread);
> > }
> >
> > Note that in ThreadsSMRSupport::remove_thread we can use
the same guard,
> > which covers the case the JNI attach encountered an
error trying to
> > create the j.l.Thread object.
> >
> > >> src/hotspot/share/services/threadTable.cpp
> > >> 71 static uintx get_hash(Value const& value,
bool* is_dead) {
> > >
> > >> The is_dead parameter still bothers me here. I can't
make enough sense
> > >> out of the template code in ConcurrentHashtable to
see why we have to
> > >> have it, but I'm concerned that its very existence
means we perhaps
> > >> should not be trying to extend CHT in this context. ??
> > >
> > > My understanding is that is_dead parameter provides a
mechanism for
> > > ConcurrentHashtable to remove stale entries that were
not explicitly
> > > removed by calling ConcurrentHashTable::remove()
method.
> > > I think that just because in our case we don't use
this mechanism doesn't
> > > mean we should not use ConcurrentHashTable.
> >
> > Can you confirm that this usage is okay with Robbin Ehn
please. He's
> > back from vacation this week.
> >
> > >> I would still want to see what impact this has on
thread
> > >> startup cost, both with and without the table being
initialized.
> > >
> > > I run a test that initializes the table by calling
ThreadMXBean.get getThreadInfo(),
> > > starts some threads as a worm-up, and then creates and
starts 100,000 threads
> > > (each thread just sleeps for 100 ms). In case when the
thread table is enabled
> > > 100,000 threads are created and started for about
15200 ms. If the thread table
> > > is off the test takes about 14800 ms. Based on this
information the enabled
> > > thread table makes the thread startup about 2.7%
slower.
> >
> > That doesn't sound very good. I think we may need to
Claes involved to
> > help investigate overall performance impact here.
> >
> > > Webrev:
https://cr.openjdk.java.net/~dtitov/8185005/webrev.04/
> > > Bug: https://bugs.openjdk.java.net/browse/JDK-8185005
> >
> > No further code comments.
> >
> > I didn't look at the test in detail.
> >
> > Thanks,
> > David
> >
> > > Thanks!
> > > --Daniil
> > >
> > >
> > > On 7/29/19, 12:53 AM, "David Holmes"
mailto:david.hol...@oracle.com wrote:
> > >
> > > Hi Daniil,
> > >
> > > Overall I think this is a reasonable approach but
I would still like to
> > > see some performance and footprint numbers, both
to verify it fixes the
> > > problem reported, and that we are not getting
penalized elsewhere.
> > >
> > > On 25/07/2019 3:21 am, Daniil Titov wrote:
> > > > Hi David, Daniel, and Serguei,
> > > >
> > > > Please review the new version of the fix, that
makes the thread table initialization on demand and
> > > > moves it inside
ThreadsList::find_JavaThread_from_java_tid(). At the creation time the thread table
> > > > is initialized with the threads from the
current thread list. We don't want to hold Threads_lock
> > > > inside find_JavaThread_from_java_tid(), thus
new threads still could be created while the thread
> > > > table is being initialized . Such threads will
be found by the linear search and added to the thread table
> > > > later, in
ThreadsList::find_JavaThread_from_java_tid().
> > >
> > > The initialization allows the created but
unpopulated, or partially
> > > populated, table to be seen by other threads - is
that your intention?
> > > It seems it should be okay as the other threads
will then race with the
> > > initializing thread to add specific entries, and
this is a concurrent
> > > map so that should be functionally correct. But
if so then I think you
> > > can also reduce the scope of the
ThreadTableCreate_lock so that it
> > > covers creation of the table only, not the
initial population of the table.
> > >
> > > I like the approach of only initializing the
table when needed and using
> > > that to control when the add/remove-thread code
needs to update the
> > > table. But I would still want to see what impact
this has on thread
> > > startup cost, both with and without the table
being initialized.
> > >
> > > > The change also includes additional
optimization for some callers of find_JavaThread_from_java_tid()
> > > > as Daniel suggested.
> > >
> > > Not sure it's best to combine these, but if they
are limited to the
> > > changes in management.cpp only then that may be
okay. It helps to be
> > > able to focus on the table related changes
without being distracted by
> > > other optimizations.
> > >
> > > > That is correct that ResolvedMethodTable was
used as a blueprint for the thread table, however, I tried
> > > > to strip it of the all functionality that is
not required in the thread table case.
> > >
> > > The revised version seems better in that regard.
But I still have a
> > > concern, see below.
> > >
> > > > We need to have the thread table resizable and
allow it to grow as the number of threads increases to avoid
> > > > reserving excessive memory a-priori or
deteriorating lookup times. The ServiceThread is responsible for
> > > > growing the thread table when required.
> > >
> > > Yes but why? Why can't this table be grown on
demand by the thread that
> > > is doing the addition? For other tables we may
have to delegate to the
> > > service thread because the current thread cannot
perform the action, or
> > > it doesn't want to perform it at the time the
need for the resize is
> > > detected (e.g. its detected at a safepoint and
you want the resize to
> > > happen later outside the safepoint). It's not
apparent to me that such
> > > restrictions apply here.
> > >
> > > > There is no ConcurrentHashTable available in
Java 8 and for backporting this fix to Java 8 another implementation
> > > > of the hash table, probably originally
suggested in the patch attached to the JBS issue, should be used. It will make
> > > > the backporting more complicated, however,
adding a new Implementation of the hash table in Java 14 while it
> > > > already has ConcurrentHashTable doesn't seem
reasonable for me.
> > >
> > > Ok.
> > >
> > > > Webrev:
http://cr.openjdk.java.net/~dtitov/8185005/webrev.03
> > >
> > > Some specific code comments:
> > >
> > > src/hotspot/share/runtime/mutexLocker.cpp
> > >
> > > + def(ThreadTableCreate_lock ,
PaddedMutex , special,
> > > false, Monitor::_safepoint_check_never);
> > >
> > > I think this needs to be a
_safepoint_check_always lock. The table will
> > > be created by regular JavaThreads and they should
(nearly) always be
> > > checking for safepoints if they are going to
block acquiring the lock.
> > > And it isn't at all obvious that the thread doing
the creation can't go
> > > to a safepoint whilst this lock is held.
> > >
> > > ---
> > >
> > > src/hotspot/share/runtime/threadSMR.cpp
> > >
> > > Nit:
> > >
> > > 618 JavaThread* thread = thread_at(i);
> > >
> > > you could reuse the new java_thread local you
introduced at line 613 and
> > > just rename that "new" variable to "thread" so
you don't have to change
> > > all other uses.
> > >
> > > 628 } else if (java_thread != NULL && ...
> > >
> > > You don't need to check != NULL here as you only
get here when
> > > java_thread is not NULL.
> > >
> > > 755 jlong tid =
SharedRuntime::get_java_tid(thread);
> > > 926 jlong tid =
SharedRuntime::get_java_tid(thread);
> > >
> > > I think it cleaner/better to just use
> > >
> > > jlong tid =
java_lang_Thread::thread_id(thread->threadObj());
> > >
> > > as we know thread is not NULL, it is a JavaThread
and it has to have a
> > > non-null threadObj.
> > >
> > > ---
> > >
> > > src/hotspot/share/services/management.cpp
> > >
> > > 1323 if (THREAD->is_Java_thread()) {
> > > 1324 JavaThread* current_thread =
(JavaThread*)THREAD;
> > >
> > > These calls can only be made on a JavaThread so
this be simplified to
> > > remove the is_Java_thread() call. Similarly in
other places.
> > >
> > > ---
> > >
> > > src/hotspot/share/services/threadTable.cpp
> > >
> > > 55 class ThreadTableEntry : public
CHeapObj<mtInternal> {
> > > 56 private:
> > > 57 jlong _tid;
> > >
> > > I believe hotspot style is to not indent the
access modifiers in C++
> > > class declarations, so the above would just be:
> > >
> > > 55 class ThreadTableEntry : public
CHeapObj<mtInternal> {
> > > 56 private:
> > > 57 jlong _tid;
> > >
> > > etc.
> > >
> > > 60 ThreadTableEntry(jlong tid, JavaThread*
java_thread) :
> > > 61 _tid(tid),_java_thread(java_thread) {}
> > >
> > > line 61 should be indented as it continues line
60.
> > >
> > > 67 class ThreadTableConfig : public AllStatic {
> > > ...
> > > 71 static uintx get_hash(Value const&
value, bool* is_dead) {
> > >
> > > The is_dead parameter still bothers me here. I
can't make enough sense
> > > out of the template code in ConcurrentHashtable
to see why we have to
> > > have it, but I'm concerned that its very
existence means we perhaps
> > > should not be trying to extend CHT in this
context. ??
> > >
> > > 115 size_t start_size_log = size_log >
DefaultThreadTableSizeLog
> > > 116 ? size_log : DefaultThreadTableSizeLog;
> > >
> > > line 116 should be indented, though in this case
I think a better layout
> > > would be:
> > >
> > > 115 size_t start_size_log =
> > > 116 size_log > DefaultThreadTableSizeLog
? size_log :
> > > DefaultThreadTableSizeLog;
> > >
> > > 131 double ThreadTable::get_load_factor() {
> > > 132 return (double)_items_count/_current_size;
> > > 133 }
> > >
> > > Not sure that is doing what you want/expect. It
will perform integer
> > > division and then cast that whole integer to a
double. If you want
> > > double arithmetic you need:
> > >
> > > return ((double)_items_count)/_current_size;
> > >
> > > 180 jlong _tid;
> > > 181 uintx _hash;
> > >
> > > Nit: no need for all those spaces before the
variable name.
> > >
> > > 183 ThreadTableLookup(jlong tid)
> > > 184 : _tid(tid), _hash(primitive_hash(tid))
{}
> > >
> > > line 184 should be indented.
> > >
> > > 201 ThreadGet():_return(NULL) {}
> > >
> > > Nit: need space after :
> > >
> > > 211 assert(_is_initialized, "Thread table is not
initialized");
> > > 212 _has_work = false;
> > >
> > > line 211 is indented one space too far.
> > >
> > > 229 ThreadTableEntry* entry = new
ThreadTableEntry(tid,java_thread);
> > >
> > > Nit: need space after ,
> > >
> > > 252 return _local_table->remove(thread,lookup);
> > >
> > > Nit: need space after ,
> > >
> > > Thanks,
> > > David
> > > ------
> > >
> > > > Bug:
https://bugs.openjdk.java.net/browse/JDK-8185005
> > > >
> > > > Thanks!
> > > > --Daniil
> > > >
> > > >
> > > > On 7/8/19, 3:24 PM, "Daniel D. Daugherty"
mailto:daniel.daughe...@oracle.com wrote:
> > > >
> > > > On 6/29/19 12:06 PM, Daniil Titov wrote:
> > > > > Hi Serguei and David,
> > > > >
> > > > > Serguei is right,
ThreadTable::find_thread(java_tid) cannot return a JavaThread with an unmatched java_tid.
> > > > >
> > > > > Please find a new version of the fix
that includes the changes Serguei suggested.
> > > > >
> > > > > Regarding the concern about the
maintaining the thread table when it may never even be queried, one of
> > > > > the options could be to add ThreadTable
::isEnabled flag, set it to "false" by default, and wrap the calls to the thread table
> > > > > in ThreadsSMRSupport add_thread() and
remove_thread() methods to check this flag.
> > > > >
> > > > > When
ThreadsList::find_JavaThread_from_java_tid() is called for the first time it could check if
ThreadTable ::isEnabled
> > > > > Is on and if not then set it on and
populate the thread table with all existing threads from the thread list.
> > > >
> > > > I have the same concerns as David H. about
this new ThreadTable.
> > > >
ThreadsList::find_JavaThread_from_java_tid() is only called from code
> > > > in
src/hotspot/share/services/management.cpp so I think that table
> > > > needs to enabled and populated only if it
is going to be used.
> > > >
> > > > I've taken a look at the webrev below and
I see that David has
> > > > followed up with additional comments.
Before I do a crawl through
> > > > code review for this, I would like to see
the ThreadTable stuff
> > > > made optional and David's other comments
addressed.
> > > >
> > > > Another possible optimization is for
callers of
> > > > find_JavaThread_from_java_tid() to save
the calling thread's
> > > > tid value before they loop and if the
current tid == saved_tid
> > > > then use the current JavaThread* instead
of calling
> > > > find_JavaThread_from_java_tid() to get the
JavaThread*.
> > > >
> > > > Dan
> > > >
> > > > >
> > > > > Webrev:
https://cr.openjdk.java.net/~dtitov/8185005/webrev.02/
> > > > > Bug:
https://bugs.openjdk.java.net/browse/JDK-8185005
> > > > >
> > > > > Thanks!
> > > > > --Daniil
> > > > >
> > > > > From: mailto:serguei.spit...@oracle.com
> > > > > Organization: Oracle Corporation
> > > > > Date: Friday, June 28, 2019 at 7:56 PM
> > > > > To: Daniil Titov
mailto:daniil.x.ti...@oracle.com, OpenJDK Serviceability
mailto:serviceability-dev@openjdk.java.net, mailto:hotspot-runtime-...@openjdk.java.net
mailto:hotspot-runtime-...@openjdk.java.net, mailto:jmx-...@openjdk.java.net
mailto:jmx-...@openjdk.java.net
> > > > > Subject: Re: RFR: 8185005: Improve
performance of ThreadMXBean.getThreadInfo(long ids[], int maxDepth)
> > > > >
> > > > > Hi Daniil,
> > > > >
> > > > > I have several quick comments.
> > > > >
> > > > > The indent in the hotspot c/c++ files
has to be 2, not 4.
> > > > >
> > > > >
https://cr.openjdk.java.net/~dtitov/8185005/webrev.01/src/hotspot/share/runtime/threadSMR.cpp.frames.html
> > > > > 614 JavaThread*
ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
> > > > > 615 JavaThread* java_thread =
ThreadTable::find_thread(java_tid);
> > > > > 616 if (java_thread == NULL &&
java_tid == PMIMORDIAL_JAVA_TID) {
> > > > > 617 //
ThreadsSMRSupport::add_thread() is not called for the primordial
> > > > > 618 // thread. Thus, we find
this thread with a linear search and add it
> > > > > 619 // to the thread table.
> > > > > 620 for (uint i = 0; i <
length(); i++) {
> > > > > 621 JavaThread* thread =
thread_at(i);
> > > > > 622 if
(is_valid_java_thread(java_tid,thread)) {
> > > > > 623
ThreadTable::add_thread(java_tid, thread);
> > > > > 624 return thread;
> > > > > 625 }
> > > > > 626 }
> > > > > 627 } else if (java_thread != NULL
&& is_valid_java_thread(java_tid, java_thread)) {
> > > > > 628 return java_thread;
> > > > > 629 }
> > > > > 630 return NULL;
> > > > > 631 }
> > > > > 632 bool
ThreadsList::is_valid_java_thread(jlong java_tid, JavaThread* java_thread) {
> > > > > 633 oop tobj =
java_thread->threadObj();
> > > > > 634 // Ignore the thread if it
hasn't run yet, has exited
> > > > > 635 // or is starting to exit.
> > > > > 636 return (tobj != NULL &&
!java_thread->is_exiting() &&
> > > > > 637 java_tid ==
java_lang_Thread::thread_id(tobj));
> > > > > 638 }
> > > > >
> > > > > 615 JavaThread* java_thread =
ThreadTable::find_thread(java_tid);
> > > > >
> > > > > I'd suggest to rename find_thread()
to find_thread_by_tid().
> > > > >
> > > > > A space is missed after the comma:
> > > > > 622 if
(is_valid_java_thread(java_tid,thread)) {
> > > > >
> > > > > An empty line is needed before L632.
> > > > >
> > > > > The name 'is_valid_java_thread' looks
wrong (or confusing) to me.
> > > > > Something like
'is_alive_java_thread_with_tid()' would be better.
> > > > > It'd better to list parameters in the
opposite order.
> > > > >
> > > > > The call to is_valid_java_thread() is
confusing:
> > > > > 627 } else if (java_thread != NULL
&& is_valid_java_thread(java_tid, java_thread)) {
> > > > >
> > > > > Why would the call
ThreadTable::find_thread(java_tid) return a JavaThread with an unmatched java_tid?
> > > > >
> > > > >
> > > > > Thanks,
> > > > > Serguei
> > > > >
> > > > > On 6/28/19, 9:40 PM, "David Holmes"
mailto:david.hol...@oracle.com wrote:
> > > > >
> > > > > Hi Daniil,
> > > > >
> > > > > The definition and use of this
hashtable (yet another hashtable
> > > > > implementation!) will need careful
examination. We have to be concerned
> > > > > about the cost of maintaining it
when it may never even be queried. You
> > > > > would need to look at footprint
cost and performance impact.
> > > > >
> > > > > Unfortunately I'm just about to
board a plane and will be out for the
> > > > > next few days. I will try to look
at this asap next week, but we will
> > > > > need a lot more data on it.
> > > > >
> > > > > Thanks,
> > > > > David
> > > > >
> > > > > On 6/28/19 3:31 PM, Daniil Titov wrote:
> > > > > Please review the change that improves
performance of ThreadMXBean MXBean methods returning the
> > > > > information for specific threads. The
change introduces the thread table that uses ConcurrentHashTable
> > > > > to store one-to-one the mapping between
the thread ids and JavaThread objects and replaces the linear
> > > > > search over the thread list in
ThreadsList::find_JavaThread_from_java_tid(jlong tid) method with the lookup
> > > > > in the thread table.
> > > > >
> > > > > Testing: Mach5 tier1,tier2 and tier3
tests successfully passed.
> > > > >
> > > > > Webrev:
https://cr.openjdk.java.net/~dtitov/8185005/webrev.01/
> > > > > Bug:
https://bugs.openjdk.java.net/browse/JDK-8185005
> > > > >
> > > > > Thanks!
> > > > >
> > > > > Best regards,
> > > > > Daniil
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> > >
> >
> >
> >
>
>
>
>
>
>
>
>
>
>
>
