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. 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.
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.
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()
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.
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.
Best regards,
Daniil
From: "serguei.spit...@oracle.com" <serguei.spit...@oracle.com>
Date: Tuesday, September 17, 2019 at 1:53 AM
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,
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
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> > >
> > >
> >
> >
> >
>
>
>
