The
assumption is that it's quite uncommon and even if this is the case
the linear scan happens
only once per such thread.
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 }
Thanks,
Daniil
On 9/16/19, 7:27 PM, "David Holmes" <david.hol...@oracle.com> wrote:
Hi Daniil,
Thanks again for your perseverance on this one.
I think there is a problem with initialization of the thread table.
Suppose thread T1 has called
ThreadsList::find_JavaThread_from_java_tid
and has commenced execution of ThreadTable::lazy_initialize, but
not yet
marked _is_initialized as true. Now two new threads (T2 and T3) are
created and start running - they aren't added to the ThreadTable yet
because it isn't initialized. Now T0 also calls
ThreadsList::find_JavaThread_from_java_tid using an updated
ThreadsList
that contains T2 and T3. It also calls
ThreadTable::lazy_initialize. If
_is_initialized is still false T0 will attempt initialization but
once
it gets the lock it will see the table has now been initialized
by T1.
It will then proceed to update the table with its own ThreadList
content
- adding T2 and T3. That is all fine. But now suppose T0
initially sees
_is_initialized as true, it will do nothing in lazy_initialize and
simply return to find_JavaThread_from_java_tid. But now T2 and T3
are
missing from the ThreadTable and nothing will cause them to be
added.
More generally any ThreadsList that is created after the ThreadsList
that will be used for initialization, may contain threads that
will not
be added to the table.
Thanks,
David
On 17/09/2019 4:18 am, 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"
<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"
<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" <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: <serguei.spit...@oracle.com>
> > > > > Organization: Oracle Corporation
> > > > > Date: Friday, June 28, 2019 at
7:56 PM
> > > > > To: Daniil Titov
<daniil.x.ti...@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>
> > > > > 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" <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
> > > > >
> > > > >
> > > > >
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