8185005: Improve performance of ThreadMXBean.getThreadInfo(long ids[], int maxDepth)
David Holmes
david.holmes at oracle.com
Tue Sep 17 10:46:07 UTC 2019
Hi Serguei,
On 17/09/2019 7:10 pm, serguei.spitsyn at oracle.com wrote:
> Hi Daniil,
>
>
> On 9/16/19 21:36, Daniil Titov wrote:
>> Hi David,
>>
>> 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.
I'm not sure I follow. With the current code if two threads are racing
to initialize the ThreadTable with ThreadsLists that contain a different
set of threads then there are two possibilities with regards to the
interleaving. Assume T1 initializes the table with its set of threads
and so finds the tid it is looking for in the table. Meanwhile T2 is
racing with the initialization logic:
- If T2 sees _is_initialized then lazy_initialization does nothing for
T2, and the additional threads in its ThreadsList (say T3 and T4) are
not added to the table. But the specific thread associated with the tid
(say T3) will be found by linear search of the ThreadsList and then
added. If any other threads come searching for T4 they too will not find
it in the ThreadTable but instead perform the linear search of their
ThreadsList (and add it).
- if T2 doesn't see _is_initialized at first it will try to acquire the
lock, and eventually see _is_initialized is true, at which point it will
try to add all of its thread's to the table (so T3 and T4 will be
added). When lazy_initialize returns, T3 will be found in the table and
returned. If any other threads come searching for T4 they will also find
it in the table.
With your suggested code change this second case is not possible so for
any racing initialization the lookup of any threads not in the original
ThreadsList will always result in using the linear search before adding
to the table.
Both seem correct to me. Which one is more efficient will totally depend
on the number of differences between the ThreadsLists and whether the
code ever tries to look up those additional threads. If we assume racing
initialization is likely to be rare anyway (because generally one thread
is in charge of doing the monitoring) then the choice seems somewhat
arbitrary.
Cheers,
David
-----
> Thanks,
> Serguei
>
>> 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.holmes at 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.holmes at 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.holmes at 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.daugherty at 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.spitsyn at oracle.com>
>> > > > > > Organization: Oracle Corporation
>> > > > > > Date: Friday, June 28, 2019 at
>> 7:56 PM
>> > > > > > To: Daniil Titov
>> <daniil.x.titov at oracle.com>, OpenJDK Serviceability
>> <serviceability-dev at openjdk.java.net>,
>> "hotspot-runtime-dev at openjdk.java.net"
>> <hotspot-runtime-dev at openjdk.java.net>, "jmx-dev at openjdk.java.net"
>> <jmx-dev at 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.holmes at 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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>
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