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List: openjdk-serviceability-dev
Subject: Re: 8185005: Improve performance of ThreadMXBean.getThreadInfo(long ids[], int maxDepth)
From: "Daniel D. Daugherty" <daniel.daugherty () oracle ! com>
Date: 2019-08-14 18:25:07
Message-ID: 2bf948a5-1397-3459-030a-be9598b4e7fc () oracle ! com
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So based on the last three message on this thread:
webrev.05 is withdrawn for the moment
webrev.04 is the current webrev, but needs to have some startup time
issues resolved before moving forward.
I'm going to hold off on re-reviewing anything at the moment until
the dust settles...
Dan
On 8/12/19 7:34 PM, David Holmes wrote:
> Hi Daniil,
>
> On 13/08/2019 9:24 am, Daniil Titov wrote:
> > Hi Robbin,
> >
> > Thank you very much for reviewing this version of the fix! Based on
> > your findings
> > it seems as it makes sense to make a step back and continue with the
> > approach we took before in the previous version of the webrev
> > (webrev.04),
> > and get more information about the impact on the startup time it has.
> > I will
> > consult with Claus regarding this and then share the findings.
>
> That seems a good approach to me. It wasn't at all clear to me that
> the latest proposed approach would actually solve the original problem
> in a satisfactory way - it would depend on how constant the set of
> threads being queried was.
>
> There is no perfect solution here as any fix to the reported problem
> incurs overhead elsewhere. Even evaluating the merits of the different
> trade-offs is hard to do - we could end up with a compromise solution
> that fails to satisfy anyone.
>
> David
> -----
>
> > Thanks again,
> > --Daniil
> >
> >
> >
> >
> >
> >
> > On 8/12/19, 5:22 AM, "Robbin Ehn" <robbin.ehn@oracle.com> wrote:
> >
> > Hi Daniil,
> > I took a new deeper dive into this.
> > This line seems to have some issues:
> > if (ThreadTable::is_initialized() &&
> > thread->in_thread_table() &&
> > !thread->is_attaching_via_jni()) {
> > If you create new threads which attaches and then dies, the
> > table will just keep
> > growing. So you must remove them also ?
> > Secondly you should not use volatile semantics for
> > _in_thread_table.
> > The load in the if-statement can be reordered with _is_initialized.
> > Which could lead to a leak, rogue pointer in the table.
> > So both "static volatile bool _is_initialized;" and
> > "volatile bool
> > _in_thread_table; "
> > should be stored with store_release and loaded with load_acquire.
> > Unfortunately it looks like there still would be races if
> > ThreadTable::add_thread e.g. context switch at:
> > if (_local_table->insert(thread, lookup, entry)) {
> > // HERE
> > java_thread->set_in_thread_table(true);
> > *Remove side can pass the if-statement without removing.
> > Since this thread also maybe exiting at any moment, e.g.
> > context switch:
> > if (tobj != NULL && !thread->is_exiting() &&
> > java_tid == java_lang_Thread::thread_id(tobj)) {
> > // HERE
> > ThreadTable::add_thread(java_tid, thread);
> > *Add side can add a thread that is exiting.
> > Mixing in a third thread looking up a random tid and
> > getting a JavaThread*, it
> > must validate it against it's ThreadsList. Making the hashtable
> > useless.
> > So I think the only one adding and removing should be the
> > thread itself.
> > 1:Add to ThreadsList
> > 2:Add to ThreadTable
> > 3:Remove from ThreadTable
> > 4:Remove ThreadsList
> > Between 1-2 and 3-4 the thread would be looked-up via
> > linear scan.
> > I don't see an easy way around the start-up issue with this.
> > Maybe have the cache in Java.
> > Pass in the thread obj into a
> > java_sun_management_ThreadImpl_getThreadTotalCpuTime3 instead,
> > thus skipping any look-ups in native.
> > Thanks, Robbin
> > On 8/12/19 5:49 AM, Daniil Titov wrote:
> > > Hi David, Robbin, Daniel, and Serguei,
> > >
> > > Please review a new version of the fix.
> > >
> > > As David suggested I created a separated Jira issue [1] to
> > cover additional optimization for
> > > some callers of find_JavaThread_from_java_tid() and this
> > version of the fix no longer includes
> > > changes in management.cpp ( and the test related with these
> > changes).
> > >
> > > Regarding the impact the previous version of the fix had on
> > the thread startup time at heavy load (e.g.
> > > when 5000 threads are created and destroyed every second) I
> > tried a different approach that makes
> > > calls to ThreadTable::add_thread and
> > ThreadTable::remove_thread asynchronous and offloads the
> > > work for actual modifications of the thread table to a
> > periodic task that runs every 5 seconds. With the
> > > same stress test scenario (the test does some warm-up and
> > then measures the time it takes to create
> > > and start 100,000 threads; every thread just sleeps for 100
> > ms) the impact on the thread startup time
> > > was reduced to 1.2% ( from 2.7%).
> > >
> > > The cause of this impact in this stress test scenario is that
> > as soon as the thread table is initialized,
> > > an additional work to insert and delete entries in the thread
> > table should be performed, even if
> > > com.sun.management.ThreadMXBean methods are no longer called.
> > For example, In the stress test
> > > mentioned above, every second about 5000 entries had to be
> > inserted in the table and then deleted.
> > >
> > > That doesn't look right and the new version of the fix uses
> > the different approach: the thread is added to
> > > the thread table only when this thread is requested by
> > com.sun.management.ThreadMXBean bean. Every
> > > time when find_JavaThread_from_java_tid() is called for a new
> > tid, the thread is found by the iterating over
> > > the thread list and added to the thread table. All consequent
> > calls to find_JavaThread_from_java_tid() for
> > > the same tid returns the thread from the thread table.
> > >
> > > Running stress test for the cases when the thread table is
> > enabled and not showed no difference in the
> > > average thread startup times.
> > >
> > > [1] : https://bugs.openjdk.java.net/browse/JDK-8229391
> > >
> > > Bug: https://bugs.openjdk.java.net/browse/JDK-8185005
> > > Webrev: https://cr.openjdk.java.net/~dtitov/8185005/webrev.05/
> > >
> > > Thanks,
> > > Daniil
> > >
> > > On 8/4/19, 7:54 PM, "David Holmes" <david.holmes@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@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@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@oracle.com>
> > > > > > Organization: Oracle Corporation
> > > > > > Date: Friday, June 28, 2019 at 7:56 PM
> > > > > > To: Daniil Titov
> > <daniil.x.titov@oracle.com>, OpenJDK Serviceability
> > <serviceability-dev@openjdk.java.net>,
> > "hotspot-runtime-dev@openjdk.java.net"
> > <hotspot-runtime-dev@openjdk.java.net>, "jmx-dev@openjdk.java.net"
> > <jmx-dev@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@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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