CSR reviewed.
management.cpp
2083 java_thread = (JavaThread*)THREAD;
2084 if (java_thread->is_Java_thread()) {
2085 return java_thread->cooked_allocated_bytes();
2086 }
The cast should be done after is_Java_thread() test.
ThreadImpl.java
162 private void throwIfNullThreadIds(long[] ids) {
Even better: simply use Objects::requiresNonNull and this method can be
removed.
This suggests positive naming alternative to
throwIfThreadAllocatedMemoryNotSupported -
"ensureThreadAllocatedMemorySupported" (sorry I should have suggested that)
ThreadMXBean.java
130 * @throws java.lang.UnsupportedOperationException if the Java
virtual
Nit: "java.lang." can be dropped.
@since 14 is missing.
Mandy
On 8/30/19 3:33 PM, Hohensee, Paul wrote:
Thanks for your review, Mandy. Revised webrev at
http://cr.openjdk.java.net/~phh/8207266/webrev.02/.
I updated the CSR with your suggested javadoc for
getCurrentThreadAllocatedBytes. It now matches that for
getCurrentThreadUserTime and getCurrentThreadCputime. I also fixed the
“convenient” -> “convenience” typos in j.l.m.ThreadMXBean.java.
I meant GetOneThreads to be the possessive, but don’t feel strongly
either way so I’m fine with GetOneThread.
I updated ThreadImpl.java as you suggested, though in
getThreadAllocatedBytes(long[] ids) I had to add a
redundant-in-the-not-length-1-case check for a null ids reference.
Would someone take a look at the Hotspot side and the test please?
Paul
*From: *Mandy Chung <[email protected]>
*Date: *Friday, August 30, 2019 at 10:22 AM
*To: *"Hohensee, Paul" <[email protected]>
*Cc: *OpenJDK Serviceability <[email protected]>,
"[email protected]" <[email protected]>
*Subject: *Re: RFR (M): 8207266:
ThreadMXBean::getThreadAllocatedBytes() can be quicker for self thread
OK. That's better. Some review comments:
The javadoc of getCurrentThreadAllocatedBytes() can simply say:
"Returns an approximation of the total amount of memory, in bytes,
allocated in heap memory for the current thread.
This is a convenient method for local management use and is equivalent
to calling getThreadAllocatedBytes(Thread.currentThread().getId()).
src/hotspot/share/include/jmm.h
GetOneThreadsAllocatedMemory: s/OneThreads/OneThread/
sun/management/ThreadImpl.java
43 private static final String
THREAD_ALLOCATED_MEMORY_NOT_SUPPORTED =
44 "Thread allocated memory measurement is not supported.";
if (!isThreadAllocatedMemorySupported()) {
throw new
UnsupportedOperationException(THREAD_ALLOCATED_MEMORY_NOT_SUPPORTED);
}
Perhaps the above can be refactored as
throwIfAllocatedMemoryUnsupported() method.
391 if (ids.length == 1) {
392 sizes[0] = -1;
:
398 if (ids.length == 1) {
399 long id = ids[0];
400 sizes[0] = getThreadAllocatedMemory0(
401 Thread.currentThread().getId() == id ? 0 : id);
402 } else {
It seems cleaner to handle the 1-element array case at the beginning
of this method:
if (ids.length == 1) {
long size = getThreadAllocatedBytes(ids[0]);
return new long[] { size };
}
I didn't review the hotspot implementation and the test.
Mandy
On 8/29/19 10:01 AM, Hohensee, Paul wrote:
My bad, Mandy. The webrev puts getCurrentThreadAllocatedBytes in
com.sun.management.ThreadMXBean along with the current two
getThreadAllocatedBytes methods for the reasons you list. I’ve
updated the CSR to specify com.sun.management and added a
rationale. AllocatedBytes is currently enabled by Hotspot by
default because the overhead of recording TLAB occupancy is
negligible.
There’s no new GC code, nor will there be, so imo we don’t have to
involve the GC folks. I.e., the new JMM method
GetOneThreadsAllocatedBytes uses the existing
cooked_allocated_bytes JavaThread method, and
getCurrentThreadAllocatedBytes is the same as
getThreadAllocatedBytes: it just bypasses the thread lookup code.
I hadn’t tracked down what happens when getCurrentThreadUserTime
and getCurrentThreadCpuTime are called before, but if I’m not
mistaken, it the code in jcmd() in attachListener.cpp will call
GetThreadCpuTimeWithKind in management.cpp, and it will ultimately
use Thread::current() as the subject of the call, see
os::current_thread_cpu_time in os_linux.cpp. That means that the
CurrentThread methods should work remotely the same way they do
locally. GetOneThreadsAllocatedBytes in management.cpp uses THREAD
as its subject when called on behalf of
getCurrentThreadAllocatedBytes, so it will also uses the current
remote Java thread. Even if these methods only worked locally,
there are many setups where apps are self-monitoring that could
use the performance improvement.
Thanks,
Paul
*From: *Mandy Chung <[email protected]>
<mailto:[email protected]>
*Date: *Wednesday, August 28, 2019 at 3:59 PM
*To: *"Hohensee, Paul" <[email protected]>
<mailto:[email protected]>
*Cc: *OpenJDK Serviceability <[email protected]>
<mailto:[email protected]>,
"[email protected]"
<mailto:[email protected]>
<[email protected]>
<mailto:[email protected]>
*Subject: *Re: RFR (M): 8207266:
ThreadMXBean::getThreadAllocatedBytes() can be quicker for self thread
Hi Paul,
The CSR proposes this method in java.lang.management.ThreadMXBean
as a Java SE feature.
Has this been discussed with the GC team to commit measuring
current thread's allocated bytes as Java SE feature? Can this be
supported by all JVM implementation? What is the overhead if
this is enabled by default? Does it need to be disabled? This
metric is from TLAB that might be okay. This needs
advice/discussion with GC experts.
I see that CSR mentions it can be disabled and link to
isThreadAllocatedMemoryEnabled() and
setThreadAllocatedMemoryEnabled() methods but these methods are
defined in com.sun.management.ThreadMXBean.
As Alan points out, current thread makes sense only in local VM
management. When this is monitored from a JMX client (e.g.
jconsole to connect to a running JVM,
"currentThreadAllowcatedBytes" attribute is the current thread in
jconsole process which invoking Thread::currentThread?
Mandy
On 8/28/19 12:22 PM, Hohensee, Paul wrote:
Please review a performance improvement for
ThreadMXBean.getThreadAllocatedBytes and the addition of
getCurrentThreadAllocatedBytes.
JBS issue:https://bugs.openjdk.java.net/browse/JDK-8207266
Webrev:http://cr.openjdk.java.net/~phh/8207266/webrev.00/
CSR:https://bugs.openjdk.java.net/browse/JDK-8230311
Previous email threads:
https://mail.openjdk.java.net/pipermail/serviceability-dev/2018-July/024441.html
https://mail.openjdk.java.net/pipermail/serviceability-dev/2018-August/024763.html
The CSR is for adding
ThreadMXBean.getCurrentThreadAllocatedBytes. I’d be great for
someone to review it.
I took Mandy’s advice and put the fast paths in the library
code. I added a new JMM method GetOneThreadsAllocatedBytes
that works the same as GetThreadCpuTime: it uses a thread_id
value of zero to distinguish the current thread. On my Mac
laptop, the result runs 47x faster for the current thread than
the old implementation.
The 3 tests intest/jdk/com/sun/management/ThreadMXBean all
pass. I added code to ThreadAllocatedMemory.java to test
getCurrentThreadAllocatedBytes as well as variations on
getThreadAllocatedBytes(id). A submit repo job is in progress.
Thanks,
Paul
