RFR 8205113: Update JVMTI doc references to object allocation tracking

[Jeremy Manson]

Yup!  The paragraph meanders a bit.  How about something like:

Sent when the virtual machine allocates an
Object visible to Java programming language code without using a
<code>new</code> bytecode variant or a JNI method.
Many approaches to tracking object allocation use a combination of
bytecode-based instrumentation and <internallink id="jniIntercept">JNI
function
interception</internallink> to intercept allocations.  However, this
approach can leave a number of allocations undetected.  Allocations that
are neither
triggered by bytecode nor JNI are executed directly by the VM.
When those allocations occur, the VM should send this event.
Virtual machines that are incapable of bytecode instrumentation
for some or all of their methods may also send this event.
<p/>
Note that the <internallink
id="SampledObjectAlloc">SampledObjectAlloc</internallink>
event is triggered on all Java object allocations, including those
triggered by bytecode,
JNI methods, and VM events.



On Mon, Jun 18, 2018 at 12:57 AM David Holmes <david.holmes at oracle.com>
wrote:

> On 18/06/2018 5:01 PM, Jeremy Manson wrote:
> > We haven't changed when a VM issues "VM object allocation" events.
> >
> > There were references in the docs to a requirement to use bytecode
> > rewriting and JNI interception to track allocations.  With
> > SampledObjectAlloc, this is no longer the case - SampledObjectAlloc can
> > track them.  This change is supposed to remove the references to those
> > requirements, and provide suitable replacement text.
> >
> > VM object alloc has specific language about being able to use it to
> > track allocations that cannot be tracked with bytecode instrumentation
> > and JNI interception.  My goal in rephrasing was to make it clear that,
> > while you can still use it for this, you can also just use
> > SampledObjectAlloc for everything.
>
> Okay. That doesn't come across clearly to me - sorry. So you will now
> get both kinds of events for allocations done in the VM?
>
> Thanks,
> David
>
>
> > Jeremy
> >
> > On Sun, Jun 17, 2018 at 9:11 PM David Holmes <david.holmes at oracle.com
> > <mailto:david.holmes at oracle.com>> wrote:
> >
> >     Hi Jeremy,
> >
> >     On 16/06/2018 2:33 AM, Jeremy Manson wrote:
> >      > Hi all,
> >      >
> >      > There are a number of references in the JVMTI doc to its not doing
> >      > object allocation tracking.  Now that JEP 331 has landed, these
> >      > references are obsolete.  This patch changes those references
> >     accordingly.
> >      >
> >      > While I was there, I took the liberty of fixing some
> spelling errors.
> >      >
> >      > As far as I know, these are non-normative changes and modify no
> >     API, so
> >      > they should not require a CSR.
> >
> >     I'm unclear on the nature of the change to "VM Object Allocation".
> Does
> >     the existence of SampledObjectAlloc change when a VM should issue "VM
> >     object allocation" events?
> >
> >     Thanks,
> >     David
> >
> >      >
> >      > Bug:
> >      > https://bugs.openjdk.java.net/browse/JDK-8205113
> >      >
> >      > Webrev:
> >      > http://cr.openjdk.java.net/~jmanson/8205113/webrev.00/
> >      >
> >      > Thanks!
> >      >
> >      > Jeremy
> >
>
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