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List:       openjdk-serviceability-dev
Subject:    Re: RFR: 8252657: JVMTI agent is not unloaded when Agent_OnAttach is failed
From:       Yasumasa Suenaga <ysuenaga () openjdk ! java ! net>
Date:       2020-12-18 5:11:56
Message-ID: wyU3xsHa3EXTr1jzBroKJ-9iotf24FOdlkQh1a-aIxI=.4af560f3-8487-4be9-bfb2-5bea0dee74ee () github ! com
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On Tue, 1 Dec 2020 01:43:15 GMT, Chris Plummer <cjplummer@openjdk.org> wrote:

> > > * Q1: Is it necessary to call the Agent_OnUnload()?
> > 
> > [JVMTI spec of Agent_OnUnload()](https://docs.oracle.com/en/java/javase/15/docs/specs/jvmti.html#onunload) \
> > says this function will be called when the agent library will be unloaded by \
> > platform specific mechanism. OTOH it also says `Agent_OnUnload()` will be called \
> > both at VM termination and **by other reasons**. The spec don't say for the case \
> > if `Agent_OnAttach()` would be failed. IMHO `Agent_OnUnload()` should be called \
> > because this PR would unload library if `Agent_OnAttach()` failed. 
> > > * Q2: Would it be a JVMTI spec violation to call the Agent_OnAttach() multiple \
> > > times? (It seems to be the case to me.)
> > 
> > `Agent_OnAttach()` should be called only once per attach request, but VM should \
> > accept multiple attach request for same agent library. 
> > For example, we can add multiple `-agentlib` and `-agentpath` request as below. \
> > JVMTI agent might change behavior due to arguments or configuration file. 
> > -agentlib:test=profile=A -agentlib:test=profile=B \
> > -agentpath:/path/to/libtest=profile=C 
> > Agent developers should have responsibility for the behavior when more than one \
> > agent is loaded at a time. 
> > > * Q3: What has to be done for statically linked agent?
> > 
> > JVMTI spec says "unless it is statically linked into the executable", so I think \
> > we can ignore about Agent_OnUnload_L() in this PR. 
> > > * Q4: Should the agent be correctly loadable in the first place? What were the \
> > > reasons its loading to fail?
> > 
> > Agent (`Agent_OnAttach()`) might fail due to error in agent logic. For example, \
> > some agents load configuration file at initialization. If the user gives wrong \
> > value, it will fail. 
> > > Yes, at least, a CSR is needed for this.
> > 
> > I will file CSR for this PR after this discussion.
> 
> > > * Q3: What has to be done for statically linked agent?
> > 
> > JVMTI spec says "unless it is statically linked into the executable", so I think \
> > we can ignore about Agent_OnUnload_L() in this PR.
> 
> I don't think that makes sense. If you call it for dynamically linked then you need \
> to call it for statically linked also.

@dholmes-ora Thank you for explanation! I updated \
[CSR](https://bugs.openjdk.java.net/browse/JDK-8256918). Could you review it?

-------------

PR: https://git.openjdk.java.net/jdk/pull/19


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