On Fri, 2 Oct 2020 07:27:43 GMT, Yasumasa Suenaga <ysuen...@openjdk.org> wrote:
>> I was initially wrong by supporting this, and now I share David's concerns >> about unclear semantics of this. The >> questions are: >> - Q1: Is it necessary to call the Agent_OnUnload()? >> - Q2: Would it be a JVMTI spec violation to call the Agent_OnAttach() >> multiple times? (It seems to be the case to me.) >> - Q3: What has to be done for statically linked agent? >> - Q4: Should the agent be correctly loadable in the first place? What were >> the reasons its loading to fail? >> >> Yes, at least, a CSR is needed for this. > >> * 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. If we can change the spec that agent library would not be unloaded when `Agent_OnAttach()` failed, we can change like [webrev.00](https://cr.openjdk.java.net/~ysuenaga/JDK-8252657/webrev.00/). It is simple, and similar behavior with `Agent_OnLoad()`. It might be prefer for JVMTI agent developers. ------------- PR: https://git.openjdk.java.net/jdk/pull/19
