MethodHandle initialization process - problem with JVM TI early VM start event

[Alan Bateman]

On 04/01/2017 10:39, David Holmes wrote:

>
> That is my thought too, that the spec needs to give less of the 
> impression that it's okay to access java.base classes at this early VM 
> start event, and basically say that any form of class-loading is not 
> guaranteed to succeed and will quite likely crash the JVM.
The JVM TI spec has always allowed agents to call any JNI function in 
the start phase. I don't think there was any intention to have agents 
load and execute arbitrary java code but this wasn't fully spelled out. 
For JDK 9 then we attempt to preserve this compatibility for existing 
agents by deferring the start phase until after the module system is 
initialized (initPhase2). This has the side effect that they miss out on 
some interesting events during startup. They can of course replay at 
least some of them with GenerateEvents but it's not enough for some 
agents. So this is the reason for the can_generate_early_vmstart 
capability and it's intended for agents that take an oath of carefulness.

So for the spec update then I think the restrictions can be mostly 
limited to when the can_generate_early_vmstart capability is enabled. 
Ideally we should avoid introducing yet another event that signals the 
point in the start phase when it's safe to do things, agents can use the 
VMInit for that.

-Alan