8178380: Module system implementation refresh (5/2017 update)

[Alan Bateman]

On 02/05/2017 20:21, stanislav lukyanov wrote:

> Hi Alan,
>
> In the Launcher-Agent-Class, would it make sense to use 'premain' 
> instead of 'agentmain'
> to align it with Premain-Class rather than with Agent-Class?
> (maybe even rename Launcher-Agent-Class to Launcher-Premain-Class?)
>
> AFAIU Launcher-Agent-Class is meant to replace a particular use case 
> of self-attach in applications - hence the 'agentmain'.
> But on the other hand, it is essentially a "shortcut" for '-jar 
> app.jar -javaagent:app.jar', so 'premain' might as well be expected to 
> be used (especially by a new user).
>
> Also Launcher-Agent-Class is invoked before the application, like 
> Premain-Class and unlike Agent-Class,
> and some agents out there might use the entry method (premain or 
> agentmain declared by the same class) to determine how they were invoked.
> It will not be possible if 'agentmain' can be invoked both before and 
> after 'main'
> (using different classes for Premain-Class, Agent-Class and 
> Launcher-Agent-Class will still work though).
Executable JARs is a launcher concept, specified in the JAR file spec, 
and not something that the VM knows anything about. You won't see 
anything about executable JARs in the JNI invocation interface for 
example. This means that the agent declared via Launcher-Agent-Class is 
started in a running VM and is more like Agent-Class/agentmain than 
Premain-Class/premain. In particular, it may not be possible to get all 
the capabilities that an agent specified via `-javaagent` can get. So I 
think the proposed names are okay.

As regards using an executable JAR with `-javaagent`, or a tool loading 
the executable JAR as an agent library into a running VM, then I think 
there is enough flexibility with using different class names.

-Alan.