2017/4/6 10:48:12 -0700, alasdair.notting...@gmail.com: > On Apr 5, 2017, at 12:15 PM, mark.reinh...@oracle.com wrote: >> >> Thanks to everyone for the quick feedback on this topic, and especially >> to Andrew for the constructive dialogue. >> >> Here's a revised proposal: >> >> - Define a new VM option, `-XX:+EnableDynamicAgentLoading`, that's >> on by default in JDK 9 but off by default in JDK 10. >> >> This will allow launch scripts that use this option on JDK 10 to >> work on JDK 9 without change, and will allow early testing of the >> JDK 10 behavior on JDK 9. > > I think giving more time to react to the change is good, but I think this just > provides more notice that dynamic attach will go away, it doesn’t ultimately > provide a solution for the problems that are currently solved using dynamic > attach of agents.
As Andrew Dinn writes nearby there really isn't a solution here, per se, there's just a tradeoff between flexibility and performance. >> - Revise the `com.sun.tools.attach` API to forbid attachment to the >> current process or to an ancestor of the current process, and >> define a read-only system property that allows such attachment to >> be enabled via the command line. >> >> This will discourage the inadvertent use of libraries that, for >> better or for worse, intentionally violate strong encapsulation. > > I think just preventing self-attach would be enough. I don’t think you need > to worry about the hierarchy. If you are going to the lengths of launching new > JVM’s to attach the agent I’m pretty sure that you have found out that you > cannot self attach, and are therefore already in the camp of knowing you are > doing something bad. Yes, I suspect you're right. We'll just forbid self-attachment for now. >> - Enhance the `-jar` launcher option so that if the JAR file being >> launched contains a `Premain-Class` attribute then it's launched >> as both an application and as an agent for that application. >> >> This will allow `java -jar foo.jar` to be used in place of the >> more verbose `java -javaagent:foo.jar -jar foo.jar` [1]. >> > > I like this idea, it solves my problem in a much simpler way than having to > self attach. I don’t mind what the header is called, so if Self-Premain-Class > is > used I can cope with that. Please see my nearby reply to Michael Rasumussen -- the new attribute will be named `Launcher-Agent-Class`. > I’m assuming this will continue to work in Java SE > 10 > and only dynamic attach will be disabled in Java SE 10. `Launcher-Agent-Class` is a form of dynamic agent loading but it's well-scoped and not so easy to use inadvertently, so I suspect it will do no harm to leave it enabled even when dynamic loading via attachment is disabled by default. - Mark
