[BUG PROPOSAL]: C++ code that calls JNI_CreateJavaVM can be exited by java

[Thomas Stüfe]

Hi Adam,

Copying hotspot-dev.

Please find my answers inline.

On Wed, Aug 23, 2017 at 8:51 PM, Adam Farley8 <adam.farley at uk.ibm.com>
wrote:

> Hi Thomas,
>
> First, thank you for your time. :)
>
> The exit hook you recommend sounds like a fine workaround, though I
> suggest a return code would make a better long term solution.
>
> Especially if the exit hook might be broken. :)
>
>
Then it would be better to fix it instead of introducing a new option.


> I don't think we can expect new JNI users to be familiar with the exit
> hook,


Why? It is part of the API.


> and having Java designed to use the nuclear option (exit(0)) for a mere
> help option seems like overkill.
>
> From what you're saying, I think you're agreeing that it's better to pass
> a negative return code than call exit(#) and catch it, so that the VM can
> shut down "cleanly" instead of being suddenly terminated by a random chunk
> of internal c code.
>

I do not understand that sentence :)

Neither option (1 - calling exit(2) with the option for the caller to
intercept it or 2 - returning a to-be-newly-defined return code from
JNI_CreateJavaVM) guarantee a clean VM shutdown. More has to be done for
that. All it does is to give the caller the option to run its own cleanup,
an option which arguably already exists in the form of the exit hook.


>
> Does this sound correct?
>
> Best Regards
>
> Adam Farley
>
> P.S I should note that, if we agree to go ahead with the negative return
> code, we'll need to modify java.c to ignore it. IMO: Help options should
> only return negative return codes to JNI callers, not java executable users.
>
>
Kind Regards, Thomas


>
>
>
> From:        Thomas Stüfe <thomas.stuefe at gmail.com>
> To:        Adam Farley8 <adam.farley at uk.ibm.com>
> Cc:        Java Core Libs <core-libs-dev at openjdk.java.net>
> Date:        23/08/2017 18:45
> Subject:        Re: [BUG PROPOSAL]: C++ code that calls JNI_CreateJavaVM
> can be exited by java
> ------------------------------
>
>
>
> Hi Adam,
>
> would the JNI exit hook not solve your problem (JavaVMOption "exit")? One
> could use it to intercept any exit(2) calls.
>
> However, I am not sure it always fires, and if it does not, whether this
> should be considered a bug. The official JNI documentation is pretty sparse
> (
> *http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/invocation.html*
> <http://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/invocation.html>
> ).
>
> Another thing, even if one catches ::exit(), if the VM creation failed the
> process can be in an undefined state, because I am not sure we clean up
> orderly for every error exit. So, e.g., signal handlers may still be
> installed etc.
>
> Kind Regards, Thomas
>
>
>
>
> On Wed, Aug 23, 2017 at 5:54 PM, Adam Farley8 <*adam.farley at uk.ibm.com*
> <adam.farley at uk.ibm.com>> wrote:
> Hi All,
>
> Problem: Several of Java's "c" files call exit(0) if you pass certain
> command-line options to JNI_CreateJavaVM, which can terminate the C++ code
> JNI users use to initialise the JVM.
>
> Example: If you write some C++ code that calls JNI_CreateJavaVM, and uses
> the option "-agentlib:jdwp=help", Java's c files will print the needed
> help output and call exit(0).
>
> Result: Your C++ code is terminated on this line, and a return code of 0
> is produced.
>
> Issues:
>
> Issue 1: The exit(0) prevents your code from doing anything useful after
> the JNI_CreateJavaVM call.
> Issue 2: The exit(0) indicates to anything monitoring your C++ code that
> your code exited normally, even though it was terminated mid-way-through.
> Issue 3: This return code is useless to us, as a 0 can indicate the VM
> started correctly, or it can indicate the VM was terminated due to one or
> more of these command-line options.
> Issue 4: Of the other JNI return values (JNI_OK, JNI_ERR, etc) none of
> them appear to cover this scenario.
>
>
> Proposed solutions:
>
> PS1: We should amend the JNI specification to include a "JNI_SILENT_EXIT"
> return code, so the C++ code knows a VM was not created, but that it isn't
> an error.
> PS2: We should identify a list of the command-line options that produce
> this behaviour via the JNI. (not all of the "help" options are recognised
> by the JNI interface. E.g. -version and -help produce a JNI_ERR and an
> "Option not recognised" message)
> PS3: We should replace these annoying exit(0) calls with code that returns
> "JNI_SILENT_EXIT", so the C++ code has a chance to finish.
>
>
> Best Regards
>
> Adam Farley
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>
>
>
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>