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

[Thomas Stüfe]

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
).

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>
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
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