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. :) I don't think we can expect new JNI users to be familiar with the exit hook, 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. 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. From: Thomas Stüfe <thomas.stu...@gmail.com> To: Adam Farley8 <adam.far...@uk.ibm.com> Cc: Java Core Libs <core-libs-dev@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 ). 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.far...@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
