RFR(XS) 8212612 - Add documentation about Arguments::_exit_hook

[dean.long at oracle.com]

On 10/17/18 9:33 AM, Ioi Lam wrote:
> http://cr.openjdk.java.net/~iklam/jdk12/8212612-exit-hook-docs.v01/
> https://bugs.openjdk.java.net/browse/JDK-8212612
>
> The following fields are assigned to according to 
> JavaVMOption.optionString.
>
>   abort_hook_t Arguments::_abort_hook = NULL;
>   exit_hook_t Arguments::_exit_hook = NULL;
>   vfprintf_hook_t Arguments::_vfprintf_hook = NULL;
>
> However, there's no code in the JDK repo that uses these options.
> Instead, they are intended for programs that embed the JVM using
> JNI_CreateJavaVM.
>
> We should add comments in arguments.cpp for clarification. Otherwise
> this would look like dead code and someone might be tempted to
> remove it.
>
> Thanks
> - Ioi

But it's not dead code.  All three are used.  For example, see 
jio_vfprintf().

dl