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

[dean.long at oracle.com]

On 10/17/18 3:44 PM, Ioi Lam wrote:
>
>
>
> On 10/17/2018 02:59 PM, dean.long at oracle.com wrote:
>> On 10/17/18 2:35 PM, Ioi Lam wrote:
>>>
>>>
>>> On 10/17/2018 02:27 PM, dean.long at oracle.com wrote:
>>>> 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
>>>
>>> Hi Dean, thanks for looking into this.
>>>
>>> I was afraid someone would infer that since nowhere in the JDK code 
>>> would do anything to assign _vfprintf_hook to a non-NULL value, the 
>>> block
>>>
>>>   if (Arguments::vfprintf_hook() != NULL) {
>>>     jio_fprintf(defaultStream::output_stream(), "%.*s", (int)len, s);
>>>   }
>>>
>>> would be effectively dead code.
>>>
>>
>> OK, then this comment was confusing:
>>
>> These are not used by the JDK itself
>>
>> I think it's more accurate to say that JDK launchers don't set these, 
>> but the JVM does use and honor them if set.
>>
>
> How about this:
>
> // These are not set by the JDK's built-in launchers, but they can be 
> set by programs that
> // embed the JVM using JNI_CreateJavaVM. See comments around 
> JavaVMOption in jni.h.
> abort_hook_t     Arguments::_abort_hook         = NULL;
> exit_hook_t      Arguments::_exit_hook          = NULL;
> vfprintf_hook_t  Arguments::_vfprintf_hook      = NULL;
>
>

That's good!

dl

> Thanks
> - Ioi
>