RFR: JDK-8147388: Add diagnostic commands to attach JVMTI agent.

[Yasumasa Suenaga]

Hi Dmitry,

> Otherwise looks good for me (I'll sponsor the push).

Thanks!

> 1. It's better to check _libpath.value() and write a message, that the
> parameter is required.

I set true to 4th argument (mandatory) of DCmdArgument c'tor.
If we execute jcmd without libpath, we get message as below:
-----------
$ jcmd 939 JVMTI.javaagent_load
939:
java.lang.IllegalArgumentException: The argument 'library path' is mandatory.
-----------

> 2.  It might be better to avoid malloc here by pre-calcualting length of
> required option length and than declare
> 
> char *new_options[new_options_len];

Sorry, I could not understand details.

We have to be different way for option string of libinstrument.
If option value is not NULL, we have to build string like <libpath>=<option>
as argument of libinstrument. Otherwise, we can pass libpath only to libinstrument.

I use malloc() and strdup() to build option string to pass to libinstrument.so .


Thanks,

Yasumasa


On 2016/01/15 0:06, Dmitry Samersoff wrote:
> Yasumasa,
> 
> diagnosticCommand.cpp:294
> 
> 1. It's better to check _libpath.value() and write a message, that the
> parameter is required.
> 
> 2.  It might be better to avoid malloc here by pre-calcualting length of
> required option length and than declare
> 
> char *new_options[new_options_len];
> 
> Otherwise looks good for me (I'll sponsor the push).
> 
> -Dmitry
> 
> 
> On 2016-01-14 17:00, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> We can use Attach API to attach JVMTI agent to live process.
>> However, we have to write Java code for it.
>>
>> If we can attach JVMTI agents through jcmd, it is very useful.
>> So I want to add two new diagnostic commands:
>>
>>   * JVMTI.agent_load: Load JVMTI native agent.
>>   * JVMTI.javaagent_load: Load JVMTI java agent.
>>
>> I maintain two JVMTI agents - HeapStats [1] and JLivePatcher [2].
>> [1] is native agent, [2] is java agent.
>> They provide a program for attaching to live process.
>>
>> I guess that various JVMTI agents provide own attach mechanism like them.
>> I think that we should provide general way to attach.
>>
>> I've uploaded webrev. Could you review it?
>>    http://cr.openjdk.java.net/~ysuenaga/JDK-8147388/webrev.00/
>>
>> I'm jdk9 committer, however I cannot access JPRT.
>> So I need a sponsor.
>>
>>
>> Thanks,
>>
>> Yasumasa
>>
>>
>> [1] http://icedtea.classpath.org/wiki/HeapStats
>> [2] https://github.com/YaSuenag/jlivepatcher  (in Japanese)
>>
> 
>