JDK-8176828: jtools do not list VM process launched with the debugger option suspend=y

[David Holmes]

I've been lurking on this ...

On 29/11/2018 9:41 am, gary.adams at oracle.com wrote:
> On 11/28/18 4:12 PM, Chris Plummer wrote:
>> On 11/28/18 11:52 AM, Gary Adams wrote:
>>> https://bugs.openjdk.java.net/browse/JDK-8156537
>>>   - Added a fix for module naming
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8176533
>>>   - Fixed a regression from JDK-816537 that prevented "jcmd <pid> <cmd>"
>>>      from sending <cmd> to <pid>
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8176828
>>>   - Requests that "jcmd -l" should list the <pid>
>>>      for the VM that has not completed initialization.
>>>      This is not a regression, because jdk8 jcmd did
>>>      not display the uninitialized VM either.
>>>
>>> It appears you can send "jcmd <pid> <cmd>" to
>>> the process that has not completed vm initialization.
>> So what happens when you do this?
> The commands work, albeit the vm thread is blocked waiting for the
> debugger connection.

Define "work". If the VM is partially initialized there is very little 
that can be examined. If the VMThread is blocked on the debugger 
connection then you can't do anything that requires a VM operation 
(which includes safepoints - though at this stage if there are no 
JavaThreads we're safe anyway).

Thanks,
David

>>
>> Chris
>>>
>>> On 11/28/18, 2:29 PM, Chris Plummer wrote:
>>>> Sorry, meant to say "before JDK-8176533".
>>>>
>>>> Chris
>>>>
>>>> On 11/28/18 10:11 AM, Chris Plummer wrote:
>>>>> Hi Gary,
>>>>>
>>>>> This seems reasonable. I just want clarification on one thing 
>>>>> first. Before JDK-8176828, it listed the suspend=y process, but 
>>>>> could you do anything with it? I'm assuming no, and therefore it 
>>>>> makes sense not to list it at all.
>>>>>
>>>>> thanks,
>>>>>
>>>>> Chris
>>>>>
>>>>> On 11/28/18 8:33 AM, Gary Adams wrote:
>>>>>> I'd like to close JDK-8176828 as will not fix.
>>>>>>   https://bugs.openjdk.java.net/browse/JDK-8176828
>>>>>>
>>>>>> This bug was originally thought to be associated with
>>>>>> a regression fix in JDK-8176533, but I believe there
>>>>>> is simply a misunderstanding of how the "suspend=y"
>>>>>> behavior is supported for the jdwp agent library.
>>>>>>
>>>>>> The "suspend=y" setting is designed to maximize the number
>>>>>> of events that can been seen by an attaching debugger.
>>>>>> This calls for the process to be waiting for the debugger connection
>>>>>> before the VM has been completely initialized.
>>>>>>
>>>>>> In particular, the thread.cpp create_vm() function causes the
>>>>>> debugInit.c initialize() function to start the transport connection
>>>>>> and wait for an external debugger to attach. Once the dt_socket 
>>>>>> connection
>>>>>> is established the create_vm() function will complete. It is the
>>>>>> processing of the create_vm_timer.end() that results in the
>>>>>> management.cpp record_vm_startup_time() and the
>>>>>> PerfMemory::set_accessible(true) to be set.
>>>>>>
>>>>>> Without the accessible field being set an external program can not 
>>>>>> use
>>>>>> the PerfMemory. That is why "jcmd -l" passes over processes which
>>>>>> do not have an initialized VM running.
>>>>>>
>>>>>> =====
>>>>>> src/hotspot/share/runtime/:
>>>>>> src/jdk.jdwp.agent/share/native/libjdwp/:
>>>>>>
>>>>>>   thread.cpp:3587:jint Threads::create_vm(JavaVMInitArgs* args, 
>>>>>> bool* canTryAgain) {
>>>>>>   ...
>>>>>>   thread.cpp:3610:  create_vm_timer.start();
>>>>>>   ...
>>>>>>   thread.cpp:3907:  JvmtiExport::post_vm_initialized();
>>>>>>   ...
>>>>>>     debugInit.c:432:cbEarlyVMInit(jvmtiEnv *jvmti_env, JNIEnv 
>>>>>> *env, jthread thread)
>>>>>>     ...
>>>>>>     debugInit.c:103:static void initialize(JNIEnv *env, jthread 
>>>>>> thread, EventIndex triggering_ei);
>>>>>>     ...
>>>>>>     debugInit.c:732:    (void)bagEnumerateOver(transports, 
>>>>>> startTransport, &arg);
>>>>>>     ...
>>>>>>     debugInit.c:751:    transport_waitForConnection();
>>>>>>   ...
>>>>>>   thread.cpp:3955:  create_vm_timer.end();
>>>>>>
>>>>>> ====
>>>>>> src/hotspot/share/services/management.cpp:
>>>>>>
>>>>>>    203  void Management::record_vm_startup_time(jlong begin, jlong 
>>>>>> duration) {
>>>>>>    204    // if the performance counter is not initialized,
>>>>>>    205    // then vm initialization failed; simply return.
>>>>>>    206    if (_begin_vm_creation_time == NULL) return;
>>>>>>    207
>>>>>>    208    _begin_vm_creation_time->set_value(begin);
>>>>>>    209    _end_vm_creation_time->set_value(begin + duration);
>>>>>>    210    PerfMemory::set_accessible(true);
>>>>>>    211  }
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>>
>