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

[Chris Plummer]

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?

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  }
>>>>
>>>>
>>>
>>>
>>
>>
>