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

[gary.adams at oracle.com]

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.
>
> 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  }
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>
>