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

[Chris Plummer]

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  }
>
>