Hi Gary,
Somewhere in this I got the mistaken impression that it is the VMThread
that blocks waiting for the debugger to attach, but it is actually the
main thread executing create_vm. That simplifies things and addresses
the concern I had about jcmds that needed VM ops.
So IIUC the only reason we can't attach is because PerfMemory is not
"accessible" so the patch below addresses that by making it accessible
before the main thread would block. I've looked at the initialization
flow and moving the set_accessible call seems reasonable to me.
Thanks,
David
On 30/11/2018 10:38 pm, Gary Adams wrote:
Here's a smaller change. I'll run through a bunch of serviceability
tests to make sure
this early accessible setting does not have any unexpected side effects..
diff --git a/src/hotspot/share/runtime/thread.cpp
b/src/hotspot/share/runtime/thread.cpp
--- a/src/hotspot/share/runtime/thread.cpp
+++ b/src/hotspot/share/runtime/thread.cpp
@@ -3902,6 +3902,9 @@
// may be attached late and JVMTI must track phases of VM execution
JvmtiExport::enter_live_phase();
+ // Make perfmemory accessible
+ PerfMemory::set_accessible(true);
+
// Notify JVMTI agents that VM initialization is complete - nop if
no agents.
JvmtiExport::post_vm_initialized();
On 11/30/18, 5:03 AM, [email protected] wrote:
It turns out that almost all the diagnostic commands provide
meaningful output even though the vm thread is not totally
initialized.
We could declare the perfmemory initialized a little earlier ...
diff --git a/src/hotspot/share/runtime/thread.cpp
b/src/hotspot/share/runtime/thread.cpp
--- a/src/hotspot/share/runtime/thread.cpp
+++ b/src/hotspot/share/runtime/thread.cpp
@@ -3902,6 +3902,9 @@
// may be attached late and JVMTI must track phases of VM execution
JvmtiExport::enter_live_phase();
+ // Make perfmemory accessible
+ create_vm_timer.end();
+
// Notify JVMTI agents that VM initialization is complete - nop if
no agents.
JvmtiExport::post_vm_initialized();
@@ -3951,7 +3954,6 @@
}
}
- create_vm_timer.end();
#ifdef ASSERT
_vm_complete = true;
#endif
This would be the "jcmd -l" output when the post_vm_initialized()
would block on the "suspend=y" processing
23732 jdk.jcmd/sun.tools.jcmd.JCmd -l
22526 Unknown
... when the debugger attaches "jdb -attach 5900"
23771 jdk.jdi/com.sun.tools.example.debug.tty.TTY -attach 5900
23884 jdk.jcmd/sun.tools.jcmd.JCmd -l
22526 Unknown
... when the debugger starts with the "run" command
23922 jdk.jcmd/sun.tools.jcmd.JCmd -l
23771 jdk.jdi/com.sun.tools.example.debug.tty.TTY -attach 5900
22526 my
We could also pull out the perfmemory set accessible step
and set it explicitly.
...
On 11/28/18 11:10 PM, David Holmes wrote:
I've been lurking on this ...
On 29/11/2018 9:41 am, [email protected] 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 }
