On 12/04/2019 9:47 pm, Gary Adams wrote:
On 4/11/19, 8:16 PM, David Holmes wrote:
Hi Gary,
On 12/04/2019 4:24 am, Gary Adams wrote:
Two years ago a request was made to allow
jcmd help
to be interpretted as a request for help from the current jcmd process
rather than requiring a separate target process to be involved.
Some attempts were made to close the issue, because the
command was not documented to work that way.
It was also pointed out that the help from the running jcmd
might not match the cmds available from a subsequent
request to a different process possibly running a different version
of the vm.
As proof of concept exercise this webrev shows a minimal set of
changes that could support
jcmd self help
Before fleshing out additional changes in documentation and testing,
I'd like to know if this is still a worth while enhancement. Also,
Given we allow a pid of 0 to mean all Java processes I can see scope
for a special value that means "the current Java process", but using a
text word like "self" seems awkward at best. Plus within a shell you
can use: jcmd $$ help
$$ is the pid for the shell where the command is running,
not the jcmd pid.
Ooops. I thought there was a trick to pass the new process it's own pid
as an arg.
$ jcmd $$ help
17076:
com.sun.tools.attach.AttachNotSupportedException: Unable to open socket
file: target process not responding or HotSpot VM not loaded
at
sun.tools.attach.BsdVirtualMachine.<init>(BsdVirtualMachine.java:90)
at
sun.tools.attach.BsdAttachProvider.attachVirtualMachine(BsdAttachProvider.java:63)
at com.sun.tools.attach.VirtualMachine.attach(VirtualMachine.java:208)
at sun.tools.jcmd.JCmd.executeCommandForPid(JCmd.java:147)
at sun.tools.jcmd.JCmd.main(JCmd.java:131)
to act on the jcmd VM itself, so there doesn't need to be special
treatment in that sense. Perhaps some tweaks to the "jcmd -h" text.
If we did allow the self attach, we would need to update the help text.
I initially worked with -1 as another special value, but that looks a lot
like -l the list argument.
I'd like to know more about the history of the checks preventing self
attach.
This may give you a start:
https://bugs.openjdk.java.net/browse/JDK-8177154
I understand the dangers of agent loading and the arguments against
command line options and default settings that took place in jdk9
release.
I'm looking for something older that explains the rationale about
not allowing attach to the current process.
I'd suggest speaking to Alan or Mandy.
Cheers,
David
Cheers,
David
Webrev: http://cr.openjdk.java.net/~gadams/8177064/webrev/index.html
Issue: https://bugs.openjdk.java.net/browse/JDK-8177064
