RFR (M/L): 8131168: Refactor ProcessHandleImpl_*.c and add implememtation for AIX

Volker Simonis volker.simonis at gmail.com
Wed Aug 5 19:56:22 UTC 2015


so here's the webrev which implements the new Info.commandLine()
method (I chose 'commandLine() ' instead of 'cmdline()' or
'commandline()' because the other getters are camel case as well):


>From the JavaDoc of the new method:

* If {@code command()} and  {@code arguments()} return non-null
* optionals, this is simply a convenience method which concatenates
* the values of the two functions. Otherwise it will return a
* best-effort, platform dependent representation of the command line.

This didn't change anything on MacOS X where there is no additional
effort to get the command line.

On Solaris and AIX, Info.commandLine() will always return the contents
of psinfo.pr_psargs because there's no other method to get the exact
arguments (i.e. Info.arguments() always returns NULL. I could
therefore remove the extra handling of AIX/Solaris in the InfoTest
from my initial change.

On Linux, things are a little more complicated:

- the initial implementation for Linux used arg[0] as 'command' if
/proc/pid/exe wasn't readable. This was true for all the processes we
don't own (except if we are running as root). But this information may
be incomplete, because arg[0] may only contain the command without its
full path. One example is 'sendmail' for which Info.command() reported
"sendmail: accepting connections" but Info.arguments() was empty. This
is wrong, because 'sendmail' changes its argv[] array. I have
therefore disabled this behavior now that we have the 'commandLine()'

- /proc/pid/cmdline is limited to PAGE_SIZE (normally 4096) characters
on Linux. So strictly speaking, this isn't 'exact' information as well
(there are plenty of complains that especially for Java programs this
is not enough) and should go to 'commandLine()' instead to 'arguments'
if /proc/pid/cmdline is truncated. I do check for this now.

- the information in /proc/pid/cmdline can also be changed to
something other than the original arguments if a program changes
argv[] (which is not forbidden) but there's probably not much we can
do to detect this. I've added a corresponding @implNote comment to
JavaDoc of Info.arguments().

- the initial implementation did not check for incomplete reads of
/proc/pid/cmdline. This may be a problem on systems with PAGE_SIZE >
4096 (on Linux/ppc64 a page size of 65536 is not unusual). I'm now
always reading the complete contents of /proc/pid/cmdline.

- as far as I understand the current implementation, 'arguments()'
returns the arguments array WITHOUT 'arg[0]' (which is the program
name) but may
be we should specify that more clearly in the JavaDoc of 'arguments()'.

That's it. Hope you like it :)


On Fri, Jul 31, 2015 at 11:02 PM, Stuart Marks <stuart.marks at oracle.com> wrote:
> Hi Roger, Volker,
> Glad to see you guys are receptive to this and that it can move forward. Let
> me know if you'd like me to help out, for example with reviews or something.
> s'marks
> On 7/31/15 9:55 AM, Roger Riggs wrote:
>> Hi Volker,
>> I agree that adding an Info.commandline() method would be a good way
>> to make the command line available and be able to describe that it is
>> OS dependent and may be truncated.
>> And having it assemble the command and arguments when they are available
>> makes
>> sense.
>> As an API addition it will need a clear spec and I can run it through CCC
>> so it
>> gets
>> another review and compatibility tests.
>> Thanks, Roger
>> On 7/31/2015 5:03 AM, Volker Simonis wrote:
>>> On Fri, Jul 31, 2015 at 2:51 AM, Stuart Marks <stuart.marks at oracle.com>
>>> wrote:
>>>> On 7/29/15 11:36 AM, Volker Simonis wrote:
>>>>>> !! ProcessHandleImpl_unix: 709-738:  I still disagree with returning
>>>>>> truncated or incomplete
>>>>>> values for the executable or arguments.
>>>>>> Can anyone be a tie-breaker  (with a good rational and suggestion for
>>>>>> how
>>>>>> an
>>>>>> application can use the data).
>>>>> As I wrote, I agree to hear other opinions here.
>>>>> All I want to say that this truncated data is actually what 'ps' is
>>>>> reporting on Solaris since decades and people seem to be happy with
>>>>> it. As use case I can imagine logging or monitoring (something like
>>>>> 'top' in Java) where this data will be just good enough.
>>>>> We could specially mark possibly incomplete data by extending the Info
>>>>> object with functions like commandIsExact() or argumentsIsPrecise().
>>>>> But notice that we can not statically preset these values per
>>>>> platform. For example on Solaris, the 'command()' would return a
>>>>> precise value for processes with the same uid like the VM but only
>>>>> inaccurate values for all other processes. The "arguments()" would be
>>>>> always inaccurate on Solaris/AIX.
>>>> It seems like there are cases where either exact or only approximate
>>>> information is available. And as you observed, you might get one or the
>>>> other on the same platform, depending on the UID. It also might depend
>>>> on
>>>> process state; I believe that some information becomes inaccessible when
>>>> the
>>>> process enters the zombie state.
>>>> I don't think we should simply ignore one case or the other, but I also
>>>> don't think we should try to cram the different information into the
>>>> same
>>>> API.
>>>> The current ProcessHandle.Info api has
>>>>      Optional<String> command()
>>>>      Optional<String[]> arguments()
>>>> It sounds to me like Roger wants these to contain only exact
>>>> information.
>>>> That seems reasonable, and this probably needs to be specified more
>>>> clearly
>>>> to contrast with what's below.
>>>> On Solaris, the psinfo_t struct has char pr_psargs[PRARGSZ] which is a
>>>> single string which appears to be the concatenation of the arguments
>>>> (maybe
>>>> including the command name). It's also truncated to fit PRARGSZ. It
>>>> doesn't
>>>> make sense to me to try to return this as a String[], as the zeroth
>>>> element
>>>> of that array, and certainly not parsed out into "words". So maybe
>>>> instead
>>>> we should have a different API that returns an imprecise command line as
>>>> a
>>>> single string:
>>>>      Optional<String> cmdline()
>>>> (Naming bikeshed TBS). The semantics would be that this is the process'
>>>> command and arguments concatenated into a single string (thus
>>>> potentially
>>>> losing argument boundaries) and also possibly truncated based on
>>>> platform
>>>> (COUGHsolarisCOUGH) limitations. It's certainly useful for printing out
>>>> in a
>>>> ps, top, or Activity Monitor style application, for informational
>>>> purposes.
>>>> If this were implemented, then on Solaris, command() and arguments()
>>>> would
>>>> always return empty optionals.
>>>> I'm not sure what this should be if the exact information is available.
>>>> It
>>>> would be inconvenient if something that just wanted to print out an
>>>> approximate command line had to check several different APIs to get the
>>>> information. Maybe cmdline() could assemble the information from exact
>>>> data
>>>> if it's is available, by concatenating the Strings from command() and
>>>> arguments(), as a convenience to the caller. But I could go either way
>>>> on
>>>> this.
>>>> Not sure this counts as a tie-breaker, but it might be a reasonable way
>>>> forward.
>>>> s'marks
>>> Hi Stuart,
>>> thanks a lot for your comments - I like your proposal. For me this
>>> sounds like a good compromise.
>>> @Roger: should I go and add a new field commandLine and the
>>> corresponding getter to the Info class? As Stuart proposed, the getter
>>> could check if 'command' and 'arguments' are available and assemble
>>> the command line from them. Otherwise it could use the content of the
>>> commandLine field if that is available.
>>> Regards,
>>> Volker

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